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14544425
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Salutaridinol 7-O-acetyltransferase
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In enzymology, a salutaridinol 7-O-acetyltransferase (EC 2.3.1.150) is an enzyme that catalyzes the chemical reaction
acetyl-CoA + salutaridinol formula_0 CoA + 7-O-acetylsalutaridinol
Thus, the two substrates of this enzyme are acetyl-CoA and salutaridinol, whereas its two products are CoA and 7-O-acetylsalutaridinol.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acetyl-CoA:salutaridinol 7-O-acetyltransferase. This enzyme participates in alkaloid biosynthesis i.
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14544446
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Serine C-palmitoyltransferase
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In enzymology, a serine "C"-palmitoyltransferase (EC 2.3.1.50) is an enzyme that catalyzes the chemical reaction:
palmitoyl-CoA + L-serine formula_0 CoA + 3-dehydro-D-sphinganine + CO2
Thus, the two substrates of this enzyme are palmitoyl-CoA and L-serine, whereas its 3 products are CoA, 3-dehydro-D-sphinganine, and CO2. This reaction is a key step in the biosynthesis of sphingosine which is a precursor of many other sphingolipids.
This enzyme participates in sphingolipid metabolism. It employs one cofactor, pyridoxal phosphate.
Nomenclature.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is palmitoyl-CoA:L-serine "C"-palmitoyltransferase (decarboxylating). Other names in common use include:
Structure.
Serine "C"-palmitoyltransferase is a member of the AOS (a-oxoamine synthase) family of PLP-dependent enzymes, which catalyse the condensation of amino acids and acyl-CoA thioester substrates. The human enzyme is a heterodimer consisting of two monomeric subunits known as long chain base 1 and 2 (LCB1/2) encoded by separate genes. The active site of LCB2 contains lysine and other key catalytic residues that are not present in LCB1, which does not participate in catalysis but is nevertheless required for the synthesis and stability of the enzyme.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2JG2 and 2JGT.
Mechanism.
The PLP (pyridoxal 5′-phosphate)-dependent serine "C"-palmitoyltransferase carries out the first enzymatic step of "de novo" sphingolipid biosynthesis. The enzyme catalyses a Claisen-like condensation between L-serine and an acyl-CoA thioester (CoASH) substrate (typically C16-palmitoyl) or an acyl-ACP (acyl-carrier protein) thioester substrate, to form 3-ketodihydrosphingosine. Initially PLP cofactor is bound to the active-site lysine via a Schiff base to form the holo-form or internal aldimine of the enzyme. The amine group of L-serine then attacks and displaces the lysine bound to PLP, forming the external aldimine intermediate. Subsequently, deprotonation occurs at the Cα of serine, forming the quinonoid intermediate that attacks the incoming thioester substrate. Following decarboxylation and lysine attack, the product 3-keto-dihydrosphingosine is released and catalytically active PLP is reformed. This condensation reaction forms the sphingoid base or long-chain base found in all subsequent intermediate sphingolipids and complex sphingolipids in the organism.
Isoforms.
A variety of different serine "C"-palmitoyltransferase isoforms exist across different species. Unlike in eukaryotes, where the enzyme is heterodimeric and membrane bound, bacterial enzymes are homodimers and cytoplasmic. Studies of the isoform of the enzyme found in the Gram-negative bacterium "Sphingomonas paucimobilis" were the first to elucidate the structure of the enzyme, revealing that PLP cofactor is held in place by several active site residues including Lys265 and His159. Specifically, the "S. paucimobilis" isoform features an active-site arginine residue (Arg378) that plays a key role in stabilizing the carboxy moiety of the PLP-L-serine external aldimine intermediate. Similar arginine residues in enzyme homologues (Arg370, Arg390) play analogous roles.
Other homologues, such as in "Sphingobacterium multivorum", feature the carboxy moiety bound to serine and methionine residues via water in place of arginine. Certain enzyme homologues, such as in "S. multivorum" as well as "Bdellovibrio stolpii", are found to be associated with the inner cell membrane, thus resembling the eukaryotic enzymes. The "B. stolpii" homologue also features substrate inhibition by palmitoyl-CoA, a feature shared by the yeast and mammalian homologues.
Clinical significance.
HSAN1 (hereditary sensory and autonomic neuropathy type 1) is a genetic disorder caused by mutations in either one of "SPTLC1" or "SPTLC2", genes encoding the two heterodimeric subunits of the eukaryotic serine C-palmitoyltransferase enzyme. These mutations have been shown to alter active site specificity, specifically by enhancing the ability of the enzyme to condense L-alanine with the palmitoyl-CoA substrate. This is consistent with elevated levels of deoxysphingoid bases formed by the condensation of alanine with palmitoyl-CoA observed in HSAN1 patients.
Species distribution.
Serine "C"-palmitoyltransferase is expressed in a large number of species from bacteria to humans. The bacterial enzyme is a water-soluble homodimer whereas in eukaryotes the enzyme is a heterodimer which is anchored to the endoplasmic reticulum. Humans and other mammals express three paralogous subunits SPTLC1, SPTLC2, and SPTLC3. It was originally proposed that the functional human enzyme is a heterodimer between a SPTLC1 subunit and a second subunit which is either SPTLC2 or SPTLC3. However more recent data suggest that the enzyme may exist as a larger complex, possibly an octamer, comprising all three subunits.
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14544460
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Serine O-acetyltransferase
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In enzymology, a serine O-acetyltransferase (EC 2.3.1.30) is an enzyme that catalyzes the chemical reaction
acetyl-CoA + -serine formula_0 CoA + "O"-acetyl--serine
Thus, the two substrates of this enzyme are acetyl-CoA and -serine, whereas its two products are CoA and "O"-acetyl--serine.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acetyl-CoA:L-serine O-acetyltransferase. Other names in common use include SATase, L-serine acetyltransferase, serine acetyltransferase, and serine transacetylase. This enzyme participates in cysteine metabolism and sulfur metabolism.
Structural studies.
As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes 1S80, 1SSM, 1SSQ, 1SST, 1T3D, 1Y7L, and 2ISQ.
N terminal protein domain.
In molecular biology, the protein domain SATase is short for Serine acetyltransferase and refers to an enzyme that catalyses the conversion of -serine to -cysteine in E. coli. More specifically, its role is to catalyse the activation of -serine by acetyl-CoA.This entry refers to the N-terminus of the protein which has a sequence that is conserved in plants and bacteria.
Importance of function.
The N-terminal domain of the protein Serine acetyltransferase helps catalyse acetyl transfer. This particular enzyme catalyses serine into cysteine which is eventually converted to the essential amino acid methionine. Of particular interest to scientists, is the ability to harness the natural ability of the enzyme, Serine acetyltransferase, to create nutritionally essential amino acids and to exploit this ability through transgenic plants. These transgenic plants would contain more essential sulphur amino acids meaning a healthier diet for humans and animals.
Structure.
The amino-terminal alpha-helical domain particularly the amino acid residues His158 (histidine in position 158) and Asp143 (aspartic acid in position 143) form a catalytic triad with the substrate for acetyl transfer. There are eight alpha helices that form the N-terminal domain.
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14544479
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Shikimate O-hydroxycinnamoyltransferase
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In enzymology, a shikimate O-hydroxycinnamoyltransferase (EC 2.3.1.133) is an enzyme that catalyzes the chemical reaction
4-coumaroyl-CoA + shikimate formula_0 CoA + 4-coumaroylshikimate
Thus, the two substrates of this enzyme are 4-coumaroyl-CoA and shikimate, whereas its two products are CoA and 4-coumaroylshikimate.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is 4-coumaroyl-CoA:shikimate O-(hydroxycinnamoyl)transferase. This enzyme is also called shikimate hydroxycinnamoyltransferase. This enzyme participates in phenylpropanoid biosynthesis.
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14544498
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Sinapoylglucose—choline O-sinapoyltransferase
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In enzymology, a sinapoylglucose---choline O-sinapoyltransferase (EC 2.3.1.91) is an enzyme that catalyzes the chemical reaction
1-O-sinapoyl-beta-D-glucose + choline formula_0 D-glucose + sinapoylcholine
Thus, the two substrates of this enzyme are 1-O-sinapoyl-beta-D-glucose and choline, whereas its two products are D-glucose and sinapoylcholine (sinapine).
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is 1-O-(4-hydroxy-3,5-dimethoxycinnamoyl)-beta-D-glucose:choline 1-O-(4-hydroxy-3,5-dimethoxycinnamoyl)transferase. This enzyme is also called sinapine synthase. This enzyme participates in phenylpropanoid biosynthesis.
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14544521
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Sinapoylglucose—malate O-sinapoyltransferase
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In enzymology, a sinapoylglucose---malate O-sinapoyltransferase (EC 2.3.1.92) is an enzyme that catalyzes the chemical reaction
1-O-sinapoyl-beta-D-glucose + (S)-malate formula_0 D-glucose + sinapoyl-(S)-malate
Thus, the two substrates of this enzyme are 1-O-sinapoyl-beta-D-glucose and (S)-malate, whereas its two products are D-glucose and sinapoyl-(S)-malate.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is 1-O-sinapoyl-beta-D-glucose:(S)-malate O-sinapoyltransferase. Other names in common use include 1-sinapoylglucose-L-malate sinapoyltransferase, and sinapoylglucose:malate sinapoyltransferase. This enzyme participates in phenylpropanoid biosynthesis.
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14544539
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Sinapoylglucose—sinapoylglucose O-sinapoyltransferase
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In enzymology, a sinapoylglucose---sinapoylglucose O-sinapoyltransferase (EC 2.3.1.103) is an enzyme that catalyzes the chemical reaction
2 1-O-sinapoyl beta-D-glucoside formula_0 D-glucose + 1,2-bis-O-sinapoyl beta-D-glucoside
Hence, this enzyme has one substrate, 1-O-sinapoyl beta-D-glucoside, and two products, D-glucose and 1,2-bis-O-sinapoyl beta-D-glucoside.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is 1-O-(4-hydroxy-3,5-dimethoxycinnamoyl)-beta-D-glucoside:1-O-(4-hydro xy-3,5-dimethoxycinnamoyl-beta-D-glucoside 1-O-sinapoyltransferase. Other names in common use include hydroxycinnamoylglucose-hydroxycinnamoylglucose, hydroxycinnamoyltransferase, 1-(hydroxycinnamoyl)-glucose:1-(hydroxycinnamoyl)-glucose, and hydroxycinnamoyltransferase.
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14544554
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Sphingosine N-acyltransferase
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In enzymology, sphingosine N-acyltransferases (ceramide synthases (CerS), EC 2.3.1.24) are enzymes that catalyze the chemical reaction of synthesis of ceramide:
acyl-CoA + sphingosine formula_0 CoA + N-acylsphingosine
Thus, the two substrates of this enzyme are acyl-CoA and sphingosine, whereas its two products are CoA and N-acylsphingosine.
Ceramide synthases are integral membrane proteins of the endoplasmic reticulum.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acyl-CoA:sphingosine N-acyltransferase. Other names in common use include ceramide synthetase, and sphingosine acyltransferase. This enzyme participates in sphingolipid metabolism.
History.
CerS were originally called Lass ("L"ongevity "ass"urance) genes because of their homology to the yeast protein, longevity assurance gene-1 (LAG1p), and they were later renamed due to the discovery of their biological function.
LAG1 in yeast was discovered in 1994 and named for the discovery that its deletion prolonged life span of" Saccharomyces cerevisiae" by almost 50%. In the following years, it and its homologs were shown to be required for the syntheses of ceramides found in yeast. Three years previously, the mammalian gene upstream of growth and differentiation factor-1 (UOG-1) was discovered, but it wasn't until 2005 that it was defined as the first mammalian CerS, when Sujoy Lahiri and Tony Futerman from the Weizmann Institute of Science found that LASS5 is a bona fide mammalian ceramide synthase that specifically synthesizes palmitoyl (C16) ceramide.
Function.
CerS are involved in the "de novo" synthesis pathway of ceramides. Their role is acylation coupling of sphinganine to a long-chain fatty acid to form a dihydroceramide, before the double bond is introduced to position 4 of the sphingoid base.
Genetic Characteristics.
CerS contain a unique C-terminal domain called the TLC domain and both mammalian and yeast CerS have 5–8 transmembrane domains. All mammalian CerS, aside from CerS1, contain a Hox-like domain shared by transcription factors important in development, although the first 15 amino acids of this domain are missing in CerS, indicating that this domain likely does not function as a genuine transcription factor.
Mammalian CerS.
Six mammalian CerS have been described, with each utilizing fatty acyl CoAs of relatively defined chain lengths for N‑acylation of the sphingoid long chain base. Mammals contain six distinct CerS, whereas most other enzymes in the sphingolipid biosynthetic pathway only occur in one or two isoforms.
Ceramide synthases include:
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14544576
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Sterol O-acyltransferase
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Class of enzymes
Sterol O-acyltransferase (also called Acyl-CoA cholesterol acyltransferase, Acyl-CoA cholesterin acyltransferase or simply ACAT) is an intracellular protein located in the endoplasmic reticulum that forms cholesteryl esters from cholesterol.
Sterol O-acyltransferase catalyzes the chemical reaction:
acyl-CoA + cholesterol formula_0 CoA + cholesterol ester
Thus, the two substrates of this enzyme are acyl-CoA and cholesterol, whereas its two products are CoA and cholesteryl ester.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups, the membrane-bound O-acyltransferases. This enzyme participates in bile acid biosynthesis.
Class and structure.
Acyl-CoA cholesterol acyl transferase EC 2.3.1.26, more simply referred to as ACAT, also known as sterol O-acyltransferase (SOAT), belongs to the class of enzymes known as acyltransferases. The role of this enzyme is to transfer fatty acyl groups from one molecule to another. ACAT is an important enzyme in bile acid biosynthesis.
In nearly all mammalian cells, ACAT catalyzes the intracellular esterification of cholesterol and formation of cholesteryl esters. The esterification of cholesterol mediated by ACAT is functionally significant for several reasons. ACAT-mediated esterification of cholesterol limits its solubility in the cell membrane lipids and thus promotes accumulation of cholesterol ester in the fat droplets within cytoplasm; this process is important because the toxic accumulation of free cholesterol in various cell membrane fractions is prevented. Most of the cholesterol absorbed during intestinal transport undergoes ACAT-mediated esterification before incorporation in chylomicrons. In the liver, ACAT-mediated esterification of cholesterol is involved in the production and release of apoB-containing lipoproteins. ACAT also plays an important role in foam cell formation and atherosclerosis by participating in accumulating cholesterol esters in macrophages and vascular tissue. The rate-controlling enzyme in cholesterol catabolism, hepatic cholesterol 7-hydroxylase, is believed to be regulated partly by ACAT.
Mechanism.
The mechanism scheme is as follows:
Acyl-CoA + Cholesterol ←→ CoA + Cholesteryl ester
Isoforms.
There are two isoforms of SOAT (also sometimes referred to as ACAT) that have been reported to date: SOAT1 and SOAT2. SOAT1 is characterized by its ubiquitous presence in tissues with the exception of the intestine, where SOAT2 is prevalent. The different isoforms are also associated with different pathologies associated with abnormalities in lipid metabolism.
SOAT1 (ACAT1).
Previous studies have shown that SOAT modulates proteolytic processing in cell-based and animal models of Alzheimer's disease. A follow-up study reports that SOAT1 RNAi reduced cellular SOAT1 protein and cholesteryl ester levels while causing a slight increase in free cholesterol content of endoplasmic reticulum membranes. The data also showed that a modest decrease in SOAT activity led to suppressive effects on Abeta generation.
SOAT2 (ACAT2).
In a recent study, it was shown that SOAT2 activity is upregulated as a result of chronic renal failure. This study was specific to hepatic SOAT, which plays a major role in hepatic production and release of very low density lipoprotein (VLDL), release of cholesterol, foam cell formation, and atherogenesis.
In another study, non-human primates revealed a positive correlation between liver cholesteryl ester secretion rate and the development of coronal artery atherosclerosis. The results of the experiment are indicative that under all of the conditions of cellular cholesterol availability tested, the relative level of SOAT2 expression affects the cholesteryl ester content, and therefore the atherogenecity of nascent apoB-containing lipoproteins.
Yeast.
In yeast, acyl-CoA:sterol acyltransferase (ASAT) is functionally equivalent to ACAT. Although studies "in vitro" and in yeast suggest that the acyl-CoA binding protein (ACBP) may modulate long-chain fatty acyl-CoA (LCFA-CoA) distribution, the physiological function in mammals is unresolved. Recent research suggests that ACBP expression may play a role in LCFA-CoA metabolism in a physiological context.
In "S. cerevisiae", the accumulation of ergosteryl esters accompanies entry into the stationary phase and sporulation. Researchers have identified two genes in yeast, ARE2 and ARE1, that encode the different isozymes of ASAT. In yeast, Are2 is the major catalytic isoform. Mitotic cell growth and spore germination are not compromised when these genes are deleted, but diploids that are homozygous for an ARE2 null mutation exhibit a decrease in sporulation efficiency.
Plant Synthesis of Steryl Esters.
In plants cellular sterol ester synthesis is performed by an enzyme different from mammalian ACAT and yeast ASAT; it is performed by Phospholipid:Sterol Acyltransferase (PSAT). A recent study shows that PSAT is involved in the regulation of the pool of free sterols and the amount of free sterol intermediates in the membranes. It is also described as the only intracellular enzyme discovered that catalyzes an acyl-CoA independent sterol ester formation. PSAT is therefore considered to have a similar physiological function in plant cells as ACAT in animal cells.
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14544592
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Sulfoacetaldehyde acetyltransferase
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In enzymology, a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) is an enzyme that catalyzes the chemical reaction
acetyl phosphate + sulfite formula_0 2-sulfoacetaldehyde + phosphate
Thus, the two substrates of this enzyme are acetyl phosphate and sulfite, whereas its two products are 2-sulfoacetaldehyde and phosphate.
This enzyme belongs to the family of transferases, specifically those acyltransferases that convert acyl groups into alkyl groups on transfer. The systematic name of this enzyme class is acetyl-phosphate:sulfite S-acetyltransferase (acyl-phosphate hydrolysing, 2-oxoethyl-forming). This enzyme is also called Xsc. This enzyme participates in taurine and hypotaurine metabolism.
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14544600
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Tartronate O-hydroxycinnamoyltransferase
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In enzymology, a tartronate O-hydroxycinnamoyltransferase (EC 2.3.1.106) is an enzyme that catalyzes the chemical reaction
sinapoyl-CoA + 2-hydroxymalonate formula_0 CoA + sinapoyltartronate
Thus, the two substrates of this enzyme are sinapoyl-CoA and 2-hydroxymalonate, whereas its two products are CoA and sinapoyltartronate.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is sinapoyl-CoA:2-hydroxymalonate O-(hydroxycinnamoyl)transferase. Other names in common use include tartronate sinapoyltransferase, and hydroxycinnamoyl-coenzyme-A:tartronate hydroxycinnamoyltransferase.
References.
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14544614
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Taxadien-5alpha-ol O-acetyltransferase
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In enzymology, a taxadien-5alpha-ol O-acetyltransferase (EC 2.3.1.162) is an enzyme that catalyzes the chemical reaction
acetyl-CoA + taxa-4(20),11-dien-5alpha-ol formula_0 CoA + taxa-4(20),11-dien-5alpha-yl acetate
Thus, the two substrates of this enzyme are acetyl-CoA and taxa-4(20),11-dien-5alpha-ol, whereas its two products are CoA and taxa-4(20),11-dien-5alpha-yl acetate.
This enzyme participates in diterpenoid biosynthesis.
Nomenclature.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acetyl-CoA:taxa-4(20),11-dien-5alpha-ol O-acetyltransferase. Other names in common use include acetyl coenzyme A:taxa-4(20),11(12)-dien-5alpha-ol O-acetyl, and transferase.
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14544632
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Tetrahydrodipicolinate N-acetyltransferase
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In enzymology, a tetrahydrodipicolinate N-acetyltransferase (EC 2.3.1.89) is an enzyme that catalyzes the chemical reaction
acetyl-CoA + (S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate + H2O formula_0 CoA + L-2-acetamido-6-oxoheptanedioate
The 3 substrates of this enzyme are acetyl-CoA, (S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate, and H2O, whereas its two products are CoA and L-2-acetamido-6-oxoheptanedioate.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acetyl-CoA:(S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate N2-acetyltransferase. Other names in common use include tetrahydrodipicolinate acetylase, tetrahydrodipicolinate:acetyl-CoA acetyltransferase, acetyl-CoA:L-2,3,4,5-tetrahydrodipicolinate N2-acetyltransferase, acetyl-CoA:(S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate, and 2-N-acetyltransferase. This enzyme participates in lysine biosynthesis.
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14544667
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Trehalose O-mycolyltransferase
|
In enzymology, a trehalose O-mycolyltransferase (EC 2.3.1.122) is an enzyme that catalyzes the chemical reaction
2 alpha,alpha-trehalose 6-mycolate formula_0 alpha,alpha-trehalose + alpha,alpha-trehalose 6,6'-bismycolate
Hence, this enzyme has one substrate( alpha,alpha'-trehalose 6-mycolate) and two products ( alpha,alpha-trehalose and alpha,alpha'-trehalose 6,6'-bismycolate).
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is alpha,alpha-trehalose-6-mycolate:alpha,alpha-trehalose-6-mycolate 6'-mycolyltransferase. Other names in common use include alpha,alpha'-trehalose 6-monomycolate:alpha,alpha'-trehalose, mycolyltransferase, alpha,alpha'-trehalose-6-mycolate:alpha,alpha'-trehalose-6-mycolate, and 6'-mycolyltransferase.
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14544685
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Triacylglycerol—sterol O-acyltransferase
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In enzymology, a triacylglycerol---sterol O-acyltransferase (EC 2.3.1.77) is an enzyme that catalyzes the chemical reaction
triacylglycerol + a 3beta-hydroxysterol formula_0 diacylglycerol + a 3beta-hydroxysterol ester
Thus, the two substrates of this enzyme are triacylglycerol and 3beta-hydroxysterol, whereas its two products are diacylglycerol and 3beta-hydroxysterol ester.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is triacylglycerol:3beta-hydroxysterol O-acyltransferase. This enzyme is also called triacylglycerol:sterol acyltransferase.
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14544699
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Trihydroxystilbene synthase
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In enzymology, a trihydroxystilbene synthase (EC 2.3.1.95) is an enzyme that catalyzes the chemical reaction
3 malonyl-CoA + 4-coumaroyl-CoA formula_0 4 CoA + 3,4',5-trihydroxy-stilbene + 4 CO2
Thus, the two substrates of this enzyme are malonyl-CoA and 4-coumaroyl-CoA, whereas its 3 products are CoA, 3,4',5-trihydroxy-stilbene (resveratrol), and CO2.
This enzyme belongs to the family of transferases, To be specific those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing). Other names in common use include resveratrol synthase, and stilbene synthase. This enzyme participates in phenylpropanoid biosynthesis.
Structural studies.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 1Z1E and 1Z1F.
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14544728
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Tyramine N-feruloyltransferase
|
In enzymology, a tyramine N-feruloyltransferase (EC 2.3.1.110) is an enzyme that catalyzes the chemical reaction
feruloyl-CoA + tyramine formula_0 CoA + N-feruloyltyramine
Thus, the two substrates of this enzyme are feruloyl-CoA and tyramine, whereas its two products are CoA and N-feruloyltyramine.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is feruloyl-CoA:tyramine N-(hydroxycinnamoyl)transferase. Other names in common use include tyramine N-feruloyl-CoA transferase, feruloyltyramine synthase, feruloyl-CoA tyramine N-feruloyl-CoA transferase, and tyramine feruloyltransferase.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14544728
|
14544750
|
UDP-N-acetylmuramoylpentapeptide-lysine N6-alanyltransferase
|
Class of enzymes
In enzymology, an UDP-N-acetylmuramoylpentapeptide-lysine N6-alanyltransferase (EC 2.3.2.10) is an enzyme that catalyzes the chemical reaction
L-alanyl-tRNA + UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysyl-D-alanyl-D-alanine formula_0 tRNA + UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-N6-(L-alanyl)-L-lysyl-D- alanyl-D-alanine
Thus, the two substrates of this enzyme are L-alanyl-tRNA and UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysyl-D-alanyl-D-alanine, whereas its 3 products are tRNA, UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-N6-(L-alanyl)-L-lysyl-D-, and alanyl-D-alanine.
This enzyme belongs to the family of transferases, specifically the aminoacyltransferases. The systematic name of this enzyme class is L-alanyl-tRNA:UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysyl-D-ala nyl-D-alanine N6-alanyltransferase. Other names in common use include alanyl-transfer ribonucleate-uridine, diphosphoacetylmuramoylpentapeptide transferase, UDP-N-acetylmuramoylpentapeptide lysine N6-alanyltransferase, uridine diphosphoacetylmuramoylpentapeptide lysine, N6-alanyltransferase, L-alanyl-tRNA:UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysyl-D-, and alanyl-D-alanine 6-N-alanyltransferase. This enzyme participates in peptidoglycan biosynthesis.
Structural studies.
As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes 1P4N, 1XE4, 1XF8, and 1XIX.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14544750
|
14544773
|
Vinorine synthase
|
In enzymology, a vinorine synthase (EC 2.3.1.160) is an enzyme that catalyzes the chemical reaction
acetyl-CoA + 16-epivellosimine formula_0 CoA + vinorine
Thus, the two substrates of this enzyme are acetyl-CoA and 16-epivellosimine, whereas its two products are CoA and vinorine.
This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acyl-CoA:16-epivellosimine O-acetyltransferase (cyclizing). This enzyme participates in indole and ipecac alkaloid biosynthesis.
Structural studies.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 2BGH.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14544773
|
14545131
|
1-deoxy-D-xylulose-5-phosphate synthase
|
Class of enzymes
In enzymology, a 1-deoxy-d-xylulose-5-phosphate synthase (EC 2.2.1.7) is an enzyme in the non-mevalonate pathway that catalyzes the chemical reaction
pyruvate + d-glyceraldehyde 3-phosphate formula_0 1-deoxy-d-xylulose 5-phosphate + CO2
Thus, the two substrates of this enzyme are pyruvate and d-glyceraldehyde 3-phosphate, whereas its two products are 1-deoxy-d-xylulose 5-phosphate and CO2.
This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). The systematic name of this enzyme class is pyruvate:d-glyceraldehyde-3-phosphate acetaldehydetransferase (decarboxylating). Other names in common use include 1-deoxy-d-xylulose-5-phosphate pyruvate-lyase (carboxylating), and DXP-synthase. This enzyme participates in biosynthesis of steroids.
Structural studies.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2O1S and 2O1X.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545131
|
14545148
|
2-hydroxy-3-oxoadipate synthase
|
Class of enzymes
In enzymology, a 2-hydroxy-3-oxoadipate synthase (EC 2.2.1.5) is an enzyme that catalyzes the following chemical reaction:
2-oxoglutarate + glyoxylate formula_0 2-hydroxy-3-oxoadipate + CO2
The two substrates of this enzyme are 2-oxoglutarate and glyoxylate, whereas its two products are 2-hydroxy-3-oxoadipate and CO2.
This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). Other names in common use include 2-hydroxy-3-oxoadipate glyoxylate-lyase (carboxylating), alpha-ketoglutaric-glyoxylic carboligase, and oxoglutarate: glyoxylate carboligase. This enzyme participates in glyoxylate and dicarboxylate metabolism. It employs one cofactor, thiamin diphosphate.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545148
|
14545175
|
Acetoin—ribose-5-phosphate transaldolase
|
Class of enzymes
In enzymology, an acetoin-ribose-5-phosphate transaldolase (EC 2.2.1.4) is an enzyme that catalyzes the chemical reaction
3-hydroxybutan-2-one + D-ribose 5-phosphate formula_0 acetaldehyde + 1-deoxy-D-altro-heptulose 7-phosphate
Thus, the two substrates of this enzyme are 3-hydroxybutan-2-one and D-ribose 5-phosphate, whereas its two products are acetaldehyde and 1-deoxy-D-altro-heptulose 7-phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). The systematic name of this enzyme class is 3-hydroxybutan-2-one:D-ribose-5-phosphate aldehydetransferase. Other names in common use include 1-deoxy-D-altro-heptulose-7-phosphate synthetase, 1-deoxy-D-altro-heptulose-7-phosphate synthase, 3-hydroxybutan-2-one:D-ribose-5-phosphate aldehydetransferase [wrong, and substrate name]. It employs one cofactor, thiamin diphosphate.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545175
|
14545200
|
Fluorothreonine transaldolase
|
Enzyme
In enzymology, a fluorothreonine transaldolase (EC 2.2.1.8) is an enzyme that catalyzes the chemical reaction
-threonine + fluoroacetaldehyde formula_0 acetaldehyde + 4-fluoro--threonine
Thus, the two substrates of this enzyme are -threonine and fluoroacetaldehyde, whereas its two products are acetaldehyde and 4-fluoro--threonine.
This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). The systematic name of this enzyme class is fluoroacetaldehyde:L-threonine aldehydetransferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545200
|
14545229
|
Formaldehyde transketolase
|
Class of enzymes
In enzymology, a formaldehyde transketolase (EC 2.2.1.3) is an enzyme that catalyzes the chemical reaction
D-xylulose 5-phosphate + formaldehyde formula_0 glyceraldehyde 3-phosphate + glycerone
Thus, the two substrates of this enzyme are D-xylulose 5-phosphate and formaldehyde, whereas its two products are glyceraldehyde 3-phosphate and glycerone.
This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). The systematic name of this enzyme class is D-xylulose-5-phosphate:formaldehyde glycolaldehydetransferase. This enzyme is also called dihydroxyacetone synthase. This enzyme participates in methane metabolism. It employs one cofactor, thiamin diphosphate.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545229
|
1454542
|
Boxcar function
|
In mathematics, a boxcar function is any function which is zero over the entire real line except for a single interval where it is equal to a constant, "A". The function is named after its graph's resemblance to a boxcar, a type of railroad car. The boxcar function can be expressed in terms of the uniform distribution as
formula_0
where "f"("a","b";"x") is the uniform distribution of "x" for the interval ["a", "b"] and formula_1 is the Heaviside step function. As with most such discontinuous functions, there is a question of the value at the transition points. These values are probably best chosen for each individual application.
When a boxcar function is selected as the impulse response of a filter, the result is a simple moving average filter, whose frequency response is a sinc-in-frequency, a type of low-pass filter.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\operatorname{boxcar}(x)= (b-a)A\\,f(a,b;x) = A(H(x-a) - H(x-b)),"
},
{
"math_id": 1,
"text": "H(x)"
}
] |
https://en.wikipedia.org/wiki?curid=1454542
|
14545550
|
3-deoxy-8-phosphooctulonate synthase
|
Enzyme
In enzymology, a 3-deoxy-8-phosphooctulonate synthase (EC 2.5.1.55) is an enzyme that catalyzes the chemical reaction
phosphoenolpyruvate + D-arabinose 5-phosphate + H2O formula_0 2-dehydro-3-deoxy-D-octonate 8-phosphate + phosphate
The 3 substrates of this enzyme are phosphoenolpyruvate, D-arabinose 5-phosphate, and H2O, whereas its two products are 2-dehydro-3-deoxy-D-octonate 8-phosphate and phosphate.
This enzyme participates in lipopolysaccharide biosynthesis.
Nomenclature.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is phosphoenolpyruvate:D-arabinose-5-phosphate C-(1-carboxyvinyl)transferase (phosphate-hydrolysing, 2-carboxy-2-oxoethyl-forming). Other names in common use include 2-dehydro-3-deoxy-D-octonate-8-phosphate, D-arabinose-5-phosphate-lyase (pyruvate-phosphorylating), 2-dehydro-3-deoxy-phosphooctonate aldolase, 2-keto-3-deoxy-8-phosphooctonic synthetase, 3-deoxy-D-manno-octulosonate-8-phosphate synthase, 3-deoxy-D-mannooctulosonate-8-phosphate synthetase, 3-deoxyoctulosonic 8-phosphate synthetase, KDOP synthase, and phospho-2-keto-3-deoxyoctonate aldolase.
References.
<templatestyles src="Reflist/styles.css" />
Further reading.
<templatestyles src="Refbegin/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545550
|
14545618
|
Adenosylmethionine cyclotransferase
|
Class of enzymes
In enzymology, an adenosylmethionine cyclotransferase (EC 2.5.1.4) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine formula_0 5'-methylthioadenosine + 2-aminobutan-4-olide
Hence, this enzyme has one substrate, S-adenosyl-L-methionine, and two products, 5'-methylthioadenosine and 2-aminobutan-4-olide.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosyl-L-methionine alkyltransferase (cyclizing). This enzyme is also called adenosylmethioninase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545618
|
14545632
|
Adenylate dimethylallyltransferase
|
Enzyme
In enzymology, an adenylate dimethylallyltransferase (EC 2.5.1.27) is an enzyme that catalyzes the chemical reaction
dimethylallyl diphosphate + AMP formula_0 diphosphate + N6-(dimethylallyl)adenosine 5'-phosphate
Thus, the two substrates of this enzyme are dimethylallyl diphosphate and AMP, whereas its two products are diphosphate and N6-(dimethylallyl)adenosine 5'-phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:AMP dimethylallyltransferase. Other names in common use include cytokinin synthase, isopentenyltransferase, 2-isopentenyl-diphosphate:AMP Delta2-isopentenyltransferase, and adenylate isopentenyltransferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545632
|
14545643
|
Aspulvinone dimethylallyltransferase
|
Class of enzymes
In enzymology, an aspulvinone dimethylallyltransferase (EC 2.5.1.35) is an enzyme that catalyzes the chemical reaction
2 dimethylallyl diphosphate + aspulvinone E formula_0 2 diphosphate + aspulvinone H
Thus, the two substrates of this enzyme are dimethylallyl diphosphate and aspulvinone E, whereas its two products are diphosphate and aspulvinone H.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:aspulvinone-E dimethylallyltransferase. This enzyme is also called dimethylallyl pyrophosphate:aspulvinone dimethylallyltransferase.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545643
|
14545659
|
Beta-pyrazolylalanine synthase
|
Class of enzymes
In enzymology, a beta-pyrazolylalanine synthase (EC 2.5.1.51) is an enzyme that catalyzes the chemical reaction
O3-acetyl-L-serine + pyrazole formula_0 3-(pyrazol-1-yl)-L-alanine + acetate
Thus, the two substrates of this enzyme are O3-acetyl-L-serine and pyrazole, whereas its two products are 3-(pyrazol-1-yl)-L-alanine and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O3-acetyl-L-serine:pyrazole 1-(2-amino-2-carboxyethyl)transferase. Other names in common use include beta-(1-pyrazolyl)alanine synthase, beta-pyrazolealanine synthase, beta-pyrazolylalanine synthase (acetylserine), O3-acetyl-L-serine acetate-lyase (adding pyrazole), BPA-synthase, pyrazolealanine synthase, pyrazolylalaninase, and 3-O-acetyl-L-serine:pyrazole 1-(2-amino-2-carboxyethyl)transferase.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545659
|
14545692
|
Chlorophyll synthase
|
Class of enzymes
In enzymology, chlorophyll synthase (EC 2.5.1.62) is an enzyme that catalyzes the chemical reaction
chlorophyllide a + phytyl diphosphate formula_0 chlorophyll a + diphosphate
The two substrates of this enzyme are chlorophyllide "a" and phytyl diphosphate; its two products are chlorophyll "a" and diphosphate. The same enzyme can act on chlorophyllide "b" to form chlorophyll "b" and similarly for chlorophyll "d" and "f".
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is chlorophyllide-a:phytyl-diphosphate phytyltransferase. This reaction is the final step of the complete biosynthetic pathway to chlorophylls from glutamic acid.
References.
<templatestyles src="Reflist/styles.css" />
Further reading.
<templatestyles src="Refbegin/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545692
|
14545726
|
Cystathionine gamma-synthase
|
Class of enzymes
In enzymology, a cystathionine gamma-synthase (EC 2.5.1.48) is an enzyme that catalyzes the formation of cystathionine from cysteine and an activated derivative of homoserine, e.g.:
"O"4-succinyl-L-homoserine + L-cysteine formula_0 L-cystathionine + succinate
In microorganisms, the activated substrate of this enzyme is O4-succinyl-L-homoserine or O4-acetyl-L-homoserine. Cystathionine gamma-synthase from plants uses L-homoserine phosphate instead.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O4-succinyl-L-homoserine:L-cysteine S-(3-amino-3-carboxypropyl)transferase. Other names in common use include O-succinyl-L-homoserine succinate-lyase (adding cysteine), O-succinylhomoserine (thiol)-lyase, homoserine O-transsuccinylase, O-succinylhomoserine synthase, O-succinylhomoserine synthetase, cystathionine synthase, cystathionine synthetase, homoserine transsuccinylase, 4-O-succinyl-L-homoserine:L-cysteine, and S-(3-amino-3-carboxypropyl)transferase. This enzyme participates in 4 metabolic pathways: methionine metabolism, cysteine metabolism, selenoamino acid metabolism, and sulfur metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
"text": "\\longrightarrow"
}
] |
https://en.wikipedia.org/wiki?curid=14545726
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14545741
|
Cysteine synthase
|
Class of enzymes
In enzymology, a cysteine synthase (EC 2.5.1.47) is an enzyme that catalyzes the chemical reaction
"O"3-acetyl--serine + hydrogen sulfide formula_0 -cysteine + acetate
Thus, the two substrates of this enzyme are "O"3-acetyl--serine and hydrogen sulfide, whereas its two products are -cysteine and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O3-acetyl-L-serine:hydrogen-sulfide 2-amino-2-carboxyethyltransferase. Other names in common use include O-acetyl-L-serine sulfhydrylase, O-acetyl-L-serine sulfohydrolase, O-acetylserine (thiol)-lyase, O-acetylserine (thiol)-lyase A, O-acetylserine sulfhydrylase, O3-acetyl-L-serine acetate-lyase (adding hydrogen-sulfide), acetylserine sulfhydrylase, cysteine synthetase, S-sulfocysteine synthase, 3-O-acetyl-L-serine:hydrogen-sulfide, and 2-amino-2-carboxyethyltransferase. This enzyme participates in 3 metabolic pathways: cysteine metabolism, selenoamino acid metabolism, and sulfur metabolism. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 12 structures have been solved for this class of enzymes, with PDB accession codes 1O58, 1VE1, 1Y7L, 1Z7W, 1Z7Y, 2BHS, 2BHT, 2EGU, 2ISQ, 2Q3B, 2Q3C, and 2Q3D.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545741
|
14545759
|
Dimethylallylcistransferase
|
Class of enzymes
In enzymology, a dimethylallylcistransferase (EC 2.5.1.28) is an enzyme that catalyzes the chemical reaction
dimethylallyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + neryl diphosphate
Thus, the two substrates of this enzyme are dimethylallyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and neryl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:isopentenyl-diphosphate dimethylallylcistransferase. This enzyme is also called neryl-diphosphate synthase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545759
|
14545778
|
Discadenine synthase
|
Class of enzymes
In enzymology, a discadenine synthase (EC 2.5.1.24) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine + N6-(Delta2-isopentenyl)-adenine formula_0 5'-methylthioadenosine + discadenine
Thus, the two substrates of this enzyme are S-adenosyl-L-methionine and N6-(Delta2-isopentenyl)-adenine, whereas its two products are 5'-methylthioadenosine and discadenine.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosyl-L-methionine:N6-(Delta2-isopentenyl)-adenine 3-(3-amino-3-carboxypropyl)-transferase. Other names in common use include discadenine synthetase, S-adenosyl-L-methionine:6-N-(Delta2-isopentenyl)-adenine, and 3-(3-amino-3-carboxypropyl)-transferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545778
|
14545801
|
Di-trans,poly-cis-decaprenylcistransferase
|
Class of enzymes
In enzymology, a di-trans,poly-cis-decaprenylcistransferase (EC 2.5.1.31) is an enzyme that catalyzes the chemical reaction
di-trans,poly-cis-decaprenyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + di-trans,poly-cis-undecaprenyl diphosphate
Thus, the two substrates of this enzyme are di-trans,poly-cis-decaprenyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and di-trans,poly-cis-undecaprenyl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is di-trans,poly-cis-decaprenyl-diphosphate:isopentenyl-diphosphate undecaprenylcistransferase. Other names in common use include di-trans,poly-cis-undecaprenyl-diphosphate synthase, undecaprenyl-diphosphate synthase, bactoprenyl-diphosphate synthase, UPP synthetase, undecaprenyl diphosphate synthetase, and undecaprenyl pyrophosphate synthetase. This enzyme participates in terpenoid biosynthesis.
Structural studies.
As of late 2007, 15 structures have been solved for this class of enzymes, with PDB accession codes 1F75, 1JP3, 1UEH, 1V7U, 1X06, 1X07, 1X08, 1X09, 2D2R, 2DTN, 2E98, 2E99, 2E9A, 2E9C, and 2E9D.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545801
|
14545827
|
Farnesyltranstransferase
|
Class of enzymes
In enzymology, a farnesyltranstransferase (EC 2.5.1.29) is an enzyme that catalyzes the chemical reaction.
trans,trans-farnesyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + geranylgeranyl diphosphate
Thus, the two substrates of this enzyme are trans,trans-farnesyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and geranylgeranyl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is trans,trans-farnesyl-diphosphate:isopentenyl-diphosphate farnesyltranstransferase. Other names in common use include geranylgeranyl-diphosphate synthase, geranylgeranyl pyrophosphate synthetase, geranylgeranyl-PP synthetase, farnesyltransferase, and geranylgeranyl pyrophosphate synthase. This enzyme participates in biosynthesis of steroids and terpenoid biosynthesis.
This protein may use the morpheein model of allosteric regulation.
Structural studies.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2DH4 and 2Q80.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14545827
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14545858
|
Geranylgeranylglycerol-phosphate geranylgeranyltransferase
|
InterPro Family
In enzymology, a geranylgeranylglycerol-phosphate geranylgeranyltransferase (EC 2.5.1.42) is an enzyme that catalyzes the chemical reaction
geranylgeranyl diphosphate + sn-3-O-(geranylgeranyl)glycerol 1-phosphate formula_0 diphosphate + 2,3-bis-O-(geranylgeranyl)glycerol 1-phosphate
Thus, the two substrates of this enzyme are geranylgeranyl diphosphate and sn-3-O-(geranylgeranyl)glycerol 1-phosphate, whereas its two products are diphosphate and 2,3-bis-O-(geranylgeranyl)glycerol 1-phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl groups or alkyl groups other than methyl groups. The systematic name of this enzyme class is geranylgeranyl diphosphate:sn-3-O-(geranylgeranyl)glycerol 1-phosphate geranylgeranyltransferase. Other names in common use include geranylgeranyloxyglycerol phosphate geranylgeranyltransferase, and geranylgeranyltransferase II.
Structural studies.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2F6U and 2F6X.
References.
<templatestyles src="Reflist/styles.css" />
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[
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https://en.wikipedia.org/wiki?curid=14545858
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14545876
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Geranyltranstransferase
|
In enzymology, a geranyltranstransferase (EC 2.5.1.10) is an enzyme that catalyzes the chemical reaction
geranyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + trans,trans-farnesyl diphosphate
Thus, the two substrates of this enzyme are geranyl diphosphate (a 10 carbon precursor) and isopentenyl diphosphate (a 5 carbon precursor) whereas its two products are diphosphate and trans,trans-farnesyl diphosphate (a 15 carbon product).
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups.
Nomenclature.
The systematic name of this enzyme class is geranyl-diphosphate:isopentenyl-diphosphate geranyltranstransferase. Other names in common use include:
Common abbreviations include: FPS, FDS, FPPS, and FDPS.
Structure.
The structure and mechanism of farnesyl pyrophosphate synthase (FPPS), a type of geranyltranstransferase, is well characterized. FPPS is a ~30 kDa Mg2+ dependent homodimeric enzyme that synthesizes (E, E)-farnesyl pyrophosphate in a successive manner from two equivalents of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP).
FPPS adopts a 3-layered α-helical fold characteristic of many prenyltransferases with 11 helices and flexible loops in between. The centrally located helices (α4 and α8) contain conserved aspartate motifs (DDXXD) that participate in substrate binding and catalysis. Motif aspartate residues, water oxygens, and pyrophosphate coordinate three Mg2+in an octahedral manner. The trinuclear Mg2+ complex is critical for binding DMAPP and stabilizing the pyrophosphate leaving group while the growing hydrocarbon tail wedges into a deep hydrophobic pocket. Site-directed mutagenesis studies have shown that the ultimate length of the isoprenoid product is determined by bulky residues (often phenyalanine) at the hydrophobic pocket's base.
Mechanism.
From crystal structures and kinetic assays, it is believed that FPPS catalyzes the condensation reaction in three concerted steps: (1) Ionization, (2) Condensation, and (3) Elimination.
In the first step, three Mg2+stabilize the anionic leaving group, pyrophosphate, on dimethylallyl pyrophosphate (DMAPP). The loss of pyrophosphate forms dimethylallyl cation. In the second step, the reactive C3-C5 double bond in isopentyl pyrophosphate (IPP) performs a nucleophilic attack on the previously formed dimethylallyl cation. The final step involves pyrophosphate held in the trinuclear Mg2+ center acting as a catalytic base in an elimination reaction to form geranyl pyrophosphate. A second consecutive round of geranyl pyrophosphate ionization, condensation with IPP, and elimination forms farnesyl pyrophosphate.
Function.
Geranyltranstransferases are an evolutionarily conserved class of enzymes in Archaea, Bacteria, and Eukarya that participate in a broad range of biosynthetic pathways including those of cholesterol, porphyrin, carotenoids, ubiquinone, and isoprenoids. Various studies have located FPPS in chloroplasts, mitochondria, cytosol, and peroxisomes.
In cholesterol synthesis, the product, farnesyl pyrophosphate, is consumed in a reductive tail-to-tail condensation with another farnesyl pyrophosphate to form a 30-carbon compound called squalene by squalene synthase. Through several more biosynthetic steps, squalene is transformed into lanosterol, a direct precursor for cholesterol. Notably, sterols control FPPS expression through two cis regulatory factors (an inverted CAAT box and SRE-3) in the proximal FPPS promoter. In plants, porphyrin and carotenoids constitute accessory pigments that help capture light in the photosystems. Ubiquinone is a key electron carrier in the electron transport chain of cellular respiration. Isoprenoids are a large group of compounds that serve as biosynthetic precursors for lipids and hormones.
Farnesyl and geranyl pyrophosphate also serve as precursors for prenylated proteins. Prenylation is a common type of covalent post-translational modification at C-terminal CaaX motifs that allows proteins to localize to membranes or bind to one another. A notable example of the former is the farnesylation of small G-proteins including Ras, CDC42, Rho, and Rac. The attachment of a hydrophobic aliphatic chain as those present in farnesyl or geranylgeranyl groups allows small G-proteins to tether from membranes and carry out effector functions.
Drug targeting.
FPPS is the target of bisphosphonate drugs such as Fosamax (alendronate) and Actonel (risedronate). Bisphosphonate drugs are commonly prescribed for bone diseases including Paget’s disease, osteolytic metastases, and post-menopausal osteoporosis. Bisphosphonate drugs help maintain bone tissue in osteoporotic patients and reduce blood calcium levels in hypercalcemic patients by inhibiting FPPS in bone-reabsorbing osteoclasts. An FPPS-IPP-risendronate ternary complex demonstrated that risendronate binds to the trinuclear Mg2+ complex and interacts with the hydrophobic pocket in a manner similar to DMAPP.
References.
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{
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https://en.wikipedia.org/wiki?curid=14545876
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14545891
|
Homospermidine synthase (spermidine-specific)
|
Class of enzymes
In enzymology, a homospermidine synthase (spermidine-specific) (EC 2.5.1.45) is an enzyme that catalyzes the chemical reaction
spermidine + putrescine formula_0 sym-homospermidine + propane-1,3-diamine
Thus, the two substrates of this enzyme are spermidine and putrescine, whereas its two products are sym-homospermidine and propane-1,3-diamine.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming).
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14545891
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14545917
|
Isonocardicin synthase
|
Class of enzymes
In enzymology, an isonocardicin synthase (EC 2.5.1.38) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine + nocardicin E formula_0 5'-methylthioadenosine + isonocardicin A
Thus, the two substrates of this enzyme are S-adenosyl-L-methionine and nocardicin E, whereas its two products are 5'-methylthioadenosine and isonocardicin A.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosyl-L-methionine:nocardicin-E 3-amino-3-carboxypropyltransferase. This enzyme is also called nocardicin aminocarboxypropyltransferase.
References.
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{
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14545927
|
Lavandulyl diphosphate synthase
|
Class of enzymes
In enzymology, a lavandulyl diphosphate synthase (EC 2.5.1.69) is an enzyme that catalyzes the chemical reaction
2 dimethylallyl diphosphate formula_0 diphosphate + lavandulyl diphosphate
Hence, this enzyme has one substrate, dimethylallyl diphosphate, and two products, diphosphate and lavandulyl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:dimethylallyl-diphosphate dimethylallyltransferase (lavandulyl-diphosphate-forming). This enzyme is also called FDS-5.
References.
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{
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https://en.wikipedia.org/wiki?curid=14545927
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14545946
|
L-mimosine synthase
|
Class of enzymes
In enzymology, a L-mimosine synthase (EC 2.5.1.52) is an enzyme that catalyzes the chemical reaction
O3-acetyl-L-serine + 3,4-dihydroxypyridine formula_0 3-(3,4-dihydroxypyridin-1-yl)-L-alanine + acetate
Thus, the two substrates of this enzyme are O3-acetyl-L-serine and 3,4-dihydroxypyridine, whereas its two products are 3-(3,4-dihydroxypyridin-1-yl)-L-alanine and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O3-acetyl-L-serine:3,4-dihydroxypyridine 1-(2-amino-2-carboxyethyl)transferase. Other names in common use include O3-acetyl-L-serine acetate-lyase (adding 3,4-dihydroxypyridin-1-yl), 3-O-acetyl-L-serine:3,4-dihydroxypyridine, and 1-(2-amino-2-carboxyethyl)transferase.
References.
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{
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https://en.wikipedia.org/wiki?curid=14545946
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14545964
|
N2-(2-carboxyethyl)arginine synthase
|
Enzyme
In enzymology, a N2-(2-carboxyethyl)arginine synthase (EC 2.5.1.66) is an enzyme that catalyzes the chemical reaction
D-glyceraldehyde 3-phosphate + L-arginine formula_0 N2-(2-carboxyethyl)-L-arginine + phosphate
Thus, the two substrates of this enzyme are D-glyceraldehyde 3-phosphate and L-arginine, whereas its two products are N2-(2-carboxyethyl)-L-arginine and phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is glyceraldehyde-3-phosphate:L-arginine N2-(2-hydroxy-3-oxopropyl) transferase (2-carboxyethyl-forming). Other names in common use include CEAS, N2-(2-carboxyethyl)arginine synthetase, CEA synthetase, glyceraldehyde-3-phosphate:L-arginine 2-N-(2-hydroxy-3-oxopropyl), and transferase (2-carboxyethyl-forming). This enzyme participates in clavulanic acid biosynthesis.
Structural studies.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2IHT and 2IHV.
References.
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{
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https://en.wikipedia.org/wiki?curid=14545964
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14545973
|
N-acetylneuraminate synthase
|
Class of enzymes
In enzymology, a N-acetylneuraminate synthase (EC 2.5.1.56) is an enzyme that catalyzes the chemical reaction
phosphoenolpyruvate + N-acetyl-D-mannosamine + H2O formula_0 phosphate + N-acetylneuraminate
The 3 substrates of this enzyme are phosphoenolpyruvate, N-acetyl-D-mannosamine, and H2O, whereas its two products are phosphate and N-acetylneuraminate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is phosphoenolpyruvate:N-acetyl-D-mannosamine C-(1-carboxyvinyl)transferase (phosphate-hydrolysing, 2-carboxy-2-oxoethyl-forming). Other names in common use include (NANA)condensing enzyme, N-acetylneuraminate pyruvate-lyase (pyruvate-phosphorylating), and NeuAc synthase. This enzyme participates in aminosugars metabolism.
Structural studies.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1WVO.
References.
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{
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14545981
|
N-acylneuraminate-9-phosphate synthase
|
Class of enzymes
In enzymology, a N-acylneuraminate-9-phosphate synthase (EC 2.5.1.57) is an enzyme that catalyzes the chemical reaction
phosphoenolpyruvate + N-acyl-D-mannosamine 6-phosphate + H2O formula_0 N-acylneuraminate 9-phosphate + phosphate
The 3 substrates of this enzyme are phosphoenolpyruvate, N-acyl-D-mannosamine 6-phosphate, and H2O, whereas its two products are N-acylneuraminate 9-phosphate and phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is phosphoenolpyruvate:N-acyl-D-mannosamine-6-phosphate 1-(2-carboxy-2-oxoethyl)transferase. Other names in common use include N-acetylneuraminate 9-phosphate lyase, N-acetylneuraminate 9-phosphate sialic acid 9-phosphate synthase, N-acetylneuraminate 9-phosphate synthetase, N-acylneuraminate-9-phosphate pyruvate-lyase, (pyruvate-phosphorylating), and sialic acid 9-phosphate synthetase. This enzyme participates in aminosugars metabolism.
Structural studies.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1WVO.
References.
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{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14545981
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14545999
|
Naringenin 8-dimethylallyltransferase
|
Class of enzymes
In enzymology, a naringenin 8-dimethylallyltransferase (EC 2.5.1.70) is an enzyme that catalyzes the chemical reaction
dimethylallyl diphosphate + (-)-(2S)-naringenin formula_0 diphosphate + sophoraflavanone B
Thus, the two substrates of this enzyme are dimethylallyl diphosphate and (-)-(2S)-naringenin, whereas its two products are diphosphate and sophoraflavanone B.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:naringenin 8-dimethylallyltransferase. This enzyme is also called N8DT.
References.
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{
"math_id": 0,
"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14545999
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14546017
|
Nicotianamine synthase
|
Class of enzymes
In enzymology, a nicotianamine synthase (EC 2.5.1.43) is an enzyme that catalyzes the chemical reaction
3 S-adenosyl-L-methionine formula_0 3 S-methyl-5'-thioadenosine + nicotianamine
Hence, this enzyme has one substrate, S-adenosyl-L-methionine, and two products, S-methyl-5'-thioadenosine and nicotianamine.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosyl-L-methionine:S-adenosyl-L-methionine:S-adenosyl-Lmethioni ne 3-amino-3-carboxypropyltransferase.
References.
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{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14546017
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14546031
|
O-acetylhomoserine aminocarboxypropyltransferase
|
Class of enzymes
In enzymology, an "O"-acetylhomoserine aminocarboxypropyltransferase (EC 2.5.1.49) is an enzyme that catalyzes the chemical reaction
"O"-acetyl--homoserine + methanethiol formula_0 -methionine + acetate
Thus, the two substrates of this enzyme are "O"-acetyl--homoserine and methanethiol, whereas its two products are -methyionine and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O"-acetyl--homoserine:methanethiol 3-amino-3-carboxypropyltransferase. Other names in common use include O"-acetyl--homoserine acetate-lyase (adding methanethiol), O-acetyl--homoserine sulfhydrolase, O"-acetylhomoserine (thiol)-lyase, O"-acetylhomoserine sulfhydrolase, and methionine synthase. This enzyme participates in methionine metabolism and cysteine metabolism.
References.
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{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14546031
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14546042
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O-phosphoserine sulfhydrylase
|
Class of enzymes
In enzymology, an O-phosphoserine sulfhydrylase (EC 2.5.1.65) is an enzyme that catalyzes the chemical reaction
O-phospho-L-serine + hydrogen sulfide formula_0 L-cysteine + phosphate
Thus, the two substrates of this enzyme are O-phospho-L-serine and hydrogen sulfide, whereas its two products are L-cysteine and phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O-phospho-L-serine:hydrogen-sulfide 2-amino-2-carboxyethyltransferase. This enzyme is also called O-phosphoserine(thiol)-lyase. This enzyme participates in cysteine metabolism and sulfur metabolism.
References.
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{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14546042
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14546062
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Phosphoglycerol geranylgeranyltransferase
|
Enzyme
In enzymology, a phosphoglycerol geranylgeranyltransferase (EC 2.5.1.41) is an enzyme that catalyzes the chemical reaction
geranylgeranyl diphosphate + "sn"-glyceryl 1-phosphate formula_0 diphosphate + "sn"-3-"O"-(geranylgeranyl)glyceryl 1-phosphate
Thus, the two substrates of this enzyme are geranylgeranyl diphosphate and "sn"-glyceryl 1-phosphate, whereas its two products are diphosphate and sn-3-O-(geranylgeranyl)glyceryl 1-phosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is geranylgeranyl diphosphate:sn-glyceryl phosphate geranylgeranyltransferase. Other names in common use include glycerol phosphate geranylgeranyltransferase, geranylgeranyl-transferase, and prenyltransferase.
References.
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"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14546062
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14546072
|
Melting-point depression
|
Phenomenon in nanoscale materials
"This article deals with melting/freezing point depression due to very small particle size. For depression due to the mixture of another compound, see freezing-point depression."
Melting-point depression is the phenomenon of reduction of the melting point of a material with a reduction of its size. This phenomenon is very prominent in nanoscale materials, which melt at temperatures hundreds of degrees lower than bulk materials.
Introduction.
The melting temperature of a bulk material is not dependent on its size. However, as the dimensions of a material decrease towards the atomic scale, the melting temperature scales with the material dimensions. The decrease in melting temperature can be on the order of tens to hundreds of degrees for metals with nanometer dimensions.
Melting-point depression is most evident in nanowires, nanotubes and nanoparticles, which all melt at lower temperatures than bulk amounts of the same material. Changes in melting point occur because nanoscale materials have a much larger surface-to-volume ratio than bulk materials, drastically altering their thermodynamic and thermal properties.
Melting-point depression was mostly studied for nanoparticles, owing to their ease of fabrication and theoretical modeling. The melting temperature of a nanoparticle decreases sharply as the particle reaches critical diameter, usually < 50 nm for common engineering metals.
Melting point depression is a very important issue for applications involving nanoparticles, as it decreases the functional range of the solid phase. Nanoparticles are currently used or proposed for prominent roles in catalyst, sensor, medicinal, optical, magnetic, thermal, electronic, and alternative energy applications. Nanoparticles must be in a solid state to function at elevated temperatures in several of these applications.
Measurement techniques.
Two techniques allow measurement of the melting point of the nanoparticle. The electron beam of a transmission electron microscope (TEM) can be used to melt nanoparticles. The melting temperature is estimated from the beam intensity, while changes in the diffraction conditions to indicate phase transition from solid to liquid. This method allows direct viewing of nanoparticles as they melt, making it possible to test and characterize samples with a wider distribution of particle sizes. The TEM limits the pressure range at which melting point depression can be tested.
More recently, researchers developed nanocalorimeters that directly measure the enthalpy and melting temperature of nanoparticles. Nanocalorimeters provide the same data as bulk calorimeters, however, additional calculations must account for the presence of the substrate supporting the particles. A narrow size distribution of nanoparticles is required since the procedure does not allow users to view the sample during the melting process. There is no way to characterize the exact size of melted particles during the experiment.
History.
Melting point depression was predicted in 1909 by Pawlow. It was directly observed inside an electron microscope in the 1960s–70s for nanoparticles of Pb, Au, and In.
Physics.
Nanoparticles have a much greater surface-to-volume ratio than bulk materials. The increased surface-to-volume ratio means surface atoms have a much greater effect on the chemical and physical properties of a nanoparticle. Surface atoms bind in the solid phase with less cohesive energy because they have fewer neighboring atoms in close proximity compared to atoms in the bulk of the solid. Each chemical bond an atom shares with a neighboring atom provides cohesive energy, so atoms with fewer bonds and neighboring atoms have lower cohesive energy. The cohesive energy of the nanoparticle has been theoretically calculated as a function of particle size according to Equation 1.
formula_0
Where: D = nanoparticle size
d = atomic size
Eb = cohesive energy of bulk
As Equation 1 shows, the effective cohesive energy of a nanoparticle approaches that of the bulk material as the material extends beyond the atomic size range (D»d).
Atoms located at or near the surface of the nanoparticle have reduced cohesive energy due to a reduced number of cohesive bonds. An atom experiences an attractive force with all nearby atoms according to the Lennard-Jones potential.
The cohesive energy of an atom is directly related to the thermal energy required to free the atom from the solid. According to Lindemann's criterion, the melting temperature of a material is proportional to its cohesive energy, av (TM=Cav). Since atoms near the surface have fewer bonds and reduced cohesive energy, they require less energy to free from the solid phase. Melting point depression of high surface-to-volume ratio materials results from this effect. For the same reason, surfaces of nanomaterials can melt at lower temperatures than the bulk material.
The theoretical size-dependent melting point of a material can be calculated through classical thermodynamic analysis. The result is the Gibbs–Thomson equation shown in Equation 2.
formula_1
Where: TMB = bulk melting temperature
σsl = solid–liquid interface energy
Hf = Bulk heat of fusion
ρs = density of solid
d = particle diameter
Semiconductor/covalent nanoparticles.
Equation 2 gives the general relation between the melting point of a metal nanoparticle and its diameter. However, recent work indicates the melting point of semiconductor and covalently bonded nanoparticles may have a different dependence on particle size. The covalent character of the bonds changes the melting physics of these materials. Researchers have demonstrated that Equation 3 more accurately models melting point depression in covalently bonded materials.
formula_2
Where: TMB=bulk melting temperature
c=materials constant
d=particle diameter
Equation 3 indicates that melting point depression is less pronounced in covalent nanoparticles due to the quadratic nature of particle size dependence in the melting Equation.
Proposed mechanisms.
The specific melting process for nanoparticles is currently unknown. The scientific community currently accepts several mechanisms as possible models of nanoparticle melting. Each of the corresponding models effectively matches experimental data for the melting of nanoparticles. Three of the four models detailed below derive the melting temperature in a similar form using different approaches based on classical thermodynamics.
Liquid drop model.
The liquid drop model (LDM) assumes that an entire nanoparticle transitions from solid to liquid at a single temperature. This feature distinguishes the model, as the other models predict melting of the nanoparticle surface prior to the bulk atoms. If the LDM is true, a solid nanoparticle should function over a greater temperature range than other models predict. The LDM assumes that the surface atoms of a nanoparticle dominate the properties of all atoms in the particle. The cohesive energy of the particle is identical for all atoms in the nanoparticle.
The LDM represents the binding energy of nanoparticles as a function of the free energies of the volume and surface. Equation 4 gives the normalized, size-dependent melting temperature of a material according to the liquid-drop model.
formula_3
Where: σsv=solid-vapor interface energy
σlv=liquid-vapor interface energy
Hf=Bulk heat of fusion
ρs=density of solid
ρl=density of liquid
d=diameter of nanoparticle
Liquid shell nucleation model.
The liquid shell nucleation model (LSN) predicts that a surface layer of atoms melts prior to the bulk of the particle. The melting temperature of a nanoparticle is a function of its radius of curvature according to the LSN. Large nanoparticles melt at greater temperatures as a result of their larger radius of curvature.
The model calculates melting conditions as a function of two competing order parameters using Landau potentials. One order parameter represents a solid nanoparticle, while the other represents the liquid phase. Each of the order parameters is a function of particle radius.
The parabolic Landau potentials for the liquid and solid phases are calculated at a given temperature, with the lesser Landau potential assumed to be the equilibrium state at any point in the particle. In the temperature range of surface melting, the results show that the Landau curve of the ordered state is favored near the center of the particle while the Landau curve of the disordered state is smaller near the surface of the particle.
The Landau curves intersect at a specific radius from the center of the particle. The distinct intersection of the potentials means the LSN predicts a sharp, unmoving interface between the solid and liquid phases at a given temperature. The exact thickness of the liquid layer at a given temperature is the equilibrium point between the competing Landau potentials.
Equation 5 gives the condition at which an entire nanoparticle melts according to the LSN model.
formula_4
Where: d0=atomic diameter
Liquid nucleation and growth model.
The liquid nucleation and growth model (LNG) treats nanoparticle melting as a surface-initiated process. The surface melts initially, and the liquid-solid interface quickly advances through the entire nanoparticle. The LNG defines melting conditions through the Gibbs-Duhem relations, yielding a melting temperature function dependent on the interfacial energies between the solid and liquid phases, the volumes and surface areas of each phase, and the size of the nanoparticle. The model calculations show that the liquid phase forms at lower temperatures for smaller nanoparticles. Once the liquid phase forms, the free energy conditions quickly change and favor melting. Equation 6 gives the melting conditions for a spherical nanoparticle according to the LNG model.
formula_5
Bond-order-length-strength (BOLS) model.
The bond-order-length-strength (BOLS) model employs an atomistic approach to explain melting point depression. The model focuses on the cohesive energy of individual atoms rather than a classical thermodynamic approach. The BOLS model calculates the melting temperature for individual atoms from the sum of their cohesive bonds. As a result, the BOLS predicts the surface layers of a nanoparticle melt at lower temperatures than the bulk of the nanoparticle.
The BOLS mechanism states that if one bond breaks, the remaining neighbouring ones become shorter and stronger. The cohesive energy, or the sum of bond energy, of the less coordinated atoms determines the thermal stability, including melting, evaporating and other phase transition. The lowered CN changes the equilibrium bond length between atoms near the surface of the nanoparticle. The bonds relax towards equilibrium lengths, increasing the cohesive energy per bond between atoms, independent of the exact form of the specific interatomic potential. However, the integrated, cohesive energy for surface atoms is much lower than for bulk atoms due to the reduced coordination number and an overall decrease in cohesive energy.
Using a core–shell configuration, the melting point depression of nanoparticles is dominated by the outermost two atomic layers, yet atoms in the core interior retain their bulk nature.
The BOLS model and the core–shell structure have been applied to other size dependencies of nanostructures such as the mechanical strength, chemical and thermal stability, lattice dynamics (optical and acoustic phonons), Photon emission and absorption, electronic colevel shift and work function modulation, magnetism at various temperatures, and dielectrics due to electron polarization etc. Reproduction of experimental observations in the above-mentioned size dependency has been realized. Quantitative information, such as the energy level of an isolated atom and the vibration frequency of individual dimer, has been obtained by matching the BOLS predictions to the measured size dependency.
Particle shape.
Nanoparticle shape impacts the melting point of a nanoparticle. Facets, edges and deviations from a perfect sphere all change the magnitude of melting point depression. These shape changes affect the surface -to-volume ratio, which affects the cohesive energy and thermal properties of a nanostructure. Equation 7 gives a general shape-corrected formula for the theoretical melting point of a nanoparticle-based on its size and shape.
formula_6
Where: c=materials constant
z=shape parameter of particle
The shape parameter is 1 for a sphere and 3/2 for a very long wire, indicating that melting-point depression is suppressed in nanowires compared to nanoparticles. Past experimental data show that nanoscale tin platelets melt within a narrow range of 10 °C of the bulk melting temperature. The melting point depression of these platelets was suppressed compared to spherical tin nanoparticles.
Substrate.
Several nanoparticle melting simulations theorize that the supporting substrate affects the extent of melting-point depression of a nanoparticle. These models account for energetic interactions between the substrate materials. A free nanoparticle, as many theoretical models assume, has a different melting temperature (usually lower) than a supported particle due to the absence of cohesive energy between the nanoparticle and substrate. However, measurement of the properties of a freestanding nanoparticle remains impossible, so the extent of the interactions cannot be verified through an experiment. Ultimately, substrates currently support nanoparticles for all nanoparticle applications, so substrate/nanoparticle interactions are always present and must impact melting point depression.
Solubility.
Within the size–pressure approximation, which considers the stress induced by the surface tension and the curvature of the particle, it was shown that the size of the particle affects the composition and temperature of a eutectic point (Fe-C), the solubility of C in Fe and Fe:Mo nanoclusters.
Reduced solubility can affect the catalytic properties of nanoparticles. In fact it, has been shown that size-induced instability of Fe-C mixtures represents the thermodynamic limit for the thinnest nanotube that can be grown from Fe nanocatalysts.
References.
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[
{
"math_id": 0,
"text": "E = E_B(1-\\frac{d}{D})"
},
{
"math_id": 1,
"text": "T_M(d) = T_{MB}(1-\\frac{4\\sigma\\,_{sl}}{H_f\\rho\\,_sd})"
},
{
"math_id": 2,
"text": "T_M(d)=T_{MB}(1-(\\frac{c}{d})^2)"
},
{
"math_id": 3,
"text": "T_M(d)=\\frac{4T_{MB}}{H_fd}\\left(\\sigma\\,_{sv}-\\sigma\\,_{lv}\\left(\\frac{\\rho\\,_s}{\\rho\\,_l}\\right)^{2/3}\\right)"
},
{
"math_id": 4,
"text": "T_M(d)=\\frac{4T_{MB}}{H_fd}(\\frac{\\sigma\\,_{sv}}{1-\\frac{d_0}{d}}-\\sigma\\,_{lv}(1-\\frac{\\rho\\,_s}{\\rho\\,_l}))"
},
{
"math_id": 5,
"text": "T_M(d)=\\frac{2T_{MB}}{H_fd}(\\sigma\\,_{sl}-\\sigma\\,_{lv}3(\\sigma\\,_{sv}-\\sigma\\,_{lv}\\frac{\\rho\\,_s}{\\rho\\,_l}))"
},
{
"math_id": 6,
"text": "T_M(d)=T_{MB}(1-\\frac{c}{zd})"
}
] |
https://en.wikipedia.org/wiki?curid=14546072
|
14546117
|
Protein geranylgeranyltransferase type I
|
Class of enzymes
In enzymology, a protein geranylgeranyltransferase type I (EC 2.5.1.59) is an enzyme that catalyzes the chemical reaction
geranylgeranyl diphosphate + protein-cysteine formula_0 S-geranylgeranyl-protein + diphosphate
Thus, the two substrates of this enzyme are geranylgeranyl diphosphate and protein-cysteine, whereas its two products are S-geranylgeranyl-protein and diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is geranylgeranyl-diphosphate:protein-cysteine geranyltransferase. Other names in common use include GGTase-I, and GGTaseI.
Structural studies.
As of late 2007, 17 structures have been solved for this class of enzymes, with PDB accession codes 1S63, 1S64, 1SA4, 1SA5, 1TNB, 1TNO, 1TNU, 1TNY, 1TNZ, 1X81, 2BED, 2F0Y, 2H6F, 2H6G, 2H6H, 2H6I, and 2IEJ.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546117
|
14546149
|
Rubber cis-polyprenylcistransferase
|
Class of enzymes
In enzymology, a rubber cis-polyprenylcistransferase (EC 2.5.1.20) is an enzyme that catalyzes the chemical reaction
poly-cis-polyprenyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + a poly-cis-polyprenyl diphosphate longer by one C5 unit
Thus, the two substrates of this enzyme are poly-cis-polyprenyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and poly-cis-polyprenyl diphosphate longer by one C5 unit.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is poly-cis-polyprenyl-diphosphate:isopentenyl-diphosphate polyprenylcistransferase. Other names in common use include rubber allyltransferase, rubber transferase, isopentenyl pyrophosphate cis-1,4-polyisoprenyl transferase, cis-prenyl transferase, rubber polymerase, and rubber prenyltransferase. This enzyme participates in biosynthesis of steroids.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546149
|
14546161
|
Sym-norspermidine synthase
|
Class of enzymes
In enzymology, a sym-norspermidine synthase (EC 2.5.1.23) is an enzyme that catalyzes the chemical reaction
S-adenosylmethioninamine + propane-1,3-diamine formula_0 5'-methylthioadenosine + bis(3-aminopropyl)amine
Thus, the two substrates of this enzyme are S-adenosylmethioninamine and propane-1,3-diamine, whereas its two products are 5'-methylthioadenosine and bis(3-aminopropyl)amine.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosylmethioninamine:propane-1,3-diamine 3-aminopropyltransferase. This enzyme participates in urea cycle and metabolism of amino groups.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546161
|
14546178
|
Thiamine-phosphate diphosphorylase
|
Class of enzymes
In enzymology, a thiamine-phosphate diphosphorylase ( or, thiamine-phosphate pyrophosphorylase ) (EC 2.5.1.3) is an enzyme that catalyzes the chemical reaction
4-Amino-5-hydroxymethyl-2-methylpyrimidine diphosphate + 4-methyl-5-(2-phosphono-oxyethyl)thiazole formula_0 diphosphate + thiamine monophosphate
The two substrates of this enzyme are 4-Amino-5-hydroxymethyl-2-methylpyrimidine diphosphate and 4-methyl-5-(2-phosphono-oxyethyl)thiazole; its two products are diphosphate and thiamine monophosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. This enzyme is on the biosynthetic pathway to thiamine.
Nomenclature.
The systematic name of this enzyme class is 2-methyl-4-amino-5-hydroxymethylpyrimidine-diphosphate:4-methyl-5-(2 -phosphoethyl)thiazole 2-methyl-4-aminopyrimidine-5-methenyltransferase. Other names in common use include
Structural studies.
As of late 2007, 9 structures have been solved for this class of enzymes, with PDB accession codes 1G4E, 1G4P, 1G4S, 1G4T, 1G67, 1G69, 1G6C, 1XI3, and 2TPS.
References.
<templatestyles src="Reflist/styles.css" />
Further reading.
<templatestyles src="Refbegin/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546178
|
14546192
|
Heptaprenyl diphosphate synthase
|
Class of enzymes
In enzymology, a heptaprenyl diphosphate synthase (EC 2.5.1.30) is an enzyme that catalyzes the chemical reaction
(2"E",6"E")-farnesyl diphosphate + 4 isopentenyl diphosphate formula_0 4 diphosphate + all-trans-heptaprenyl diphosphate
Thus, the two substrates of this enzyme are (2"E",6"E")-farnesyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and all-trans-heptaprenyl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is (2E,6E)-farnesyl-diphosphate:isopentenyl-diphosphate farnesyltranstransferase (adding 4 isopentenyl units). Other names in common use include all-trans-heptaprenyl-diphosphate synthase, heptaprenyl pyrophosphate synthase, and heptaprenyl pyrophosphate synthetase. This enzyme participates in biosynthesis of steroids.
Structural studies.
As of late 2007, 11 structures have been solved for this class of enzymes, with PDB accession codes 2E8T, 2E8U, 2E8V, 2E8W, 2E8X, 2E90, 2E91, 2E92, 2E93, 2E94, and 2E95.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546192
|
14546261
|
TRNA-uridine aminocarboxypropyltransferase
|
Class of enzymes
In enzymology, a tRNA-uridine aminocarboxypropyltransferase (EC 2.5.1.25) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine + tRNA uridine formula_0 5'-methylthioadenosine + tRNA 3-(3-amino-3-carboxypropyl)-uridine
Thus, the two substrates of this enzyme are S-adenosyl-L-methionine and tRNA uridine, whereas its two products are 5'-methylthioadenosine and tRNA 3-(3-amino-3-carboxypropyl)-uridine.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is S-adenosyl-L-methionine:tRNA-uridine 3-(3-amino-3-carboxypropyl)transferase.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546261
|
14546281
|
Tryptophan dimethylallyltransferase
|
Class of enzymes
In enzymology, a tryptophan dimethylallyltransferase (EC 2.5.1.34) is an enzyme that catalyzes the chemical reaction
dimethylallyl diphosphate + L-tryptophan formula_0 diphosphate + 4-(3-methylbut-2-enyl)-L-tryptophan
Thus, the two substrates of this enzyme are dimethylallyl diphosphate and L-tryptophan, whereas its two products are diphosphate and 4-(3-methylbut-2-enyl)-L-tryptophan.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is dimethylallyl-diphosphate:L-tryptophan dimethylallyltransferase. Other names in common use include dimethylallylpyrophosphate:L-tryptophan dimethylallyltransferase, dimethylallyltryptophan synthetase, dimethylallylpyrophosphate:tryptophan dimethylallyl transferase, DMAT synthetase, and 4-(gamma,gamma-dimethylallyl)tryptophan synthase.
References.
<templatestyles src="Reflist/styles.css" />
|
[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546281
|
14546303
|
UDP-N-acetylglucosamine 1-carboxyvinyltransferase
|
Class of enzymes
In enzymology, an UDP-N-acetylglucosamine 1-carboxyvinyltransferase (EC 2.5.1.7) is an enzyme that catalyzes the first committed step in peptidoglycan biosynthesis of bacteria:
phosphoenolpyruvate + UDP-N-acetyl-D-glucosamine formula_0 phosphate + UDP-N-acetyl-3-O-(1-carboxyvinyl)-D-glucosamine
Thus, the two substrates of this enzyme are phosphoenolpyruvate and UDP-N-acetyl-D-glucosamine, whereas its two products are phosphate and UDP-N-acetyl-3-O-(1-carboxyvinyl)-D-glucosamine. The pyruvate moiety provides the linker that bridges the glycan and peptide portion of peptidoglycan.
The enzyme is inhibited by the antibiotic fosfomycin, which covalently modifies an active site cysteine residue.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is phosphoenolpyruvate:UDP-N-acetyl-D-glucosamine 1-carboxyvinyltransferase. This enzyme participates in amino sugars metabolism and glycan biosynthesis.
Structural studies.
As of late 2007, 10 structures have been solved for this class of enzymes, with PDB accession codes 1A2N, 1DLG, 1EJC, 1EJD, 1EYN, 1NAW, 1Q3G, 1RYW, 1UAE, and 1YBG.
References.
<templatestyles src="Reflist/styles.css" />
Literature.
<templatestyles src="Refbegin/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546303
|
14546316
|
Uracilylalanine synthase
|
Class of enzymes
In enzymology, an uracilylalanine synthase (EC 2.5.1.53) is an enzyme that catalyzes the chemical reaction
O3-acetyl-L-serine + uracil formula_0 3-(uracil-1-yl)-L-alanine + acetate
Thus, the two substrates of this enzyme are O3-acetyl-L-serine and uracil, whereas its two products are 3-(uracil-1-yl)-L-alanine and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O3-acetyl-L-serine:uracil 1-(2-amino-2-carboxyethyl)transferase. Other names in common use include O3-acetyl-L-serine acetate-lyase (adding uracil), isowillardiine synthase, willardiine synthase, and 3-O-acetyl-L-serine:uracil 1-(2-amino-2-carboxyethyl)transferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546316
|
14546336
|
Zeatin 9-aminocarboxyethyltransferase
|
Class of enzymes
In enzymology, a zeatin 9-aminocarboxyethyltransferase (EC 2.5.1.50) is an enzyme that catalyzes the chemical reaction
O-acetyl-L-serine + zeatin formula_0 lupinate + acetate
Thus, the two substrates of this enzyme are O-acetyl-L-serine and zeatin, whereas its two products are lupinate and acetate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O3-acetyl-L-serine:zeatin 2-amino-2-carboxyethyltransferase. Other names in common use include beta-(9-cytokinin)-alanine synthase, beta-(9-cytokinin)alanine synthase, O-acetyl-L-serine acetate-lyase (adding N6-substituted adenine), lupinate synthetase, lupinic acid synthase, lupinic acid synthetase, and 3-O-acetyl-L-serine:zeatin 2-amino-2-carboxyethyltransferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546336
|
14546349
|
Z-farnesyl diphosphate synthase
|
Class of enzymes
In enzymology, a Z-farnesyl diphosphate synthase (EC 2.5.1.68) is an enzyme that catalyzes the chemical reaction
geranyl diphosphate + isopentenyl diphosphate formula_0 diphosphate + (2Z,6E)-farnesyl diphosphate
Thus, the two substrates of this enzyme are geranyl diphosphate and isopentenyl diphosphate, whereas its two products are diphosphate and (2Z,6E)-farnesyl diphosphate.
This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is geranyl-diphosphate:isopentenyl-diphosphate geranylcistransferase. This enzyme is also called (Z)-farnesyl diphosphate synthase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546349
|
14546378
|
Oximinotransferase
|
In enzymology, an oximinotransferase (EC 2.6.3.1) is an enzyme that catalyzes the chemical reaction
pyruvate oxime + acetone formula_0 pyruvate + acetone oxime
Thus, the two substrates of this enzyme are pyruvate oxime and acetone, whereas its two products are pyruvate and acetone oxime.
This enzyme belongs to the family of transferases, specifically those transferring nitrogenous groups oximinotransferases. The systematic name of this enzyme class is pyruvate-oxime:acetone oximinotransferase. Other names in common use include transoximinase, oximase, pyruvate-acetone oximinotransferase, and transoximase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
] |
https://en.wikipedia.org/wiki?curid=14546378
|
14546444
|
Pyridoxine 5'-phosphate synthase
|
Class of enzymes
In enzymology, a pyridoxine 5'-phosphate synthase (EC 2.6.99.2) is an enzyme that catalyzes the chemical reaction
1-deoxy-D-xylulose 5-phosphate + 3-hydroxy-1-aminoacetone phosphate formula_0 pyridoxine-5'-phosphate + phosphate + 2 H2O
The two substrates of this enzyme are 1-deoxy-D-xylulose 5-phosphate (DXP) and 3-hydroxy-1-aminoacetone phosphate (HAP), whereas its 3 products are H2O, phosphate, and pyridoxine-5'-phosphate (a vitamer of pyridoxal phosphate).
Mechanism.
In the first step of this condensation reaction, the amine group of HAP forms a Schiff base with the ketone group of DXP. The hydroxyl group on C4 of DXP is eliminated, forming an enol. The enol eliminates the phosphate derived from DXP, and water is added to the resulting double bond to reform the enol. This enol then attacks the HAP ketone group to close the ring and the resulting hydroxyl group is eliminated to form a double bond. A deprotonation causes the ring to aromatize, completing the synthesis of pyridoxine-5'-phosphate.
3-hydroxy-1-aminoacetone phosphate is unstable, so the reaction mechanism cannot be confirmed directly. Nonetheless, 14C and 18O isotopic labeling experiments, as well as structural studies, support the mechanism shown here. A glutamate residue, Glu72, is positioned ideally to perform most of the acid-base catalysis required in this mechanism, with histidine residues His45 and His193 appearing to play roles as well.
Structure.
Pyridoxine-5'-phosphate synthase, or pdxJ, is a TIM barrel protein, although it exhibits some departures from this motif. Most significantly, the central tunnel of pdxJ is hydrophilic in contrast to the hydrophobic central tunnel observed in most TIM barrel proteins, and pdxJ has three extra alpha helices compared to the classical TIM fold. These three extra helices are important for mediating inter-subunit contacts in the assembled octamer. However, there are also important similarities in function: like many TIM barrel proteins, pdxJ binds its substrates primarily by their phosphate moieties, and the phosphate-binding site responsible for binding to HAP and pyridoxine 5'-phosphate is a conserved motif found in many TIM barrel proteins. The fact that pdxJ binds substrates through their phosphate groups explains a previously discovered specificity for the substrates over their respective non-phosphorylated alcohols.
pdxJ exhibits several different conformations, depending on the substrates or substrate analogs bound. The first state, exhibited when pdxJ has either pyridoxine-5'-phosphate or no substrates bound, is classified as the "open" conformation. This conformation is characterized by an active site freely accessible by solvent. In contrast, when DXP and an HAP analog are bound, loop 4 of the protein folds over the active site, preventing the escape of reaction intermediates or undesirable side reactions. Binding of phosphate alone is not capable of causing a transition between the open and closed states. A third, "partially open" intermediate has also been reported upon binding of DXP alone.
pdxJ assembles as an octamer under biological conditions. This octamer can be thought of as a tetramer of dimers, and it is likely that the dimer is the active unit of the protein. In each dimer, an arginine residue Arg20 forms part of the active site in the other monomer, where it helps bind both phosphate groups.
Classification.
This enzyme belongs to the family of transferases, specifically those transferring nitrogenous groups transferring other nitrogenous groups.
Nomenclature.
The systematic name of this enzyme class is 1-deoxy-D-xylulose-5-phosphate:3-amino-2-oxopropyl phosphate 3-amino-2-oxopropyltransferase (phosphate-hydrolysing; cyclizing). Other names in common use include pyridoxine 5-phosphate phospho lyase, PNP synthase, and PdxJ.
Biological role.
This enzyme participates in vitamin B6 metabolism. pdxJ plays a role in the DXP-dependent pathway of pyridoxal phosphate. The DXP-dependent pathway is found predominantly in Gammaproteobacteria and some Alphaproteobacteria. Because of this distribution, pdxJ has been identified as a potential drug target for antibiotics. This identification seems to have validity, as other approaches have also identified pdxJ as a good target for drug development. However, there may be limits to this approach as pdxJ is not found in obligate parasites. pdxJ and more generally vitamin B6 metabolism in the microbiome have also been shown to alter the effects of certain compounds on animal hosts.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546444
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14546730
|
1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol transaminase
|
Enzyme
In enzymology, a 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol transaminase (EC 2.6.1.56) is an enzyme that catalyzes the chemical reaction
1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol + pyruvate formula_0 1D-1-guanidino-1-deoxy-3-dehydro-scyllo-inositol + L-alanine
Thus, the two substrates of this enzyme are 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol and pyruvate, whereas its two products are 1D-1-guanidino-1-deoxy-3-dehydro-scyllo-inositol and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol:pyruvate aminotransferase. Other names in common use include guanidinoaminodideoxy-scyllo-inositol-pyruvate aminotransferase, and L-alanine-N-amidino-3-(or 5-)keto-scyllo-inosamine transaminase.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546730
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14546740
|
2,5-diaminovalerate transaminase
|
Class of enzymes
In enzymology, a 2,5-diaminovalerate transaminase (EC 2.6.1.8) is an enzyme that catalyzes the chemical reaction
2,5-diaminopentanoate + 2-oxoglutarate formula_0 5-amino-2-oxopentanoate + L-glutamate
Thus, the two substrates of this enzyme are 2,5-diaminopentanoate and 2-oxoglutarate, whereas its two products are 5-amino-2-oxopentanoate and L-glutamate.
It employs one cofactor, pyridoxal phosphate.
Nomenclature.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 2,5-diaminopentanoate:2-oxoglutarate aminotransferase. Other names in common use include diamino-acid transaminase, and diamino acid aminotransferase.
References.
<templatestyles src="Reflist/styles.css" />
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546740
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14546756
|
2-aminoadipate transaminase
|
Class of enzymes
In enzymology, a 2-aminoadipate transaminase (EC 2.6.1.39) is an enzyme that catalyzes the chemical reaction
L-2-aminoadipate + 2-oxoglutarate formula_0 2-oxoadipate + L-glutamate
Thus, the two substrates of this enzyme are L-2-aminoadipate and 2-oxoglutarate, whereas its two products are 2-oxoadipate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-2-aminoadipate:2-oxoglutarate aminotransferase. Other names in common use include alpha-aminoadipate aminotransferase, 2-aminoadipate aminotransferase, 2-aminoadipic aminotransferase, glutamic-ketoadipic transaminase, and glutamate-alpha-ketoadipate transaminase. This enzyme participates in lysine biosynthesis and lysine degradation. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 2DTV.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546756
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14546771
|
2-aminoethylphosphonate—pyruvate transaminase
|
InterPro Family
In enzymology, a 2-aminoethylphosphonate—pyruvate transaminase (EC 2.6.1.37) is an enzyme that catalyzes the chemical reaction
(2-aminoethyl)phosphonate + pyruvate formula_0 2-phosphonoacetaldehyde + L-alanine
Thus, the two substrates of this enzyme are (2-aminoethyl)phosphonate and pyruvate, whereas its two products are 2-phosphonoacetaldehyde and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is (2-aminoethyl)phosphonate:pyruvate aminotransferase. Other names in common use include (2-aminoethyl)phosphonate transaminase, (2-aminoethyl)phosphonate aminotransferase, (2-aminoethyl)phosphonic acid aminotransferase, 2-aminoethylphosphonate-pyruvate aminotransferase, 2-aminoethylphosphonate aminotransferase, 2-aminoethylphosphonate transaminase, AEP transaminase, and AEPT. This enzyme participates in aminophosphonate metabolism. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1M32.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546771
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14546786
|
2-aminohexanoate transaminase
|
Class of enzymes
In enzymology, a 2-aminohexanoate transaminase (EC 2.6.1.67) is an enzyme that catalyzes the chemical reaction
L-2-aminohexanoate + 2-oxoglutarate formula_0 2-oxohexanoate + L-glutamate
Thus, the two substrates of this enzyme are L-2-aminohexanoate and 2-oxoglutarate, whereas its two products are 2-oxohexanoate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-2-aminohexanoate:2-oxoglutarate aminotransferase. Other names in common use include norleucine transaminase, norleucine (leucine) aminotransferase, and leucine L-norleucine: 2-oxoglutarate aminotransferase. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
}
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https://en.wikipedia.org/wiki?curid=14546786
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14546797
|
4-aminobutyrate transaminase
|
Class of enzymes
In enzymology, 4-aminobutyrate transaminase (EC 2.6.1.19), also called GABA transaminase or 4-aminobutyrate aminotransferase, or GABA-T, is an enzyme that catalyzes the chemical reaction:
4-aminobutanoate + 2-oxoglutarate formula_0 succinate semialdehyde + L-glutamate
Thus, the two substrates of this enzyme are 4-aminobutanoate (GABA) and 2-oxoglutarate. The two products are succinate semialdehyde and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 4-aminobutanoate:2-oxoglutarate aminotransferase. This enzyme participates in 5 metabolic pathways: alanine and aspartate metabolism, glutamate metabolism, beta-alanine metabolism, propanoate metabolism, and butanoate metabolism. It employs one cofactor, pyridoxal phosphate.
This enzyme is found in prokaryotes, plants, fungi, and animals (including humans). Pigs have often been used when studying how this protein may work in humans.
Enzyme Commission number.
GABA-T is Enzyme Commission number 2.6.1.19. This means that it is in the transferase class of enzymes, the sub-class and the transaminase sub-subclass. As a nitrogenous transferase, its role is to transfer nitrogenous groups from one molecule to another. As a transaminase, GABA-T's role is to move functional groups from an amino acid and a α-keto acid, and vice versa. In the case of GABA-T, it takes a nitrogen group from GABA and uses it to create L-glutamate.
Reaction pathway.
In animals, fungi, and bacteria, GABA-T helps facilitate a reaction that moves an amine group from GABA to 2-oxoglutarate, and a ketone group from 2-oxoglutarate to GABA. This produces succinate semialdehyde and L-glutamate. In plants, pyruvate and glyoxylate can be used in the place of 2-oxoglutarate. catalyzed by the enzyme 4-aminobutyrate—pyruvate transaminase:
(1) 4-aminobutanoate (GABA) + pyruvate ⇌ succinate semialdehyde + L-alanine
(2) 4-aminobutanoate (GABA) + glyoxylate ⇌ succinate semialdehyde + glycine
Cellular and metabolic role.
The primary role of GABA-T is to break down GABA as part of the GABA-Shunt. In the next step of the shunt, the semialdehyde produced by GABA-T will be oxidized to succinic acid by succinate-semialdehyde dehydrogenase, resulting in succinate. This succinate will then enter mitochondrion and become part of the citric acid cycle. The critic acid cycle can then produce 2-oxoglutarate, which can be used to make glutamate, which can in turn be made into GABA, continuing the cycle.
GABA is a very important neurotransmitter in animal brains, and a low concentration of GABA in mammalian brains has been linked to several neurological disorders, including Alzheimer's disease and Parkinson's disease. Because GABA-T degrades GABA, the inhibition of this enzyme has been the target of many medical studies. The goal of these studies is to find a way to inhibit GABA-T activity, which would reduce the rate that GABA and 2-oxoglutarate are converted to semialdehyde and L-glutamate, thus raising GABA concentration in the brain. There is also a genetic disorder in humans which can lead to a deficiency in GABA-T. This can lead to developmental impairment or mortality in extreme cases.
In plants, GABA can be produced as a stress response. Plants also use GABA to for internal signaling and for interactions with other organisms near the plant. In all of these intra-plant pathways, GABA-T will take on the role of degrading GABA. It has also been demonstrated that the succinate produced in the GABA shunt makes up a significant proportion of the succinate needed by the mitochondrion.
In fungi, the breakdown of GABA in the GABA shunt is key in ensuring a high level of activity in the critic acid cycle. There is also experimental evidence that the breakdown of GABA by GABA-T plays a role in managing oxidative stress in fungi.
Structural Studies.
There have been several structures solved for this class of enzymes, given PDB accession codes, and published in peer-reviewed journals. At least 4 such structures have been solved using pig enzymes: 1OHV, 1OHW, 1OHY, 1SF2, and at least 4 such structures have been solved in "Escherichia coli": 1SFF, 1SZK, 1SZS, 1SZU. There are actually some differences between the enzyme structure for these organisms. "E. coli" enzymes of GABA-T lack an iron-sulfur cluster that is found in the pig model.
Active sites.
Amino acid residues found in the active site of 4-aminobutyrate transaminase include Lys-329, which are found on each of the two subunits of the enzyme. This site will also bind with a pyridoxal 5'- phosphate co-enzyme.
References.
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Further reading.
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https://en.wikipedia.org/wiki?curid=14546797
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14546804
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Terrace ledge kink model
|
In chemistry, the Terrace Ledge Kink model (TLK), which is also referred to as the Terrace Step Kink model (TSK), describes the thermodynamics of crystal surface formation and transformation, as well as the energetics of surface defect formation. It is based upon the idea that the energy of an atom’s position on a crystal surface is determined by its bonding to neighboring atoms and that transitions simply involve the counting of broken and formed bonds. The TLK model can be applied to surface science topics such as crystal growth, surface diffusion, roughening, and vaporization.
History.
The TLK model is credited as having originated from papers published in the 1920s by the German chemist Walther Kossel and the Bulgarian chemist I. N. Stranski
Definitions.
Depending on the position of an atom on a surface, it can be referred to by one of several names. Figure 1 illustrates the names for the atomic positions and point defects on a surface for a simple cubic lattice.
Figure 2 shows a scanning tunneling microscopy topographic image of a step edge that shows many of the features in Figure 1.<br>Figure 3 shows a crystal surface with steps, kinks, adatoms, and vacancies in a closely packed crystalline material, which resembles the surface featured in Figure 2.
Thermodynamics.
The energy required to remove an atom from the surface depends on the number of bonds to other surface atoms which must be broken. For a simple cubic lattice in this model, each atom is treated as a cube and bonding occurs at each face, giving a coordination number of 6 nearest neighbors. Second-nearest neighbors in this cubic model are those that share an edge and third-nearest neighbors are those that share corners. The number of neighbors, second-nearest neighbors, and third-nearest neighbors for each of the different atom positions are given in Table 1.
Most crystals, however, are not arranged in a simple cubic lattice. The same ideas apply for other types of lattices where the coordination number is not six, but these are not as easy to visualize and work with in theory, so the remainder of the discussion will focus on simple cubic lattices. Table 2 indicates the number of neighboring atoms for a bulk atom in some other crystal lattices.
The kink site is of special importance when evaluating the thermodynamics of a variety of phenomena. This site is also referred to as the “half-crystal position” and energies are evaluated relative to this position for processes such as adsorption, surface diffusion, and sublimation. The term “half-crystal” comes from the fact that the kink site has half the number of neighboring atoms as an atom in the crystal bulk, regardless of the type of crystal lattice.
For example, the formation energy for an adatom—ignoring any crystal relaxation—is calculated by subtracting the energy of an adatom from the energy of the kink atom.
This can be understood as the breaking of all of the kink atom’s bonds to remove the atom from the surface and then reforming the adatom interactions. This is equivalent to a kink atom diffusing away from the rest of the step to become a step adatom and then diffusing away from the adjacent step onto the terrace to become an adatom. In the case where all interactions are ignored except for those with nearest neighbors, the formation energy for an adatom would be the following, where formula_0 is the bond energy in the crystal is given by Equation 2.
This can be extended to a variety of situations, such as the formation of an adatom-surface vacancy pair on a terrace, which would involve the removal of a surface atom from the crystal and placing it as an adatom on the terrace. This is described by Equation 3.
The energy of sublimation would simply be the energy required to remove an atom from the kink site. This can be envisioned as the surface being disassembled one terrace at a time by removing atoms from the edge of each step, which is the kink position. It has been demonstrated that the application of an external electric field will induce the formation of additional kinks in a surface, which then leads to a faster rate of evaporation from the surface.
Temperature dependence of defect coverage.
The number of adatoms present on a surface is temperature dependent. The relationship between the surface adatom concentration and the temperature at equilibrium is described by equation 4, where n0 is the total number of surface sites per unit area:
This can be extended to find the equilibrium concentration of other types of surface point defects as well. To do so, the energy of the defect in question is simply substituted into the above equation in the place of the energy of adatom formation.
References.
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14546811
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4-hydroxyglutamate transaminase
|
Class of enzymes
In enzymology, a 4-hydroxyglutamate transaminase (EC 2.6.1.23) is an enzyme that catalyzes the chemical reaction
4-hydroxy-L-glutamate + 2-oxoglutarate formula_0 4-hydroxy-2-oxoglutarate + L-glutamate
Thus, the two substrates of this enzyme are 4-hydroxy-L-glutamate and 2-oxoglutarate, whereas its two products are 4-hydroxy-2-oxoglutarate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 4-hydroxy-L-glutamate:2-oxoglutarate aminotransferase. This enzyme is also called 4-hydroxyglutamate aminotransferase. This enzyme participates in arginine and proline metabolism.
References.
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14546830
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5-aminovalerate transaminase
|
Class of enzymes
In enzymology, a 5-aminovalerate transaminase (EC 2.6.1.48) is an enzyme that catalyzes the chemical reaction
5-aminopentanoate + 2-oxoglutarate formula_0 5-oxopentanoate + L-glutamate
Thus, the two substrates of this enzyme are 5-aminopentanoate and 2-oxoglutarate, whereas its two products are 5-oxopentanoate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 5-aminopentanoate:2-oxoglutarate aminotransferase. Other names in common use include 5-aminovalerate aminotransferase, delta-aminovalerate aminotransferase, and delta-aminovalerate transaminase. This enzyme participates in lysine degradation. It employs one cofactor, pyridoxal phosphate.
References.
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14546846
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Acetylornithine transaminase
|
Class of enzymes
In enzymology, an acetylornithine transaminase (EC 2.6.1.11) is an enzyme that catalyzes the chemical reaction
N2-acetyl-L-ornithine + 2-oxoglutarate formula_0 N-acetyl-L-glutamate 5-semialdehyde + L-glutamate
Thus, the two substrates of this enzyme are N2-acetyl-L-ornithine and 2-oxoglutarate, whereas its two products are N-acetyl-L-glutamate 5-semialdehyde and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is N2-acetyl-L-ornithine:2-oxoglutarate 5-aminotransferase. Other names in common use include acetylornithine delta-transaminase, ACOAT, acetylornithine 5-aminotransferase, acetylornithine aminotransferase, N-acetylornithine aminotransferase, N-acetylornithine-delta-transaminase, N2-acetylornithine 5-transaminase, N2-acetyl-L-ornithine:2-oxoglutarate aminotransferase, succinylornithine aminotransferase, and 2-N-acetyl-L-ornithine:2-oxoglutarate 5-aminotransferase. This enzyme participates in urea cycle and metabolism of amino groups. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes 1VEF, 1WKG, 1WKH, 2E54, 2EH6, and 2ORD.
References.
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https://en.wikipedia.org/wiki?curid=14546846
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14546870
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Adenosylmethionine—8-amino-7-oxononanoate transaminase
|
In enzymology, an adenosylmethionine-8-amino-7-oxononanoate transaminase (EC 2.6.1.62) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine + 8-amino-7-oxononanoate formula_0 S-adenosyl-4-methylthio-2-oxobutanoate + 7,8-diaminononanoate
Thus, the two substrates of this enzyme are S-adenosyl-L-methionine and 8-amino-7-oxononanoate, whereas its two products are S-adenosyl-4-methylthio-2-oxobutanoate and 7,8-diaminononanoate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is S-adenosyl-L-methionine:8-amino-7-oxononanoate aminotransferase. Other names in common use include 7,8-diaminonanoate transaminase, 7,8-diaminononanoate transaminase, DAPA transaminase, 7,8-diaminopelargonic acid aminotransferase, DAPA aminotransferase, 7-keto-8-aminopelargonic acid, diaminopelargonate synthase, and 7-keto-8-aminopelargonic acid aminotransferase. This enzyme participates in biotin metabolism. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 11 structures have been solved for this class of enzymes, with PDB accession codes 1DTY, 1MGV, 1MLY, 1MLZ, 1QJ3, 1QJ5, 1S06, 1S07, 1S08, 1S09, and 1S0A.
References.
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14546886
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Alanine—glyoxylate transaminase
|
In enzymology, an alanine-glyoxylate transaminase (EC 2.6.1.44) is an enzyme that catalyzes the chemical reaction
L-alanine + glyoxylate formula_0 pyruvate + glycine
Thus, the two substrates of this enzyme are L-alanine and glyoxylate, whereas its two products are pyruvate and glycine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-alanine:glyoxylate aminotransferase. Other names in common use include AGT, alanine-glyoxylate aminotransferase, alanine-glyoxylic aminotransferase, and L-alanine-glycine transaminase. This enzyme participates in alanine and aspartate metabolism and glycine, serine and threonine metabolism. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes 1H0C, 1J04, 1VJO, 2BKW, 2HUF, 2HUI, and 2HUU.
References.
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14546904
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Alanine—oxo-acid transaminase
|
Enzyme within the transanimase family
In enzymology, an alanine-oxo-acid transaminase (EC 2.6.1.12) is an enzyme that catalyzes the chemical reaction
L-alanine + a 2-oxo acid formula_0 pyruvate + an L-amino acid
Thus, the two substrates of this enzyme are L-alanine and 2-oxo acid, whereas its two products are pyruvate and L-amino acid.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-alanine:2-oxo-acid aminotransferase. Other names in common use include L-alanine-alpha-keto acid aminotransferase, leucine-alanine transaminase, alanine-keto acid aminotransferase, and alanine-oxo acid aminotransferase. This enzyme participates in alanine and aspartate metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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14546920
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Alanine—oxomalonate transaminase
|
In enzymology, an alanine-oxomalonate transaminase (EC 2.6.1.47) is an enzyme that catalyzes the chemical reaction
L-alanine + oxomalonate formula_0 pyruvate + aminomalonate
Thus, the two substrates of this enzyme are L-alanine and oxomalonate, whereas its two products are pyruvate and aminomalonate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-alanine:oxomalonate aminotransferase. Other names in common use include alanine-oxomalonate aminotransferase, L-alanine-ketomalonate transaminase, and alanine-ketomalonate (mesoxalate) transaminase. It employs one cofactor, pyridoxal phosphate.
References.
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14548330
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Dark star (dark matter)
|
Hypothetical astronomical object heated by dark-matter annihilation
A dark star is a hypothetical type of star that may have existed early in the universe before conventional stars were able to form and thrive.
Properties.
The dark stars would be composed mostly of normal matter, like modern stars, but a high concentration of neutralino dark matter present within them would generate heat via annihilation reactions between the dark-matter particles. This heat would prevent such stars from collapsing into the relatively compact and dense sizes of modern stars and therefore prevent nuclear fusion among the 'normal' matter atoms from being initiated.
Under this model, a dark star is predicted to be an enormous cloud of molecular hydrogen and helium ranging between 1 and 960 astronomical units (AU) in radius; its surface temperature would be around 10000 K. It is expected that they would grow over time and reach masses up to formula_0M☉, up until the point where they exhaust the dark matter needed to sustain them, after which they would collapse.
In the unlikely event that dark stars have endured to the modern era, they could be detectable by their emissions of gamma rays, neutrinos, and antimatter and would be associated with clouds of cold molecular hydrogen gas that normally would not harbor such energetic, extreme, and rare particles.
Possible dark star candidates.
In April 2023, a study investigated four extremely redshifted objects discovered by the James Webb Space Telescope. Their study suggested that three of these four, namely JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0, are consistent with being point sources, and further suggested that the only point sources which could exist in this time and be bright enough to be observed at these phenomenal distances and redshifts (z = 10–13) were supermassive dark stars in the early universe, powered by dark matter annihilation. Their spectral analysis of the objects suggested that they were between 500,000 and 1 million solar masses (M☉), as well as having a luminosity of billions of Suns (L☉); they would also likely be huge, possibly with radii surpassing 10,000 solar radii (R☉), far exceeding the size of the largest modern stars.
References.
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Further reading.
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14548764
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Aminolevulinate transaminase
|
In enzymology, an aminolevulinate transaminase (EC 2.6.1.43) is an enzyme that catalyzes the chemical reaction
5-aminolevulinate + pyruvate formula_0 4,5-dioxopentanoate + L-alanine
Thus, the two substrates of this enzyme are 5-aminolevulinate and pyruvate, whereas its two products are 4,5-dioxopentanoate and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 5-aminolevulinate:pyruvate aminotransferase. Other names in common use include aminolevulinate aminotransferase, gamma,delta-dioxovalerate, aminotransferase, gamma,delta-dioxovaleric acid transaminase, 4,5-dioxovalerate aminotransferase, 4,5-dioxovaleric acid transaminase, 4,5-dioxovaleric transaminase, 5-aminolevulinic acid transaminase, alanine-gamma,delta-dioxovalerate aminotransferase, alanine-dioxovalerate aminotransferase, alanine:4,5-dioxovalerate aminotransferase, aminolevulinic acid transaminase, dioxovalerate transaminase, L-alanine-4,5-dioxovalerate aminotransferase, L-alanine:4,5-dioxovaleric acid transaminase, L-alanine:dioxovalerate transaminase, DOVA transaminase, and 4,5-dioxovaleric acid aminotransferase. This enzyme participates in porphyrin and chlorophyll metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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14548780
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Arginine—pyruvate transaminase
|
In enzymology, an arginine-pyruvate transaminase (EC 2.6.1.84) is an enzyme that catalyzes the chemical reaction
L-arginine + pyruvate formula_0 5-guanidino-2-oxopentanoate + L-alanine
Thus, the two substrates of this enzyme are L-arginine and pyruvate, whereas its two products are 5-guanidino-2-oxopentanoate and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-arginine:pyruvate aminotransferase. Other names in common use include arginine:pyruvate transaminase, and AruH.
References.
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14548793
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Aromatic-amino-acid—glyoxylate transaminase
|
In enzymology, an aromatic-amino-acid-glyoxylate transaminase (EC 2.6.1.60) is an enzyme that catalyzes the chemical reaction
an aromatic amino acid + glyoxylate formula_0 an aromatic oxo acid + glycine
Thus, the two substrates of this enzyme are aromatic amino acid and glyoxylate, whereas its two products are aromatic oxo acid and glycine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is aromatic-amino-acid:glyoxylate aminotransferase.
References.
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14548806
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Aromatic-amino-acid transaminase
|
In enzymology, an aromatic-amino-acid transaminase (EC 2.6.1.57) is an enzyme that catalyzes the chemical reaction
an aromatic amino acid + 2-oxoglutarate formula_0 an aromatic oxo acid + L-glutamate
Thus, the two substrates of this enzyme are aromatic amino acid and 2-oxoglutarate, whereas its two products are aromatic oxo acid and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is aromatic-amino-acid:2-oxoglutarate aminotransferase. Other names in common use include aromatic amino acid aminotransferase, aromatic aminotransferase, and ArAT. This enzyme participates in 6 metabolic pathways: methionine metabolism, tyrosine metabolism, phenylalanine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, novobiocin biosynthesis, and alkaloid biosynthesis i. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 13 structures have been solved for this class of enzymes, with PDB accession codes 1AY4, 1AY5, 1AY8, 2AY1, 2AY2, 2AY3, 2AY4, 2AY5, 2AY6, 2AY7, 2AY8, 2AY9, and 3TAT.
References.
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14548827
|
Asparagine—oxo-acid transaminase
|
In enzymology, an asparagine-oxo-acid transaminase (EC 2.6.1.14) is an enzyme that catalyzes the chemical reaction
L-asparagine + a 2-oxo acid formula_0 2-oxosuccinamate + an amino acid
Thus, the two substrates of this enzyme are L-asparagine and 2-oxo acid, whereas its two products are 2-oxosuccinamate and amino acid.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-asparagine:2-oxo-acid aminotransferase. This enzyme is also called asparagine-keto acid aminotransferase. This enzyme participates in alanine and aspartate metabolism and tetracycline biosynthesis. It employs one cofactor, pyridoxal phosphate.
References.
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14548848
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Aspartate—phenylpyruvate transaminase
|
In enzymology, an aspartate-phenylpyruvate transaminase (EC 2.6.1.70) is an enzyme that catalyzes the chemical reaction
L-aspartate + phenylpyruvate formula_0 oxaloacetate + L-phenylalanine
Thus, the two substrates of this enzyme are L-aspartate and phenylpyruvate, whereas its two products are oxaloacetate and L-phenylalanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-aspartate:phenylpyruvate aminotransferase. This enzyme is also called aspartate-phenylpyruvate aminotransferase.
References.
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14548861
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Aspartate—prephenate aminotransferase
|
In enzymology, an aspartate-prephenate aminotransferase (EC 2.6.1.78) is an enzyme that catalyzes the chemical reaction
L-arogenate + oxaloacetate formula_0 prephenate + L-aspartate
Thus, the two substrates of this enzyme are L-arogenate and oxaloacetate, whereas its two products are prephenate and L-aspartate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-arogenate:oxaloacetate aminotransferase. Other names in common use include prephenate transaminase (ambiguous), PAT (ambiguous), prephenate aspartate aminotransferase, and L-aspartate:prephenate aminotransferase.
References.
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14548883
|
Beta-alanine—pyruvate transaminase
|
Enzyme
In enzymology, a beta-alanine-pyruvate transaminase (EC 2.6.1.18) is an enzyme that catalyzes the chemical reaction
L-alanine + 3-oxopropanoate formula_0 pyruvate + beta-alanine
Thus, the two substrates of this enzyme are L-alanine and 3-oxopropanoate, whereas its two products are pyruvate and beta-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-alanine:3-oxopropanoate aminotransferase. Other names in common use include beta-alanine-pyruvate aminotransferase, and beta-alanine-alpha-alanine transaminase. This enzyme participates in 4 metabolic pathways: alanine and aspartate metabolism, valine, leucine and isoleucine degradation, beta-alanine metabolism, and propanoate metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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14548905
|
Cephalosporin-C transaminase
|
In enzymology, a cephalosporin-C transaminase (EC 2.6.1.74) is an enzyme that catalyzes the chemical reaction
(7R)-7-(5-carboxy-5-oxopentanoyl)aminocephalosporinate + D-glutamate formula_0 cephalosporin C + 2-oxoglutarate
Thus, the two substrates of this enzyme are (7R)-7-(5-carboxy-5-oxopentanoyl)aminocephalosporinate and D-glutamate, whereas its two products are cephalosporin C and 2-oxoglutarate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is cephalosporin-C:2-oxoglutarate aminotransferase. Other names in common use include cephalosporin C aminotransferase, and L-alanine:cephalosporin-C aminotransferase. This enzyme participates in penicillin and cephalosporin biosynthesis.
References.
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[
{
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https://en.wikipedia.org/wiki?curid=14548905
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14548917
|
Cysteine-conjugate transaminase
|
In enzymology, a cysteine-conjugate transaminase (EC 2.6.1.75) is an enzyme that catalyzes the chemical reaction
S-(4-bromophenyl)-L-cysteine + 2-oxoglutarate formula_0 S-(4-bromophenyl)mercaptopyruvate + L-glutamate
Thus, the two substrates of this enzyme are S-(4-bromophenyl)-L-cysteine and 2-oxoglutarate, whereas its two products are S-(4-bromophenyl)mercaptopyruvate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is S-(4-bromophenyl)-L-cysteine:2-oxoglutarate aminotransferase. Other names in common use include cysteine conjugate aminotransferase, and cysteine-conjugate alpha-ketoglutarate transaminase (CAT-1).
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14548917
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14548930
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Cysteine transaminase
|
In enzymology, a cysteine transaminase (EC 2.6.1.3) is an enzyme that catalyzes the chemical reaction
L-cysteine + 2-oxoglutarate formula_0 mercaptopyruvate + L-glutamate
Thus, the two substrates of this enzyme are L-cysteine and 2-oxoglutarate, whereas its two products are mercaptopyruvate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-cysteine:2-oxoglutarate aminotransferase. Other names in common use include cysteine aminotransferase, L-cysteine aminotransferase, and CGT. This enzyme participates in cysteine metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14548930
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14548942
|
D-4-hydroxyphenylglycine transaminase
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In enzymology, a D-4-hydroxyphenylglycine transaminase (EC 2.6.1.72) is an enzyme that catalyzes the chemical reaction
D-4-hydroxyphenylglycine + 2-oxoglutarate formula_0 4-hydroxyphenylglyoxylate + L-glutamate
Thus, the two substrates of this enzyme are D-4-hydroxyphenylglycine and 2-oxoglutarate, whereas its two products are 4-hydroxyphenylglyoxylate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is D-4-hydroxyphenylglycine:2-oxoglutarate aminotransferase. This enzyme is also called D-hydroxyphenylglycine aminotransferase. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
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"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14548942
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14548953
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D-amino-acid transaminase
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In enzymology, a D-amino-acid transaminase (EC 2.6.1.21) is an enzyme that catalyzes the chemical reaction:
D-alanine + 2-oxoglutarate formula_0 pyruvate + D-glutamate
Thus, the two substrates of this enzyme are D-alanine and 2-oxoglutarate, whereas its two products are pyruvate and D-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is D-alanine:2-oxoglutarate aminotransferase. Other names in common use include D-aspartate transaminase, D-alanine aminotransferase, D-aspartic aminotransferase, D-alanine-D-glutamate transaminase, D-alanine transaminase, and D-amino acid aminotransferase. This enzyme participates in 6 metabolic pathways: lysine degradation, arginine and proline metabolism, phenylalanine metabolism, D-arginine and D-ornithine metabolism, D-alanine metabolism, and peptidoglycan biosynthesis. It employs one cofactor, pyridoxal phosphate.
Structural studies.
As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes 1A0G, 1DAA, 1G2W, 2DAA, 2DAB, 3DAA, 4DAA, and 5DAA.
References.
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[
{
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https://en.wikipedia.org/wiki?curid=14548953
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14548974
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Diamine transaminase
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In enzymology, a diamine transaminase (EC 2.6.1.29) is an enzyme that catalyzes the chemical reaction:
an alpha,omega-diamine + 2-oxoglutarate formula_0 an omega-aminoaldehyde + L-glutamate
Thus, the two substrates of this enzyme are alpha,omega-diamine and 2-oxoglutarate, whereas its two products are omega-aminoaldehyde and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is diamine:2-oxoglutarate aminotransferase. Other names in common use include amine transaminase, amine-ketoacid transaminase, diamine aminotransferase, and diamine-ketoglutaric transaminase. This enzyme participates in urea cycle and metabolism of amino groups.
References.
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[
{
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https://en.wikipedia.org/wiki?curid=14548974
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14548991
|
Diaminobutyrate—2-oxoglutarate transaminase
|
In enzymology, a diaminobutyrate-2-oxoglutarate transaminase (EC 2.6.1.76) is an enzyme that catalyzes the chemical reaction
L-2,4-diaminobutanoate + 2-oxoglutarate formula_0 L-aspartate 4-semialdehyde + L-glutamate
Thus, the two substrates of this enzyme are L-2,4-diaminobutanoate and 2-oxoglutarate, whereas its two products are L-aspartate 4-semialdehyde and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-2,4-diaminobutanoate:2-oxoglutarate 4-aminotransferase. Other names in common use include L-2,4-diaminobutyrate:2-ketoglutarate 4-aminotransferase, 2,4-diaminobutyrate 4-aminotransferase, diaminobutyrate aminotransferase, DABA aminotransferase, DAB aminotransferase, EctB, diaminibutyric acid aminotransferase, and L-2,4-diaminobutyrate:2-oxoglutarate 4-aminotransferase. This enzyme participates in glycine, serine and threonine metabolism.
References.
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[
{
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https://en.wikipedia.org/wiki?curid=14548991
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14549003
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Diaminobutyrate—pyruvate transaminase
|
In enzymology, a diaminobutyrate-pyruvate transaminase (EC 2.6.1.46) is an enzyme that catalyzes the chemical reaction
L-2,4-diaminobutanoate + pyruvate formula_0 L-aspartate 4-semialdehyde + L-alanine
Thus, the two substrates of this enzyme are L-2,4-diaminobutanoate and pyruvate, whereas its two products are L-aspartate 4-semialdehyde and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-2,4-diaminobutanoate:pyruvate aminotransferase. Other names in common use include diaminobutyrate-pyruvate aminotransferase, and L-diaminobutyric acid transaminase. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14549003
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14549019
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Dihydroxyphenylalanine transaminase
|
In enzymology, a dihydroxyphenylalanine transaminase (EC 2.6.1.49) is an enzyme that catalyzes the chemical reaction
3,4-dihydroxy-L-phenylalanine + 2-oxoglutarate formula_0 3,4-dihydroxyphenylpyruvate + L-glutamate
Thus, the two substrates of this enzyme are 3,4-dihydroxy-L-phenylalanine and 2-oxoglutarate, whereas its two products are 3,4-dihydroxyphenylpyruvate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 3,4-dihydroxy-L-phenylalanine:2-oxoglutarate aminotransferase. Other names in common use include dopa transaminase, dihydroxyphenylalanine aminotransferase, aspartate-DOPP transaminase (ADT), L-dopa transaminase, dopa aminotransferase, glutamate-DOPP transaminase (GDT), phenylalanine-DOPP transaminase (PDT), DOPA 2-oxoglutarate aminotransferase, and DOPAATS. This enzyme participates in tyrosine metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14549019
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14549033
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Diiodotyrosine transaminase
|
In enzymology, a diiodotyrosine transaminase (EC 2.6.1.24) is an enzyme that catalyzes the chemical reaction
3,5-diiodo-L-tyrosine + 2-oxoglutarate formula_0 4-hydroxy-3,5-diiodophenylpyruvate + L-glutamate
Thus, the two substrates of this enzyme are 3,5-diiodo-L-tyrosine and 2-oxoglutarate, whereas its two products are 4-hydroxy-3,5-diiodophenylpyruvate and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is 3,5-diiodo-L-tyrosine:2-oxoglutarate aminotransferase. Other names in common use include diiodotyrosine aminotransferase, halogenated tyrosine aminotransferase, and halogenated tyrosine transaminase. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
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https://en.wikipedia.org/wiki?curid=14549033
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14549055
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D-methionine—pyruvate transaminase
|
In enzymology, a D-methionine—pyruvate transaminase (EC 2.6.1.41) is an enzyme that catalyzes the chemical reaction
D-methionine + pyruvate formula_0 4-methylthio-2-oxobutanoate + L-alanine
Thus, the two substrates of this enzyme are D-methionine and pyruvate, whereas its two products are 4-methylthio-2-oxobutanoate and L-alanine.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is D-methionine:pyruvate aminotransferase. Other names in common use include D-methionine transaminase, and D-methionine aminotransferase. This enzyme participates in d-alanine metabolism.
References.
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[
{
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https://en.wikipedia.org/wiki?curid=14549055
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14549068
|
DTDP-4-amino-4,6-dideoxy-D-glucose transaminase
|
In enzymology, a dTDP-4-amino-4,6-dideoxy-D-glucose transaminase (EC 2.6.1.33) is an enzyme that catalyzes the chemical reaction
dTDP-4-amino-4,6-dideoxy-D-glucose + 2-oxoglutarate formula_0 dTDP-4-dehydro-6-deoxy-D-glucose + L-glutamate
Thus, the two substrates of this enzyme are dTDP-4-amino-4,6-dideoxy-D-glucose and 2-oxoglutarate, whereas its two products are dTDP-4-dehydro-6-deoxy-D-glucose and L-glutamate.
This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is dTDP-4-amino-4,6-dideoxy-D-glucose:2-oxoglutarate aminotransferase. Other names in common use include thymidine diphospho-4-amino-4,6-dideoxyglucose aminotransferase, thymidine diphospho-4-amino-6-deoxyglucose aminotransferase, thymidine diphospho-4-keto-6-deoxy-D-glucose transaminase, thymidine diphospho-4-keto-6-deoxy-D-glucose-glutamic transaminase, and TDP-4-keto-6-deoxy-D-glucose transaminase. This enzyme participates in nucleotide sugars metabolism. It employs one cofactor, pyridoxal phosphate.
References.
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[
{
"math_id": 0,
"text": "\\rightleftharpoons"
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https://en.wikipedia.org/wiki?curid=14549068
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