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Citric acid cycle
Substrater
Produkter
Enzym
Reaktionstype
Kommentar


0 / 10
Oxaloacetat +
Acetyl CoA +
H2O
Citrat +
CoA-SH
Citrat-syntase
Aldolkondensation
irreversibel,
forlænger 4C-oxaloacetat til et 6C-molekyle


1
Citrat
cis-Aconitat +
H2O
Aconitase
Dehydrering
reversibel isomerisering


2
cis-konitat +
H2O
Isocitrat
Hydrering


3
Isocitrat +
NAD+
Oxalosuccinat +
NADH + H +
Isocitratdehydrogenase
Oxidation
danner NADH (svarende til 2,5 ATP)


4
Oxalosuccinat
α-Ketoglutarat +
CO2
Decarboxylering
hastighedsbegrænsende, irreversibel fase,
danner et 5C-molekyle


5
α-Ketoglutarat +
NAD+ + +
CoA-SH
Succinyl-CoA +
NADH + H+ +
CO2
α-Ketoglutarat-dehydrogenase
Oxidativ
decarboxylering
irreversibel fase,
genererer NADH (svarende til 2,5 ATP),
regenererer 4C-kæden (CoA udelukket)


6
Succinyl-CoA +
GDP + Pi
Succinat +
CoA-SH +
GTP
Succinyl-CoA-syntetase
fosforylering på substratniveau
eller ADP→ATP i stedet for GDP→GTP,
genererer 1 ATP eller tilsvarende
Kondensationsreaktion af GDP + Pi og hydrolyse af Succinyl-CoA involverer det H2O, der er nødvendigt for den afbalancerede ligning.



7
Succinat +
ubiquinon (Q)
Fumarat +
ubiquinol (QH2)
Succinatdehydrogenase
Oxidation
bruger FAD som en prostetisk gruppe (FAD→FADH2 i reaktionens første trin) i enzymet. disse to elektroner overføres senere til QH2 i ETC's kompleks II, hvor de
genererer det, der svarer til 1,5 ATP


8
Fumarat +
H2O
L-malat
Fumarase
Hydrering
Hydrering af C-C-dobbeltbinding


9
L-malat +
NAD+
Oxaloacetat +
NADH + H+
Malatdehydrogenase
Oxidation
reversibel (faktisk er ligevægten til fordel for malat), genererer NADH (svarende til 2,5 ATP)


10 / 0
Oxaloacetat +
Acetyl CoA +
H2O
Citrat +
CoA-SH
Citrat-syntase
Aldolkondensation
Dette er det samme som trin 0 og genstarter cyklussen. Reaktionen er irreversibel og forlænger 4C-oxaloacetatet til et 6C-molekyle
Citric acid cycle
Substrates
Products
Enzyme
Reaction type
Comment


0 / 10
Oxaloacetate +
Acetyl CoA +
H2O
Citrate +
CoA-SH
Citrate synthase
Aldol condensation
irreversible,
extends the 4C oxaloacetate to a 6C molecule


1
Citrate
cis-Aconitate +
H2O
Aconitase
Dehydration
reversible isomerisation


2
cis-Aconitate +
H2O
Isocitrate
Hydration


3
Isocitrate +
NAD+
Oxalosuccinate +
NADH + H +
Isocitrate dehydrogenase
Oxidation
generates NADH (equivalent of 2.5 ATP)


4
Oxalosuccinate
α-Ketoglutarate +
CO2
Decarboxylation
rate-limiting, irreversible stage,
generates a 5C molecule


5
α-Ketoglutarate +
NAD+ +
CoA-SH
Succinyl-CoA +
NADH + H+ +
CO2
α-Ketoglutarate dehydrogenase
Oxidative
decarboxylation
irreversible stage,
generates NADH (equivalent of 2.5 ATP),
regenerates the 4C chain (CoA excluded)


6
Succinyl-CoA +
GDP + Pi
Succinate +
CoA-SH +
GTP
Succinyl-CoA synthetase
substrate-level phosphorylation
or ADP→ATP instead of GDP→GTP,
generates 1 ATP or equivalent
Condensation reaction of GDP + Pi and hydrolysis of Succinyl-CoA involve the H2O needed for balanced equation.



7
Succinate +
ubiquinone (Q)
Fumarate +
ubiquinol (QH2)
Succinate dehydrogenase
Oxidation
uses FAD as a prosthetic group (FAD→FADH2 in the first step of the reaction) in the enzyme.These two electrons are later transferred to QH2 during Complex II of the ETC, where they
generate the equivalent of 1.5 ATP


8
Fumarate +
H2O
L-Malate
Fumarase
Hydration
Hydration of C-C double bond


9
L-Malate +
NAD+
Oxaloacetate +
NADH + H+
Malate dehydrogenase
Oxidation
reversible (in fact, equilibrium favors malate), generates NADH (equivalent of 2.5 ATP)


10 / 0
Oxaloacetate +
Acetyl CoA +
H2O
Citrate +
CoA-SH
Citrate synthase
Aldol condensation
This is the same as step 0 and restarts the cycle. The reaction is irreversible and extends the 4C oxaloacetate to a 6C molecule
Citric acid cycle