Adenylyl-sulfate reductase (thioredoxin) () is an enzyme that catalyzes the chemical reaction AMP + sulfite + thioredoxin disulfide 5'-adenylyl sulfate + thioredoxin The 3 substrates of this enzyme are adenosine monophosphate, sulfite, and thioredoxin disulfide, whereas its two products are 5'-adenylyl sulfate and thioredoxin. This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with a disulfide as acceptor. This enzyme also assists a feature of the Calvin-Benson cycle's light regulation within the ferredoxin-thioredoxin system in the form of reduced thioredoxin. Thioredoxin-type adenylyl-sulfate reductase also uses thioredoxin as an electron donor in reactions related to protein synthesis. Note this is a general pathway and other resemblances are studied in literature to support this. The enzyme functions in reactions that in the end stabilize Thiols in related bonds that end up forming a dithiol group as a byproduct. Nomenclature The systematic name of this enzyme class is AMP, sulfite:thioredoxin-disulfide oxidoreductase (adenosine-5'-phosphosulfate-forming). This enzyme is also called thioredoxin-dependent 5'-adenylylsulfate reductase. Classication This enzyme (Adenylyl-sulfate reductase) is an oxidoreductase (Class 1) or more specifically a sulfur oxidoreductase (Sub-Class 8) disulfide (Sub-Subclass 4). The enzyme bears the serial number of 10 under the EC naming system. The primary difference that this particular adenylyl-sulfate reductase from others is it uses thioredoxin as an electron donor instead of other donors such as glutathione (see Adenylyl-sulfate reductase (glutathione)). Structural studies As of late 2011, according to model version updates within the Protein Data Bank, only one structure has been solved for this class of enzymes, with the PDB accession code . The structure generally is tetrameric in nature with each monomeric composed of several helical β-sheet proteins with α-helical proteins in tow. The enzyme structure can be viewed on the PDB page. Active site The active site just as its glutaredoxin counterpart, contains a single cysteine based protein where the thioredoxin binds during electron donation. This including most other adenylyl-sulfate reductases The active site cleft is formed in the center of the enzyme's structure and is notably deep allowing for larger internal surface area for thioredoxin or other substrate binding, on any given protein subunit of the tetramer. The substrate binds onto the C-terminal side of the β-chains within the clef mediated by cysteines. There area few other parts of the synaptic cleft formed between certain loops, such as the "P loop" and the "LDTG motif", noted in some literature