Adenylyl-sulfate reductase (EC 1.8.99.2) is an enzyme that catalyzes the chemical reaction of the reduction of adenylyl-sulfate/adenosine-5′-phosphosulfate (APS) to sulfite through the use of an electron donor cofactor. The products of the reaction are AMP and sulfite, as well as an oxidized electron donor cofactor.
. . . Adenylyl-sulfate reductase . . .
This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with other acceptors. The systematic name of this enzyme class is AMP, sulfite:acceptor oxidoreductase (adenosine-5′-phosphosulfate-forming). Other names in common use include adenosine phosphosulfate reductase, adenosine 5′-phosphosulfate reductase, APS-reductase, APS reductase, AMP, sulfite:(acceptor) oxidoreductase, and (adenosine-5′-phosphosulfate-forming). This enzyme participates in selenium metabolism and sulfur metabolism.[1]
APS reductase catalyzes the reversible transformation of APS to sulfite and AMP, which is the rate determining step of the overall reaction.[2] The reaction catalyzed by APS reductase is as follows:
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Sulfate has to be activated to APS by ATP sulfurylase at the expense of one ATP, hence this reaction requires an input of energy.[2] The reaction above occurs in a strictly anaerobic environment.[2] The two electrons come from a reduced cofactor, in this case reduced FAD.[3] The forward direction requires one AMP molecule; however, research suggests that the reverse reaction requires two AMP molecules (one acting on the substrate and one inhibiting the forward reaction).[3] The reversible reaction occurs when AMP binds to the Arg317 residue, changing the confirmation of Arg317 and APS reductase as a whole, which provides the thermodynamic driving force to go in the reverse direction.[3]
APS reductases are involved in both assimilatory and dissimilatory sulfate reduction.[4] Dissimilatory sulfate reduction takes sulfate and transforms it into sulfide, a sulfur source that can be distributed throughout the body.[4] Assimilatory sulfate reduction takes sulfate and turns it into cysteine.[4] Dissimilatory and assimilatory pathways both use APS reductases as a metabolic tool to produce a sulfur source and amino acids, respectively.[4]
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