The enzyme is part of a system for detoxifying arsenate. The substrate binds to a catalytic cysteine residue, forming a covalent thiolate---As(V) intermediate. A tertiary intermediate is then formed between the arsenic, the enzyme's cysteine, and a glutathione cysteine. This intermediate is reduced by glutaredoxin, which forms a dithiol with the glutathione, leading to the dissociation of arsenite. Thus reduction of As(V) is mediated by three cysteine residues: one in ArsC, one in glutathione, and one in glutaredoxin. Although the arsenite formed is more toxic than arsenate, it can be extruded from some bacteria by EC 7.3.2.7, arsenite-transporting ATPase; in other organisms, arsenite can be methylated by EC 2.1.1.137, arsenite methyltransferase, in a pathway that produces non-toxic organoarsenical compounds. cf. EC 1.20.4.4, arsenate reductase (thioredoxin).
first reaction step is a nucleophilic displacement reaction by C10 on dianionic arsenate. Second step is a preferential nucleophilic attack of C82 on the monoanionic C10-arsenate intermediate stabilized by S17. Thiolate form of C82 is stabilized by an eight-residue alpha helix flanked by C82 and C89 and a hydrogen bond with T11. during the final step, C89 is activated as a nucleophile by structural alterations of the redox helix
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SYSTEMATIC NAME
IUBMB Comments
arsenate:glutathione/glutaredoxin oxidoreductase
The enzyme is part of a system for detoxifying arsenate. The substrate binds to a catalytic cysteine residue, forming a covalent thiolate---As(V) intermediate. A tertiary intermediate is then formed between the arsenic, the enzyme's cysteine, and a glutathione cysteine. This intermediate is reduced by glutaredoxin, which forms a dithiol with the glutathione, leading to the dissociation of arsenite. Thus reduction of As(V) is mediated by three cysteine residues: one in ArsC, one in glutathione, and one in glutaredoxin. Although the arsenite formed is more toxic than arsenate, it can be extruded from some bacteria by EC 7.3.2.7, arsenite-transporting ATPase; in other organisms, arsenite can be methylated by EC 2.1.1.137, arsenite methyltransferase, in a pathway that produces non-toxic organoarsenical compounds. cf. EC 1.20.4.4, arsenate reductase (thioredoxin).