title: Selective reactivity of rhodanese sulfhydryl groups with 5,5'-dithio-bis(2-nitrobenzoic acid).
abstract: The reactivity of the sulfhydryl groups of sulfur-containing and sulfur-free rhodanese (thiosulfate : cyanide sulfurtransferase, EC 2.8.1.1) with 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB) has been investigated. Only 0.6 sulfhydryl group of the sulfur-containing enzyme reacts with DTNB. After removal of sulfur from persulfide groups a further 0.6 sulfhydryl group (i.e. a total of 1.2) becomes accessible to the reagent. The resulting enzyme-thionitrobenzoate complex shows an absorption spectrum with a shoulder at 325 nm due to bound thionitrobenzoate. Both thiosulfate and cyanide remove thionitrobenzoate from the enzyme restoring its catalytic properties. The modified enzyme is protected from alkylation by iodoacetate until thionitrobenzoate is removed. The existence of a further sulfhydryl group close to the catalytic one is suggested.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002417:Cattle; D003486:Cyanides / Q000378:metabolism; D003545:Cysteine; D004228:Dithionitrobenzoic Acid; D007461:Iodoacetates; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013053:Spectrophotometry; D013329:Structure-Activity Relationship; D013466:Sulfurtransferases / Q000378:metabolism; D013884:Thiosulfate Sulfurtransferase / Q000378:metabolism; D013885:Thiosulfates / Q000378:metabolism
chemical_list: D003486:Cyanides; D007461:Iodoacetates; D013885:Thiosulfates; D004228:Dithionitrobenzoic Acid; D013466:Sulfurtransferases; D013884:Thiosulfate Sulfurtransferase; D003545:Cysteine