The purpose of the present investigation was to obtain an insight into the chemical properties of the active site of the enzyme rhodanese (thiosulfate: cyanide sulfurtransferase). This enzyme is widely distributed in nature, from bacteria to man. Several functions, including cyanide detoxification and synthe sis of iron-sulfur centers, have been proposed for this enzyme. Different disul fides with different chemical properties were allowed to react with the sulfhy dryl group in the active site of rhodanese. The Ellman reagent; 5,5'-dithiobis (2-nitrobenzoic acid), DTNB, reacted very slowly. A marked increase in the rate of reaction of rhodanese with DTNB was observed when cationic disulfides, cystamine and cystine, were present. No change was seen with non cationic disulfides dimethyl disulfide, 2-hydroxy ethyl disulfide, dithioglycolic acid oxidized glutathione, 2,2'-salicylic acid, 2,2'dipyridyl disulfide (2-PDS) and 4,4-dipyridyl disulfide (4-PDS). A Km of 2.0 and 2.5 mmol/1 was obtained for cystamine and cystine, respectively, while the Km for thiosulfate, the common substrate of the enzyme was 3.0 mmol/1. These results possibly indicate the existence of anionic groups in or in the vicinity of the active site which facilitate binding of the cationic disulfides. Furthermore, these data might suggest that these disulfides are the true physiological substrates of rhodanese.
کلید واژگان :rhodanes, activesite, disulfide reagents
ارزش ریالی : 600000 ریال
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