title: Conjugation of dopa and 5-S-cysteinyldopa with cysteine mediated by superoxide radical.
abstract: cytotoxicity of catechols has been ascribed to their binding with proteins through sulfhydryl groups. Superoxide radical (O2-) generated in hypoxanthine-xanthine oxidase system at pH 7.4 mediated conjugation of dopa with cysteine to form cysteinyldopas. Similarly, 5-S-cysteinyldopa gave 2,5-S,S-dicysteinyldopa. The rates of oxidation of the catechols by O2- appear to be comparable to that of reduction of nitro-blue tetrazolium by O2-. These results suggest that catechols may exert cytotoxicity in cells where biochemical defence against O2- or the quinone oxidation products is not sufficient.
mesh_terms: D002374:Catalase / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism*; D003548:Cysteinyldopa / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism*; D005609:Free Radicals; D009580:Nitroblue Tetrazolium; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D005609:Free Radicals; D013481:Superoxides; D003548:Cysteinyldopa; D009580:Nitroblue Tetrazolium; D004295:Dihydroxyphenylalanine; D002374:Catalase; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D003545:Cysteine; D010100:Oxygen