CATALYTIC EFFECTS OF GLUTATHIONE-PEROXIDASE MIMETICS ON THE THIOL REDUCTION OF CYTOCHROME-C

The reduction of ferric cytochrome c by various thiols was studied. It was found that L-cysteine, L-cysteine methyl ester and D-penicillamin e were very efficient reductants for cytochrome c, whereas N-acetylate d aminoacids (N-acetyl-L-cysteine and N-acetyl-D-cysteine) reacted con siderably slower. A series of glutathione peroxidase mimetics and rela ted compounds were studied as catalysts for the N-acetyl-L-cysteine re duction of ferric cytochrome c. Diphenyl diselenide, t-butylthio pheny l selenide, S-(phenylseleno)-glutathione, N-(phenylseleno)-phthalimide and alpha-(phenylselenenyl)-acetophenone were all efficient reduction catalysts. Diphenyl disulfide, Ebselen and several derivatives thereo f were less potent catalysts whereas diaryl selenides and diphenyltell uride did not affect the rate of reduction when present in catalytic a mounts. The catalysis of diphenyl diselenide, selenosulfides, alpha-(p henylselenenyl)acetophenone, N-(phenylseleno)-phthalimide and Ebselen and derived compounds was suggested to involve the formation of arenes elenolate ions as redox-active species capable of transferring one ele ctron to the ferric cytochrome c. The resulting selenium centered aryl seleno radicals would then dimerize to regenerate the catalyst in the diselenide form. In the presence of diaryl ditellurides and N-acetyl-L -cysteine, ferric cytochrome c was also rapidly reduced. This reaction was stoichiometric with respect to the ditelluride reagent.