Abstract
A series of oxidants caused thiol oxidation in the monothiol yeast cytochrome c. However, only the weaker oxidants (cupric sulfate, o-iodosobenzoate, and potassium ferricyanide) caused disulfide (dimer) formation, but the stronger oxidants ( N-bromosuccinimide, iodine, H 2O 2, and a lipid peroxide) caused the formation of monomeric oxidation products exclusively. At high concentrations, ferricyanide and o-iodosobenzoate caused the formation of both monomeric and dimeric oxidation products. Acid pH also favored higher oxidation by o-iodosobenzoate. It is postulated that the oxidation mechanism involves two competitive reactions: a reaction producing disulfide dimers and a reaction producing a highly oxidized monomeric product, probably the sulfonic acid, and which requires a strong oxidant. The efficiency of thiol oxidation by peroxides in yeast cytochrome c, as in other hemoproteins, was much lower than in other proteins or small thiols. This is probably due to competition by the hematin residue for the oxidizing species produced by peroxides.
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