Catalytic mechanism of Sulfiredoxin from Saccharomyces cerevisiae passes through an oxidized disulfide sulfiredoxin intermediate that is reduced by thioredoxin.

Sulfiredoxin catalyzes the ATP-dependent reduction of overoxidized eukaryotic 2-Cys peroxiredoxin PrxSO(2) into sulfenic PrxSOH. Recent mechanistic studies on sulfiredoxins have validated a catalytic mechanism that includes formation of a phosphoryl intermediate on the sulfinyl moiety of PrxSO(2), followed by an attack of the catalytic cysteine of sulfiredoxin on the phosphoryl intermediate that leads to formation of a thiosulfinate intermediate PrxSO-S-sulfiredoxin. Formation of this intermediate implies the recycling of sulfiredoxin into the reduced form. In this study, we have investigated how the reductase activity of the Saccharomyces cerevisiae sulfiredoxin is regenerated. The results show that an oxidized sulfiredoxin under disulfide state is formed between the catalytic Cys(84) and Cys(48). This oxidized sulfiredoxin species is shown to be catalytically competent along the sulfiredoxin-recycling process and is reduced selectively by thioredoxin. The lack of Cys(48) in the mammalian sulfiredoxins and the low efficiency of reduction of the thiosulfinate intermediate by thioredoxin suggest a recycling mechanism in mammals different from that of sulfiredoxin from Saccharomyces cerevisiae.