FIG. 3.

Catalytic activity of the peroxiredoxins. The peroxidatic cysteine of peroxiredoxins reacts with hydrogen peroxide to form a sulfenic acid. The fate of this species varies depending on the class of peroxiredoxin, with the typical 2-Cys proteins forming an intermolecular disulfide, the atypical 1-Cys (A) proteins forming intramolecular disulfides (B), and the 1-Cys sulfenic acid directly reduced by other factors (C). The hyperoxidation reaction is only shown for the typical 2-Cys peroxiredoxins, but could occur with peroxiredoxin 5 and 6, though little is known about the susceptibility of these proteins to hyperoxidation.