Thiol-specific peroxidase that catalyzes the reduction of hydrogen peroxide and organic hydroperoxides to water and alcohols, respectively. Plays a role in cell protection against oxidative stress by detoxifying peroxides (By similarity). May be involved in intracellular redox signaling (Probable). [glutaredoxin]-dithiol + a hydroperoxide = [glutaredoxin]-disulfide + an alcohol + H2O Monomer. The active site is a conserved redox-active cysteine residue, the peroxidatic cysteine (C(P)), which makes the nucleophilic attack on the peroxide substrate. The peroxide oxidizes the C(P)-SH to cysteine sulfenic acid (C(P)-SOH), which then reacts with another cysteine residue, the resolving cysteine (C(R)), to form a disulfide bridge. The disulfide is subsequently reduced by an appropriate electron donor to complete the catalytic cycle. In this 1-Cys peroxiredoxin, no C(R) is present and C(P) instead forms a disulfide with a cysteine from another protein or with a small thiol molecule. C(P) is reactivated by glutathionylation and subsequent reduction by glutaredoxin (Grx), or by thioredoxin (Trx). Belongs to the peroxiredoxin family. Prx5 subfamily.