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. a hydroperoxide + 2 glutathione = an alcohol + glutathione disulfide + H2O Optimum pH is 7.8. Homotetramer; interconnecting Prx and Grx domains of different monomers. 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 the hybrid peroxiredoxin hyPrx5, no C(R) is present and C(P) instead is reduced directly by the redox-active site in the Grx-domain of another monomer, regenerating peroxidase activity of the enzyme. The oxidized glutaredoxin is reduced by reduced glutathione (GSH) (Probable). C(P) may also be reactivated by glutathionylation and subsequent reduction by the Grx-domain (Probable). In the N-terminal section; belongs to the peroxiredoxin family. Prx5 subfamily. In the C-terminal section; belongs to the glutaredoxin family.