The protein encoded by this gene belongs to the glutathione peroxidase family, members of which catalyze the reduction of hydrogen peroxide, organic hydroperoxides and lipid hydroperoxides, and thereby protect cells against oxidative damage. Several isozymes of this gene family exist in vertebrates, which vary in cellular location and substrate specificity. Expression of this gene has been observed in embryos and olfactory epithelium; however, the exact function of this gene is not known. This isozyme is a selenoprotein in humans, containing the rare amino acid selenocysteine (Sec) at its active site. Sec is encoded by the UGA codon, which normally signals translation termination. The 3' UTRs of selenoprotein mRNAs contain a conserved stem-loop structure, designated the Sec insertion sequence (SECIS) element, that is necessary for the recognition of UGA as a Sec codon, rather than as a stop signal. The orthologs of this gene in mouse and rat (and some other species) contain a cysteine (Cys) residue in place of the Sec residue, and their corresponding mRNAs lack the SECIS elements. [provided by RefSeq, Oct 2016].