GPX3, also known as glutathione peroxidase 3, belongs to the glutathione peroxidase family, which functions in the detoxification of hydrogen peroxide. GPX3 protects cells and enzymes from oxidative damage, by catalyzing the reduction of hydrogen peroxide, lipid peroxides and organic hydroperoxide, by glutathione. This protein is one of only a few proteins known in higher vertebrates to contain selenocysteine, which occurs at the active site of glutathione peroxidase and is coded by the nonsense (stop) codon TGA.