Glutathione (GSH) peroxidase family; tetrameric selenoenzymes that catalyze the reduction of a variety of hydroperoxides including lipid peroxidases, using GSH as a specific electron donor substrate. GSH peroxidase contains one selenocysteine residue per subunit, which is involved in catalysis. Different isoenzymes are known in mammals,which are involved in protection against reactive oxygen species, redox regulation of many metabolic processes, peroxinitrite scavenging, and modulation of inflammatory processes.
Comment:Selenocysteine forms part of the active triad. Upon reduction of hydroperoxides, the selenolate anion is oxidized to selenenic acid which is then regenerated by glutathione for another catalytic cycle. Because of its lower redox potential, selenocysteine is a better reductant than cysteine under physiological conditions.