Biochemical function of selenium and its relation to vitamin E

Glutathione peroxidase (glutathione:H2O2 oxidoreductase, E.C. 1.11.1.9), isolated from ovine and bovine erythrocytes, has recently been shown to contain 4 selenium atoms per mole, an average of 1 Se per protein subunit of about 22,000 molecular weight. Selenium deficiency in the rat, chick and sheep causes dramatic decreases in the activity of this enzyme in the tissues, but certain sites such as liver are affected more than others. Decreases in glutathione peroxidase correlate with lesions caused by selenium deficiency and appear useful in diagnosing selenium deficiency. Glutathione peroxidase is an important enzyme in destroying H2O2 and organic hydroperoxides such as lipid hydroperoxides. It therefore guards against oxidative damage to the cell membranes and other oxidant-sensitive sites in the cell. While this selenium-dependent system destroys lipid hydroperoxides and other peroxides, vitamin E is believed to protect against oxidant damage to membranes by preventing the formation of lipid hydroperoxides. A scheme is proposed, based on oxidant damage and its prevention, which accounts for the interaction between selenium, vitamin E, unsaturated lipids, sulfur-containing amino acids, and cell damaging agents such as oxidant stressors and toxicants such as silver and tri-o-cresyl phosphate. The background for such a scheme is reviewed.