The role of vitamin E in biological membranes.

The view that vitamin E functions in living systems primarily as a lipid antioxidant and free-radical scavenger has gained widespread acceptance. As a result of a large recent increase in knowledge of the potentially damaging effects of certain oxygen metabolites, the role of vitamin E can now be placed in context as one factor in a complex protective system that includes superoxide dismutase, catalase, and peroxidases, including the seleno-enzyme glutathione peroxidase. alpha-Tocopherol is presumed to occur in association with intracellular membranes, but the techniques on which this presumption was based have been insufficiently sensitive to allow its confident acceptance. The hypothesis that the unique molecular structure of the phytyl side-chain of alpha-tocopherol enables specific physicochemical interactions with arachidonyl residues of membrane phospholipids can explain how molecules of alpha-tocopherol are bound within biological membranes. The interaction between alpha-tocopherol and unsaturated phospholipids has been studied using a tissue culture technique. The results suggest that alpha-tocopherol is capable of exerting a controlling influence upon the linoleyl and arachidonyl residues within membrane phospholipids which cannot be explained on the basis of the antioxidant function of the vitamin, and which may provide evidence for the above hypothesis.