Vitamin E protects proteins against free radical damage in lipid environments

The fragmentation of the membrane protein monoamine oxidase in submitochondrial particles was induced by defined free radicals during radiolysis and by a system dependent on hydrogen peroxide and a transition metal. By injection of α-tocopherol in vivo, the levels of this physiological antioxidant in the mitochondrial preparations could be elevated more than ten-fold. In both radical-generating systems the presence of high levels of α-tocopherol in the membrane substantially retarded the protein fragmentation, in parallel with lipid peroxidation. It is suggested that membrane-bound proteins are damaged during lipid peroxidation and that α-tocopherol protects cells against both types of damage.