Abstract
Action of vitamin E as a chain-breaking antioxidant has been studied and summarized from kinetic and mechanistic points of view. The rate and mechanism of scavenging of lipid peroxyl radicals were studied in homogeneous solution by measuring oxygen uptake, products formation, chemiluminescence and free radicals with electron spin resonance. The oxidation of phospholipid liposomal membranes and its inhibition by tocopherols were studied aiming at elucidating the action of tocopherols in the membranes. It was found that tocopherols suppress the oxidation of phosphatidylcholine liposomes by scavenging both aqueous radicals attacking from outside of the membranes and lipophilic radicals within the membranes. It was suggested that laterally tocopherols move fairly rapidly but that it gets less efficient for tocopherols to scavenge radicals as they go deeper into the interior of the membrane. The phytyl side chain had a profound effect in the retainment of tocopherols in the membranes but it makes tocopherols difficult to move between the membranes. 2, 2, 5, 7, 8-Pentamethyl-6-chromanol could penetrate and transfer between the liposomal membranes freely. Tocopherols also suppressed the oxidative hemolysis of erythrocytes induced by free radicals. It was found that tocopherol within the erythrocyte membranes was the most effective in suppressing hemolysis induced by aqueous radicals by scavenging chain-carrying radicals and breaking the chain propagation.
