Role of tocopherols in the biomembrane lipid peroxidation

The rate constants of elementary reactions of the oxidation inhibition by tocopherols of different structurs (peroxy radical destruction by antioxidant molecules, interaction of inhibitor radicals with each other and with the oxidation substrate) are discussed. Unlike the majority of synthetic phenol antioxidants, tocopherols exhibit a number of properties, such as: high affinity to peroxy radicals (the rate constants for their reactions with these radicals are by one or two orders of magnitude greater than the rate constants for reactions involving most of synthetic phenols; they possess a fairly high stability of phenoxyl radicals formed and activity in the reaction of oxidation-chain transfer). The activity of tocopherol radicals in the chain transfer reactions depends on their structure and manifests itself in a marked dependence of the inhibition extent on the oxidation conditions and the antioxidant concentration, up to the inverse effect. This can be used to control the oxidation rate: the radicals formed from tocopherols may serve as a buffer maintaining the oxidation rate at a certain level in systems with different antioxidant concentrations (concentration control) and with substrates of various unsaturation extent (substrate control). Tocopherols exhibit a unique set of properties that allow them to control the rate of lipid peroxidation and the physicochemical properties of biological membranes. It is this dual effect that provides the feedback relations and;thereby maintains homeostasis in organism.