ROLE OF TOCOPHEROLS IN THE BIOMEMBRANE LI PID-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 oth er and with the oxidation substrate) are discussed. Unlike the majorit y of synthetic phenol antioxidants, tocopherols exhibit a number of pr operties, such as: high affinity to peroxy radicals (the rate constant s 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 phenoxy l radicals formed and activity in the reaction of oxidation-chain tran sfer). The activity of tocopherol radicals in the chain transfer react ions depends on their structure and manifests itself in a marked depen dence of the inhibition extent on the oxidation conditions and the ant ioxidant concentration, up to the inverse effect. This can be used to control the oxidation rate: the radicals formed from tocopherols may s erve as a buffer maintaining the oxidation rate at a certain level in systems with different antioxidant concentrations (concentration contr ol) and with substrates of various unsaturation extent (substrate cont rol). Tocopherols exhibit a unique set of properties that allow them t o control the rate of lipid peroxidation and the physicochemical prope rties of biological membranes. It is this dual effect that provides th e feedback relations and;thereby maintains homeostasis in organism.