Interactions between ubiquinones and vitamins in membranes and cells.

The interaction between ubiquinones and vitamin E was studied in the inner membranes of rat liver mitochondria, liposomes and human erythrocyte plasma membranes. Free radicals were produced by addition of exogenous oxidants, and their reaction with chromanols and ubiquinone was followed by ESR and HPLC. Membranes were made deficient in ubiquinone but sufficient in alpha-tocopherol and were reconstituted with added ubiquinone. With these membrane preparations it was shown that (i) in the inner mitochondrial membranes there is a requirements for ubiquinone in the enzymatic recycling of vitamin E; (ii) succinate-ubiquinone reductase incorporated in liposomes cannot protect vitamin E in the absence of ubiquinone and (iii) in human erythrocyte plasma membranes protection against the loss of vitamin E can be provided by NADH-cytochrome-b5-dependent enzymatic recycling. We conclude that ubiquinonols (ubisemiquinones) reduce vitamin E through electron transport.