SUCCINATE UBIQUINONE REDUCTASE LINKED RECYCLING OF ALPHA-TOCOPHEROL IN RECONSTITUTED SYSTEMS AND MITOCHONDRIA - REQUIREMENT FOR REDUCED UBIQUINONE

Studies have demonstrated that accumulation of mitochondrial tocopheroxyl radical, the primary oxidation product of α-tocopherol, accompanies rapid consumption of tocopherol. Enzyme-linked electron flow lowers both the steady-state concentration of the radical and the consumption of tocopherol. Reduction of tocopheroxyl radical by a mitochondrial electron carrier(s) seems a likely mechanism of tocopherol recycling. Succinate-ubiquinone reductase (complex II) was incorporated into liposomes in the presence of tocopherol and ubiquinone-10. After inducing formation of tocopheroxyl radical, it was possible to show that reduced ubiquinone prevents radical accumulation and tocopherol consumption. There was no evidence of direct reduction of tocopheroxyl radical by succinate-reduced complex II. These reactions were also measured using ubiquinone-1 and α-C-6-chromanol (2,5,7,8-tetramethyl-2-(4′-methylpentyl)-6-chromanol) which are less hydrophobic analogues of ubiquinone-10 and α-tocopherol. Mitochondrial membranes were made deficient in ubiquinone but sufficient in α-tocopherol and were reconstituted with added quinone. With these membranes it was shown that mitochondrial enzymelinked reduction of ubiquinone protects α-tocopherol from consumption, and there is a requirement for ubiquinone. This complements the observations made in liposomes and we propose that reduced mitochondrial ubiquinones have a role in α-tocopherol protection, presumably through efficient reduction of the tocopheroxyl radical. © 1992.