UBIQUINONE-DEPENDENT RECYCLING OF VITAMIN-E RADICALS BY SUPEROXIDE

Superoxide-driven reduction of alpha-tocopheroxyl radical in the presence of ubiquinone-10 has been demonstrated in dimethylsulfoxide. Our HPLC measurements showed that ubiquinone-10 protected alpha-tocopherol against oxidation by KO2 in a concentration-dependent manner. alpha-Tocopherol was oxidized by KO2 to form ESR-detectable radicals of tocopherol ubisemiquinone, In the presence of ubiquinone-10, neither these radicals nor alpha-tocopheroxyl radicals (generated by uv light or PbOB2) could be detected in ESR spectra. Instead, ESR signals of ubisemiquinone-10 radicals were observed, Formation of ubisemiquinone-10 radicals from ubiquinone-10 upon addition of KO2 was ascertained by their characteristic ESR and uv-vis spectra, alpha-Tocopherol caused a concentration-dependent decrease of the ubisemiquinone-10 radical steady-state concentration, We conclude that one electron reduction of ubiquinone-10 by superoxide ion resulting in the formation of ubiquinone-10 radicals caused redox-cycling of alpha-tocopherol from its phenoxyl radical, thus preventing loss of alpha-tocopherol, This suggests that coenzyme Q may have another physiological function, i.e., protection of alpha-tocopherol against superoxide-driven oxidation. (C) 1995 Academic Press, Inc.