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 PbO2) 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.
D004121:Dimethyl Sulfoxide; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D008163:Luminescent Measurements; D010084:Oxidation-Reduction; D013057:Spectrum Analysis; D013481:Superoxides / Q000737:chemistry*; D014451:Ubiquinone / Q000737:chemistry*; D014810:Vitamin E / Q000737:chemistry*
D005609:Free Radicals; D013481:Superoxides; D014451:Ubiquinone; D014810:Vitamin E; D004121:Dimethyl Sulfoxide