UBIQUINONE-DEPENDENT RECYCLING OF VITAMIN-E RADICALS BY SUPEROXIDE

Superoxide-driven reduction of alpha-tocopheroxyl radical in the prese nce of ubiquinone-10 has been demonstrated in dimethylsulfoxide. Our H PLC measurements showed that ubiquinone-10 protected alpha-tocopherol against oxidation by KO2 in a concentration-dependent manner. alpha-To copherol was oxidized by KO2 to form ESR-detectable radicals of tocoph erol ubisemiquinone, In the presence of ubiquinone-10, neither these r adicals nor alpha-tocopheroxyl radicals (generated by uv light or PbOB 2) could be detected in ESR spectra. Instead, ESR signals of ubisemiqu inone-10 radicals were observed, Formation of ubisemiquinone-10 radica ls from ubiquinone-10 upon addition of KO2 was ascertained by their ch aracteristic ESR and uv-vis spectra, alpha-Tocopherol caused a concent ration-dependent decrease of the ubisemiquinone-10 radical steady-stat e concentration, We conclude that one electron reduction of ubiquinone -10 by superoxide ion resulting in the formation of ubiquinone-10 radi cals caused redox-cycling of alpha-tocopherol from its phenoxyl radica l, thus preventing loss of alpha-tocopherol, This suggests that coenzy me Q may have another physiological function, i.e., protection of alph a-tocopherol against superoxide-driven oxidation. (C) 1995 Academic Pr ess, Inc.