The oxidation of alpha-tocopherol and trolox by peroxynitrite.
Peroxynitrite reacts rapidly with alpha-tocopherol to generate a mixture of species. The predominant products are 8a-methoxytocopherone in methanol and alpha-tocopherylquinone in acetonitrile. Only a small fraction (about 2% of original alpha-tocopherol) was detected as alpha-tocopheroxyl radical in either solvent. We propose that peroxynitrite oxidizes alpha-tocopherol in a two-electron process yielding the alpha-tocopherone cation. The two-electron oxidation may be either concerted or sequential. The fate of the alpha-tocopherone cation is solvent dependent. In acetonitrile it undergoes hydrolysis, in the presence of trace amounts of water, to form alpha-tocopherylquinone. In methanol it undergoes nucleophilic addition to yield 8a-methoxytocopherone. Our data suggest that two-electron oxidation of alpha-tocopherol by peroxynitrite represents the major pathway, whereas one-electron oxidation to generate alpha-tocopheroxyl radical is a minor pathway. The biological consequences of two-electron oxidation of alpha-tocopherol are discussed.
Hogg
N
N
Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226.
Joseph
J
J
Kalyanaraman
B
B
D000097:Acetonitriles; D002839:Chromans / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006868:Hydrolysis; D000432:Methanol; D009566:Nitrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D012997:Solvents; D014810:Vitamin E / Q000737:chemistry*
D000097:Acetonitriles; D002839:Chromans; D005609:Free Radicals; D009566:Nitrates; D012997:Solvents; D014810:Vitamin E; C039642:peroxynitric acid; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D000432:Methanol; C032159:acetonitrile