Identification of an endogenous electron donor for biohydrogenation as alpha-tocopherolquinol

Four fluorescent compounds present in solvent extracts of Butyrivibrio fibrisolvens could serve as electron donors for the biohydrogenation of cis-9,trans-11-octadecadienoate in the presence of dithionite, which was itself inactive. One of the compounds was identified as alpha-tocopherolquinol and another as alpha-tocopherolquinone. A partially purified soluble enzyme preparation from B. fibrisolvens catalyzed the reduction of alpha-tocopherolquinone to alpha-tocopherolquinol in the presence of NADH with a stoichiometry of 1:1. The ratio of alpha-tocopherolquinone produced to fatty acid reduced was 2:1 when the tocopherol derivatives were extracted aerobically. When the extraction was carried out anaerobically, the ratio was 1. It is suggested that the oxidation of 2 molecules of alpha-tocopherolquinol, each to the semiquinone, provides the electrons required for the reduction of the cis-bond of the conjugated dienoic fatty acid. Although alpha-tocopherol, phylloquinol, and reduced menadione are inactive, ubiquinol-4, ubiquinol-10, and trimethylhydroquinone show about one-half the activity of alpha-tocopherolquinol. Plastoquinol and trimethylphytylbenzoquinol are as active as alpha-tocopherolquinol.