Plasma membrane NADH-coenzyme Q0 reductase generates semiquinone radicals and recycles vitamin E homologue in a superoxide-dependent reaction

We investigated the ability of plasma membrane CoQ reductase (PMQR) purified from pig liver to reduce phenoxyl radicals of a vitamin E homologue, Trolox, We report that NADH-driven one-electron reduction of CoQ(0) catalyzed by PMQR produced CoQ(0) semiquinone radical and CoQ(0)H(2), These in turn, recycle vitamin E homologue, Trolox, via reducing its phenoxyl radical. A significant part of NADH/PMQR-catalyzed reduction of CoQ(0) (and Trolox recycling) was superoxide-dependent. Overall, our results demonstrate that PMQR in the model system used can act as an antioxidant enzyme that recycles water-soluble homologues of coenzyme Q and vitamin E. (C) 1998 Federation of European Biochemical Societies.