The inhibition of mitochondrial peroxidation by ubiquinone and ubiquinol.

Ubiquinol-6 (reduced coenzyme Q6) was more effective than ubiquinone-6 and almost as effective as a-tocopherol in reducing the stable free radical diphenyl-p-picrylhydrazyl. The antioxidant activity of ubiquinol-6 was measured at low oxygen concentrations with an oxygen electrode. Ubiquinol-6 was found to be as e5cient as a-tocopherol as an inhibitor of the heme-catalyzed peroxidation of arachidonic acid emulsions. Ubiquinold was oxidized to ubiquinone-6 by free radical products of the heme-catalyzed decomposition of cumene hydroperoxide. a+Tocopherol did not inhibit this reaction. Light was used to catalyze the peroxidation of mitochondrial lipids at low concentrations of oxygen. This peroxidation was inhibited by the addition of ubiquinol-6 or cY-tocopherol to the mitochondria. Light-induced mitochondrial peroxidation was inhibited by ubiquinol-6 produced from exogenous ubiquinone-6 by the electron transport-linked oxidation of /3-hydroxybutyrate. Ubiquinols may function as antioxidants in the mitochondrion. This could explain why ubiquinones and related compounds have been found effective in the relief of certain vitamin E deficiency syndromes in some species.