Electron Transport-Linked Ubiquinone-Dependent Recycling of α-Tocopherol Inhibits Autooxidation of Mitochondrial Membranes

The objective of this study was to elucidate the antioxidative roles of coenzyme Q (CoQ) and α-tocopherol in mitochondrial membranes by determining whether CoQ directly scavenges peroxyl- and alkoxyl-radicals or indirectly regenerates α-tocopherol during autooxidation of mitochondrial membranes. A comparison of the interaction between α-tocopherol and CoQ during autooxidation was made between bovine and rat heart mitochondria, which differ ∼15-fold in their α-tocopherol content. Autooxidation of both bovine and rat heart mitochondria resulted in the formation of thiobarbituric-acid-reactive substances and protein carbonyls; however, the differences in the autooxidizability of mitochondria between rat and bovine heart mitochondrial membranes were relatively minor. Supplementation of rat heart mitochondria with succinate caused reduction of CoQ to ubiquinol while α-tocopherol concentration remained unaffected during autooxidation. In contrast, in the absence of succinate, CoQ was present in the oxidized form (ubiquinone) and the mitochondrial membranes were depleted of α-tocopherol. CoQ concentrations remained unchanged over time irrespective of the presence or absence of succinate. In the absence of succinate, autooxidation of bovine SMPs, supplemented with different amounts of α-tocopherol, was inversely related to the amount of α-tocopherol, whereas in the presence of succinate autooxidation was greatly reduced. Results of this study indicate that during autooxidation of mitochondria, α-tocopherol acts as the direct radical scavenger, whereas ubiquinol regenerates α-tocopherol.