ELECTRON TRANSPORT-LINKED UBIQUINONE-DEPENDENT RECYCLING OF ALPHA-TOCOPHEROL INHIBITS AUTOOXIDATION OF MITOCHONDRIAL-MEMBRANES

The objective of this study was to elucidate the antioxidative roles o f coenzyme Q (CoQ) and alpha-tocopherol in mitochondrial membranes by determining whether CoQ directly scavenges peroxyl-and alkoxyl-radical s or indirectly regenerates cu-tocopherol during autooxidation of mito chondrial membranes. A comparison of the interaction between alpha-toc opherol and CoQ during autooxidation was made between bovine and rat h eart mitochondria, which differ similar to 15-fold in their alpha-toco pherol content. Autooxidation of both bovine and rat heart mitochondri a resulted in the formation of thiobarbituric-acid-reactive substances and protein carbonyls; however, the differences in the autooxidizabil ity of mitochondria between rat and bovine heart mitochondrial membran es were relatively minor. Supplementation of rat heart mitochondria wi th succinate caused reduction of CoQ to ubiquinol while cu-tocopherol concentration remained unaffected during autooxidation. In contrast, i n the absence of succinate, CoQ was present in the oxidized form (ubiq uinone) and the mitochondrial membranes were depleted of cy-tocopherol , CoQ concentrations remained unchanged over time irrespective of the presence or absence of succinate, In the absence of succinate, autooxi dation of bovine SMPs, supplemented with different amounts of alpha-to copherol, was inversely related to the amount of alpha-tocopherol, whe reas in the presence of succinate autooxidation was greatly reduced. R esults of this study indicate that during autooxidation of mitochondri a, alpha tocopheroI acts as the direct radical scavenger, whereas ubiq uinol regenerates cu-tocopherol. (C) 1998 Academic Press.