The Role of Quinones in the Mitochondrial Electron Transport System

that have been considered as possible electron carriers in the mitochoridrial electron transport system, only coenzyme Q (CoQ) has been unambiguously shown to function in this capacity and this report will be concerned primarily with the role of CoQ in mitochondria. Prior to the discovery of CoQ, reports by Nason and his . 2 suggested that cm-tocoph-erol might function as an electron carrier in the mitochondrial electron transport system. The following is a brief summary of our current views on the role of tocopherol in the mito-chondrial electron transport system. Hatefi and his associates in our laboratory have examined the tocopherol content of beef heart mitochondria and of submitochondrial particles and some of their data is given in Table I. In agreement with the earlier reports from the laboratories of Nason2 and of Slater,3 substantial quantities of cm-tocopherol are present in mitochondria and its distribution would suggest that it is closely associated with the reduced diphosphopyridine nucleotide (DPNH) oxidase system. In contrast to total lipid and CoQ, the level of a-tocopherol is almost twice as high in the purified DPNH cytochrome C reductase preparation as in the original mitochondria and it is evident that concentration of tocopherol parallels concen-tration of DPNH cytochrome c reductase activity. Whether this has any physiologic significance or is merely a reflection of th