Succinate-ubiquinone Reductase Activity Research Articles

Resolution and Reconstitution of the Mitochondrial Electron Transport System: I. Reconstitution of the Succinate-Ubiquinone Reductase

Abstract 1. Succinate dehydrogenase formed a complex with coupling factor 4 (F4) from beef heart mitochondria, either in the presence or in the absence of phospholipids. Succinate dehydrogenase bound to F4 remained insensitive to 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione and did not react with ubiquinone. 2. If cytochrome b was included in the complex, a succinate-ubiquinone reductase activity sensitive to 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione was reconstituted. Although required, cytochrome b did not appear to undergo oxidation-reduction. 3. The appearance of succinate-ubiquinone reductase was dependent on the use of reconstitutively active succinate dehydrogenase. Succinate dehydrogenase prepared in the absence of succinate was bound to the complex but was only active with N-methylphenazinium methyl sulfate as acceptor. 4. Phospholipids were essential for the succinate-ubiquinone reductase activity. Purified lecithin or phosphatidylethanolamine, but not cardiolipin, substituted for the crude phospholipid extract in the reconstitution of the complex. Complexes made with mitochondrial phospholipids had a higher specific activity and were more stable than those made with soybean phospholipids. Incubation of cytochrome b with soybean phospholipids resulted in complete loss of reconstitutive property of cytochrome b. 5. It is concluded that mitochondrial cytochrome b, in addition to its function in the electron transport, has a structural role in the organization of the members of the electron transport chain.