Purification and fine structure of reduced coenzyme Q-cytochrome C reductase in the mitochondrial membrane

For the purpose of revealing the molecular organization of the mitochondrial membrane the authors attempted to clarify the fine structure of reduced coenzyme Q-cytochrome c reductase and also studied how the CoQH2-cyt. c reductase is arranged in the mitochondrial membrane by systematic analyses of fractions from the purification process of CoQH2-cyt. c reductase. 1. Purified CoQH2-cyt. c reductase contained high concentration of cyt. b (9.5 mμmoles per mg protein) and cyt. Cl (4.5 mμmoles per mg protein), and was almost free from cyt. c, a, flavoproteins, primary dehydrogenases and ATPase. The enzyme complex also showed a high specific activity (48 μmoles of cyt. c reduced per mg protein per min at 30°). 2. CoQH2-cyt. c reductase was composed of particles of about 120 Å in diameter with irregular form, some time exhibiting electron opaque cores. In the loose aggregates of the particles, the size of each particle was about 95 Å in diameter. 3. An intimate correlation was observed between the particles of CoQH2cyt. c reductase and those on the surface of the NADH-cyt. c reductase fraction. 4. Regular arrays of uniform particles (about 82 Å in diameter with a center to center distance of about 100 Å) were observed on the surface of the submitochondrial membrane (brown membrane) obtained from beef heart mitochondria by treatment with deoxycholate (0.1 mg / mg protein) and KCl (72 g/l). The correlation between these particles and CoQH2-cyt. c reductase was discussed.