Studies on the reconstitution of the structure and function of mitochondrial inner membrane. I. Structure and function of the membrane formed by the purified complex 3 and complex IV of the mitochondrial electron transfer chain

In order to elucidate the molecular organization of mitochondrial inner membrane, biochemical and electron microscope observations were made on the formation of membrane structure and function by the purified complexes of the electron transfer chain of beef heart mitochondria. Purified complex III (CoQ-cytochrome c reductase) and complex IV (cytochrome oxidase) were soluble in the presence of bile salts. They were, however, aggregated to form membrane by washing out the bile salts. When the membranous complexes III and IV were mixed, both membranes were separate by density gradient centrifugation and the vesicle which contained both complexes could not be formed and CoQH2-oxidase activity was hardly re;tored. When the mixture of the solubilized complexes III and IV were diluted to remove the bile salts, a membranous vesicle in which both complexes were assembled was formed. CoQH2-oxidase activity was restored in accordance with the formation of the membrane. The membrane which contained any desired propotion of each complexes could be obtained. These facts indicate that the complexes of the electron transfer chain conjugate two-dimentionally each other and form the membrane to carry electrons from substrate to oxygen most efficiently.