Components of the mitochondrial inner membrane. 2. The polypeptide composition of ubiquinone-cytochrome c reductase (complex III) from beef heart mitochondria

Abstract

The subunit structure of ubiquinone-cytochrome c reductase (complex III) was examined and 8 different polypeptides were identified. Apparent molecular weights for each were obtained by one or more methods, including polyacrylamide gel electrophoresis in sodium dodecyl sulfate and in sodium dodecyl sulfate-8 M urea and by gel filtration in sodium dodecyl sulfate and in 6 M guanidine hydrochloride. Values obtained are as follows: I, 47,500; II, 45,500; III, 29,500; IV, 27,800; V, 24,800; VI, 13,900; VII, 10,700; VIII, 4800-9000. Individual polypeptides were purified and the amino acid composition of several of these were determined. At least 1 polypeptide, the apoprotein of cytochrome b, is hydrophobic in character and this is a mitochondrially synthesized component. Other polypeptides including the hemoprotein of cytochrome c1 are more hydrophilic in amino acid composition.