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

The subunit structure of ubiquinone-cytochrome c reductase (complex III) has been examined and eight different polypeptides have been identified. Apparent molecular weights for each have been obtained by one or more methods including polyacrylamide gel electrophoresis in sodium doecyl 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, 4 800-9 00. Individual polypeptides have been purified and the amino acid composition of several of these have been determined. At least one polypeptide, the apoprotein of cytochrome b, is hydrophobic in character and this is a mitochondrially synthesized component (B. Lorenz, W. Kleinow, and H. Weiss (1974), Hoppe-Seyler's Z. Physiol. Chem. 355, 300). Other polypeptides including the hemoprotein of cytochrome c1 are more hydrophilic in amino acid composition.