Mitochondrial membrane components. 8. Polypeptides in the succinate-coenzyme Q reductase segment of the respiratory chain

Abstract

Beef heart mitochondria complex II (succinate-coenzyme Q reductase) was resolved into 10 different polypeptides by polyacrylamide gel electrophoresis. Four polypeptides, CII-1, CII-2, CII-3 and CII-4 with MW of 70,000, 24,000, 13,500 and 7000, were present in large amounts in all preparations examined. CII-1 and CII-2 are the flavoprotein and Fe-S protein, respectively, of succinate dehydrogenase; CII-3 and CII-4 were not functionally identified. Six polypeptides were present in much smaller amounts as judged by staining intensity, and each of these comigrated with components in complex III. Amino acid compositions of several of the minor components in complex II were identical with that of an equivalently migrating polypeptide in complex III. Succinate-coenzyme Q reductase apparently contains 4 different polypeptides and is contaminated with variable amounts of complex III when isolated as complex II.