Components of the mitochondrial inner membrane. 3. Characterization of a seventh different subunit of beef heart cytochrome c oxidase. Similarities between the beef heart enzyme and that from other species

Abstract

Beef heart cytochrome c oxidase [EC 1.9.3.1] was resolved into 7 subunits by electrophoresis in highly cross-linked gels containing urea and sodium dodecyl sulfate. The MW of the polypeptides are estimated to be I:35,400; II:24,100; III:21,000; IV:16,800; V:12,400; VI:8200; and VII:4400. Subunits II and III can coelectrophorese on standard sodium dodecyl sulfate-polyacrylamide gels and appear as a single component with an apparent MW of 22,500. This accounts for previous reports that the beef heart enzyme contains only 6 subunits. Amino acid analysis of the isolated subunits I, II and III revealed that they have polarities of 35.5, 44.7 and 39.9%, respectively. All 3 subunits have an extremely high leucine content and a low percentage of basic amino acids relative to subunits IV-VII. The size, number and properties of subunits in the beef heart cytochrome c oxidase complex suggest that it has essentially the same subunit structure as the complexes isolated from Saccharomyces cerevisiae and Neurospora crassa.