Characterization of cytochrome oxidase purified from rat liver.

The purpose of this study was to characterize the physical properties of cytochrome c oxidase from rat liver. The enzyme was extracted from isolated mitochondria with nonionic detergents and further purified by ion-exchange chromatography on DEAE Bio-Gel A. The purified enzyme contained 9.64 nmol heme a/mg protein and one iron atom plus one copper atom for each heme a. The specific activity of the final preparation was 146 micromol of ferrocytochrome c oxidized/min x mg protein, measured at pH 5.7. The spectral properties of the enzyme were characteristic of purified cytochrome oxidase and indicated that the preparation was free of cytochromes b, c, and c1. In analytical ultracentrifugation studies, the enzyme sedimented as a single component with anS20,w of 5.35S. The Stokes radius of the enzyme was determined by gel filtration chromatography and was equal to 75 A. The molecular weight of the oxidase calculated from its sedimentation coefficient and Stokes' radius was 180,000, indicating that the active enzyme contained two heme a groups. The purified cytochrome oxidase was also subjected to dodecyl sulfate-polyacrylamide gel electrophoresis in order to determine its components. The enzyme was resolved into five polypeptides with the molecular weights of I, 27,100; II, 15,000; III, 11,900; IV 9800; and V, 9000.