Components of the mitochondrial inner membrane. 5. Interaction of detergents with cytochrome c oxidase

Abstract

The binding of ionic and nonionic, nondenaturing detergents to cytochrome c oxidase [beef heart] was examined. All detergents bind and displace part but not all of the phospholipid that is associated with the enzyme after isolation. From 6-10 phospholipid molecules, depending on the detergent used, do not exchange and these are mostly diphosphatidylglycerol molecules as 1st shown by Awasthi et al. The binding of Triton X-100 and deoxycholate to the cytochrome c oxidase complex was studied in detail. Both bind to the enzyme above their critical micelle concentrations: Triton X-100 in the amount of 180 .+-. 10 molecules/complex and deoxycholate in the amount of 80 .+-. 4 molecules/complex. In nonionic detergents, cytochrome c oxidase exists as a dimer (4 heme complex). The enzyme is dissociated into the monomer or heme aa3 complex by delipidation in bile salts. Cytochrome c oxidase probably requires a flexible, hydrophobic environment for maximal activity; the dimer or 4 heme complex may be the active species.