title: Electron transfer in monomeric forms of beef and shark heart cytochrome c oxidase.
abstract: Beef heart cytochrome c oxidase is dimeric in reconstituted membranes and in nonionic detergents at physiological pH [Henderson, R., Capaldi, R. A., & Leigh, J. (1977) J. Mol. Biol. 112, 631; Robinson, N.C., & Capaldi, R. A. (1977) Biochemistry 16, 375], raising the possibility that this aggregation state is a prerequisite for enzymatic activity. A procedure for dissociating the enzyme into monomers is presented. This involves treating the protein with high concentrations of Triton X-100 at pH 8.5. The electron transfer activity of the monomer is comparable to that of the dimer under identical assay conditions. The beef heart cytochrome c oxidase monomer was found to be heterogeneous in hydrodynamic studies, probably due to dissociation of associated polypeptides, including subunit III. Monomer molecular weights in the range 129 000-160 000 were obtained. Previous studies have indicated that shark heart cytochrome c oxidase is monomeric under physiological conditions. Sedimentation equilibrium studies reported here confirm this. The elasmobranch enzyme, with a similar polypeptide composition to that of beef enzyme, was determined to have a molecular weight of 158 000.
mesh_terms: D000818:Animals; D001704:Biopolymers; D002417:Cattle; D002845:Chromatography / Q000379:methods; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008970:Molecular Weight; D009206:Myocardium / Q000378:metabolism*; D012754:Sharks; D013045:Species Specificity
chemical_list: D001704:Biopolymers; D003576:Electron Transport Complex IV