title: The effect of pH and ionic strength on the steady-state activity of isolated cytochrome C oxidase.
abstract: 1. The turnover number and apparent Km of isolated beef-heart cytochrome c oxidase were found to increase continuously when the pH was lowered from 8.6 to 4.6 (turnover number 32-630 s-1). In this pH range neither irreversible denaturation of the enzyme nor an optimum for the turnover number was observed. 2. The turnover number of cytochrome c oxidase was found to be independent of ionic strength. It was concluded that the dependence of the activity of cytochrome c oxidase on ionic strength is caused by a change in the value of Km for cytochrome c. 3. The pH dependence of the turnover number of cytochrome c oxidase can be described by a simple model in which at least three sites on the complex of cytochrome c oxidase with cytochrome c (pKa 8.0, 6.5 and 4.8) can take up a proton.
mesh_terms: D003574:Cytochrome c Group / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D010084:Oxidation-Reduction
chemical_list: D003574:Cytochrome c Group; D003576:Electron Transport Complex IV