Behaviour of Beef-Heart Cytochrome c Oxidase in Reconstituted Proteovesicles. A Systematic Evaluation of the Influence of Phospholipid Polar Headgroup and Fatty-Acyl Side Chains

Abstract

1. Phospholipid-depleted cytochrome c oxidase is incorporated in vesicles, built up of phospholipids of known polar headgroup and fatty-acyl side chains. 2. Maximal reactivation is obtained only when the fatty-acyl side chains provide a fluid environment. 3. Fluid zwitterionic phospholipids are found to be more efficient reactivators than fluid anionic ones. 4. Irrespective of the polar headgroup type, two narrow ranges of activation energies for the enzymatic reaction are calculated from the Arrhenius plots: 81--92 kJ/mol in solid and 51--61 kJ/mol in fluid conditions. 5. Cytochrome c oxidase is also incorporated in a series of vesicles, each built up of an equimolar amount of two phospholipids which differ in their polar headgroup type and/or their fatty-acyl side chain characteristics. From the localization of the enzyme activity profiles, obtained with these mixtures, tentative deductions are made about the preference of cytochrome c oxidase for different phospholipid molecules.