The effect of cytochrome c oxidase on lipid polymorphism of model membranes containing cardiolipin

The effect of cytochrome c oxidase incorporation on the lipid polymorphism of the cardiolipin-Ca2+ system was investigated by 31P NMR and freeze-fracture electron microscopy. The integral membrane protein has a stabilizing effect on the bilayer organization of cardiolipin, in that it inhibits the Ca2+-induced HII phase formation of this lipid for Ca2+/cardiolipin molar ratios of 1-10. At a Ca2+/cardiolipin molar ratio of 25, about 80% of the lipid is organized in the HII phase and a structural phase separation occurs between the cardiolipin-Ca2+ complex organized in the hexagonal HII phase without protein and bilayer structures with incorporated protein.