Lipid–protein and lipid–lipid interactions in cytochrome oxidase model membranes

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Abstract
Two lipid environments are detected in membranous cytochrome oxidase, using spin labeling techniques. This model membrane system consists of closed vesicular membranes formed spontaneously when the membrane protein is isolated with its accompanying phospholipids. The data show both an immobilized component, which is constant in amount, and a fluid component. Based on spectral analysis, the interpretation is that the bound component represents a single layer of lipid immobilized on the surface of the protein between the hydrophobic protein complex and the adjacent fluid bilayer regions. Maximal enzyme activity of this functional protein complex is attained when all of the bound sites are occupied, and above this level additional phospholipid (bilayer) has little or no effect on the enzyme activity.