Abstract
Cytochrome c oxidase has been reconstituted with two synthetic phospholipids, dioleoylphosphatidylcholine and dioleoylphosphatidylethanolamine. Vesicles prepared from either of these two lipids alone showed no stimulation of enzyme activity upon addition of carbonyl cyanide (trifluoromethoxy)phenylhydrazone and valinomycin, indicating that they were leaky to small ions. However, when mixtures of the two lipids were used for the reconstitution, tightly coupled vesicles could be obtained. The coupling ratio was dependent upon the ratio of dioleoylphosphatidylcholine to dioleoylphosphatidylethanolamine and also on the lipid-to-protein ratio. Maximal rates of enzyme activity were not significantly different with different lipid mixtures. The results are discussed in terms of both the size distribution of the reconstituted vesicles and the possible requirement for a variety of lipid species to ensure tight sealing at the lipid-protein interface.
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