Diphosphatidylglycerol is required for optimal activity of beef heart cytochrome c oxidase.

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Abstract
Isolated beef heart cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1) contains 4 or 5 molecules of tightly bound diphosphatidylglycerol per monomer (2-heme complex). This lipid could be removed in part or wholly by mixing the enzyme with high concentrations of Triton X-100 and then centrifuging the mixture through a glycerol gradient equilibrated in the same detergent. Cytochrome c oxidase retaining 3 or more diphosphatidylglycerol molecules per monomer was fully active when assayed in 1-oleoyl lysophosphatidylcholine. Upon removal of one or more of these diphosphatidylglycerols, enzymic activity was lost. Full activation could be obtained by adding diphosphatidylglycerol to the assay mixture along with lysophosphatidylcholine but not by adding phosphatidylcholine or phosphatidylethanolamine. Direct binding experiments, kinetic studies and previous work using arylazidocytochrome c derivatives indicate that diphosphatidylglycerol is involved in binding of substrate cytochrome c to cytochrome c oxidase.