Effect of phospholipids on the catalytic subunits of the mitochondrial F0.F1-ATPase.

Beef heart mitochondrial F0.F1-ATPase was reconstituted into phospholipid liposomes using the octylglucoside solubilization, discontinuous sucrose gradient centrifugation procedure described in the preceding manuscript (Laird, D., Smith Eble, K., and Cunningham, C. (1986) J. Biol. Chem. 261, 14844-14850). The influence of individual phospholipids (phosphatidylcholine (PC), phosphatidylethanolamine (PE), and diphosphatidylglycerol (DPG)) on the kinetic parameters related to ATPase activity were investigated. The specific activities for the PC, PE, and DPG reconstituted preparations were 9.8, 6.8, and 7.6 mumol of ATP hydrolyzed per min/mg of protein, respectively. The F0.F1-DPG complex demonstrated a 40% decrease in the Km for ATP. Both the F0.F1-PC and the F0.F1-PE complexes exhibited Ki values for adenyl-5'-yl imidodiphosphate and guanyl-5'-yl imidodiphosphate approximately 2.5 times lower than those obtained in the absence of exogenous phospholipid. The F0.F1-DPG complex displayed Ki values 11.7- and 1.8-fold lower for adenyl-5'-yl imidodiphosphate and guanyl-5'-yl imidodiphosphate, respectively, as compared to the lipid-depleted enzyme. The phospholipids with which F0.F1 were reconstituted also influenced the ATP-induced decrease in the fluorescence of enzyme-associated aurovertin. The rate of the ATP-elicited decrease in aurovertin fluorescence was accelerated in the presence of all three phospholipids with DPG having the most dramatic effect; the t1/2 for maximal decrease in aurovertin fluorescence was 4.3 s for lipid-deficient enzyme and 0.48 s with the F0.F1-DPG complex. The effects of phospholipids on these parameters associated with the catalytic center of the ATPase suggest that phospholipids can modulate catalytic events occurring in F1. In the intact mitochondrion the primary role of phospholipids may be to stabilize conformations of the enzyme consistent with its range of activities.