Lipid-protein interactions in membranes: interaction of phospholipids with respiratory enzymes of Escherichia coli membrane.

Membranes were isolated from Escherichia coli and treated with cold 90% aqueous acetone to remove neutral lipids and phospholipids. This treatment resulted in the loss of more than 90% of o-lactate, NADH, and succinate oxidase activities. The activities could be restored to the lipid-depleted particles by preincubation, for 3 min at 37”, with a dispersion of coenzyme Q,,, and an appropriate phospholipid. The three oxidase activities exhibited differences in their response to the structure of the polar portion of the phospholipid. Cardiolipin was the only phospholipid component which could activate o-lactate oxidase. The activity of NADH oxidase could be restored by preincubation of the acetone-treated particles with dispersions of phosphatidylglycerol, phosphatidylserine, or cardiolipin, although to different extents; lecithin or phosphatidylethanolamine was ineffective. The most active phospholipid component for succinate oxidase was cardiolipin, followed by phosphatidylserine, phosphatidylethanolamine, phosphatidylglycerol, and lecithin. The effect of lipids on the kinetic parameters of the enzymatic activities was also investigated. The apparent K,,, values for the activities of reconstituted particles were significantly altered by various lipids. These experiments give evidence for a specificity towards the structure of the polar group of phospholipids in the segment of the electron transport chain of Escherichia coli from the dehydrogenase through coenzyme Q. They also indicate that differences between the interaction of various proteins with phospholipids exist. In addition, they give evidence for a possible role of lipids in the regulation of enzymatic activities.