Stimulation of potato microsomal NADH-cytochrome c reductase by acidic phospholipids

Potato microsomal membranes were solubilized by 0.5% sodium cholate solutions. Separation of lipids from proteins was realized by two successive gel filtrations on two different Sephadex columns. Lipid-free microsomal proteins maintained a high NADH-ferricyanide reductase activity but had a lowered (20%) NADH-cytochrome c reductase activity. The latter activity was strongly stimulated when lipid-free proteins were integrated, by sonication, into phosphatidylserine or phosphatidylinositol liposomes. Some stimulation was obtained also with phosphatidylcholine-lysophosphatidylcholine (7:3) mixtures. Other phospholipids were far less active or even inhibitory. Acidic phospholipids stimulate NADH-cytochrome c reductase activity by increasing noticeably the apparent affinities of enzymatic proteins for NADH or cytochrome c.