Regulation by Lipids of Plant Microsomal Enzymes

Abstract

Cytidine-diphospho-choline diacyl-glycerol phosphorylcholine phosphotransferase activity wsas demonstrated in potato (S. tuberosum L.) microsomes and the incorporation of cytidine-diphospho[14C]choline into phosphatidylcholine was characterized by the time course of 14C incorporation and the effect of microsomal protein concentration on choline incorporation. Potato microsomes were progressively delipidated by treatments (2 min at 0.degree. C) with increasing amounts of phospholipase C from Bacillus cereus. A decrease in choline phosphotransferase activity occurred in parallel with the progressive hydrolysis of membrane phospholipids. A 70% (or more) phospholipid hydrolysis provoked the total inactivation of the enzyme. Adding back exogenous phospholipids (in the form of liposomes) to phospholipase C-treated membranes restored the enzymic activity. Restoration could be obtained with egg yolk phospholipids as well as with potato phospholipids. Restoration was time dependent and completed after 10 min.; restoration was dependent on the quantity of liposomes added to lipid-depleted membranes. The best restorations were obtained with 1-2.5 mg of phospholipid/mg of microsomal protein; higher phospholipid to protein ratios were less efficient or inhibitory. The phospholipid dependence of the cytidine-diphospho-choline phosphotransferase from potato microsomes is demonstrated.