Studies on the Substrate Specificity of the Phospholipase A1 of the Plasma Membrane of Rat Liver

The phospholipase A1 from the plasma membranes of the rat liver catalyzes a transacylation between acylglycerols in addition to hydrolysis. Only the acyl group from position 1 can be donated; that in position 2 is not utilized. Compounds which contain either primary or secondary hydroxyls can be utilized as acyl acceptor molecules. The acceptor molecule may not be bulky, however, as shown by the lack of utilization of diglycerides, monoacylglycerophosphorylethanolamine and cholesterol. The addition of mono- and diacylglycerols with acyl chains of different length and unsaturation caused varying degrees of inhibition. Dialkylglycerols did not inhibit the enzyme as well as diacylglycerols which demonstrates that the nature of the bond on the glycerol affects the binding of the lipid to the enzyme. These results substantiate our earlier postulate that the enzyme has separate binding sites for acyl donor and acyl acceptor molecules.