Acyl‐Donor Specificities of Partially Purified 1‐Acylglycerophosphate Acyltransferase, 2‐Acylglycerophosphate Acyltransferase and 1‐Acylglycerophosphorylcholine Acyltransferase from Rat‐Liver Microsomes

1. A partially purified preparation containing 1‐acylglycerophosphate acyltransferase, 2‐acylglycerophosphate acyltransferase and 1‐acylglycerophosphorylcholine acyltransferase was obtained from rat liver microsomes which were resolved with a nonionic detergent, Triton X‐100, in glycine buffer pH 8.6. The purification procedure involves molecular sieve chromatography and sucrose density gradient centrifugation. 2. The partially purified 1‐acylglycerophosphate acyltransferase exhibits a significant specificity for mono‐ and dienoic fatty acyl‐CoA thioesters. The effectiveness of the various acyl‐donors examined is as follows: oleyl‐CoA > linoleyl‐CoA ∼ palmitoleyl‐CoA > palmityl‐CoA ∼ myristyl‐CoA; arachidonyl‐CoA, stearyl‐CoA and lauryl‐CoA are almost ineffective. The newly formed ester bond is sensitive to the action of phospholipase A2. 3. The partially purified 2‐acylglycerophosphate acyltransferase shows a predominant selectivity for saturated acyl‐CoA thioesters. Stearyl‐CoA is the most effective acyl‐donor, and palmityl‐CoA is utilized fairly efficiently. 4. The partially purified 1‐acylglycerophosphorylcholine acyltransferase is specific for arachidonyl‐CoA. 5. These findings, together with our previous studies on the acyl‐donor specificity of glycerophosphate acyltransferase, indicate that the asymmetric fatty acid distribution found in naturally occurring glycerolipids results mostly from the specific at the step of phosphatidic acid synthesis and partly from the deacylation‐reacylation cycle operating after the synthesis de novo of phospholipids.