Abstract
The acyl‐acceptor specificities of the 1‐acylglycerolphosphate acyltransferase and 1‐acyl‐glycerophosphorylcholine acyltransferase resolved from rat liver microsomes have been investigated with various synthetic 1‐acyl‐sn‐glycerol 3‐phosphate and 1‐acyl‐sn‐glycero‐3‐phosphorylcholine derivatives differing in their fatty acid constituent (myristic, palmitic, stearic, oleic, linoleic or arachidonic acid) as well as with various 1‐acyl‐sn‐glycerophospholipid analogues carrying different polar head groups (phosphorylcholine, phosphoryldimethylethanolamine, phosphorylmonomethyl‐ethanolamine, phosphorylethanolamine, phosphorylethanol or phosphate). The activities of the two acyltransferases are virtually not affected by the fatty acid constituent of the respective acyl acceptors, except that the 1‐stearoyl and 1‐arachidonoyl derivatives are somewhat less effective acyl acceptors for both enzymes. The 1‐acylglycerophosphorylcholine acyltransferase utilizes several acyl acceptors differing in the polar head group with the following order of effectiveness: 1‐acyl‐sn‐glycero‐3‐phosphoryl‐choline > 1‐acyl‐sn‐glycero‐3‐phosphoryldimethylethanolamine > 1‐acyl‐sn‐glycero‐3‐phosphoryl‐monomethylethanolamine ∼ 1‐ acyl‐sn‐glycero‐3‐phosphorylethanolamine. 1 ‐Acyl‐sn‐glycero‐3‐phosphorylethanol and 1‐acyl‐sn‐glycerol 3‐phosphate are ineffective. In contrast, the 1‐acylglycerolphosphate acyltransferase is highly specific for 1‐acyl‐sn‐glycerol 3‐phosphate. The fatty acid constituent of the acylacceptors exerts essentially no effect on the acyl‐donor specificity of each enzyme except in the case of 1‐arachidonoyl‐sn‐glycero‐3‐phosphorylcholine. Furthermore, the acyl‐donor specificity of the 1‐acylglycerophosphorylcholine acyltransferase is virtually not affected by the polar head group of the acyl acceptor. The results obtained in this work and in our previous investigations support the view that the substrate specificities of glycerolphosphate acyltransferase, 1‐acylglycerolphosphate acyltransferase and 1‐acylglycerophosphorylcholine acyltransferase make an essential contribution to the nonrandom fatty acid distribution in naturally occurring glycerolipids.
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