Positional Specificities of Acyl Coenzyme A:Glycerophosphate and Acyl Coenzyme A:Monoacylglycerophosphate Acyltransferases in Escherichia coli

A particulate preparation isolated from Escherichia coli B catalyzes the acylation of 1-acyl-sn-glycerol 3-phosphate (1-acyl-GP) with both oleoyl-CoA and palmitoyl-CoA. The optimum conditions were determined for the acyl-CoA: 1-acyl-GP acyltransferase. The acyltransferase is specific for the 1-acyl-GP and does not acylate 2-acyl-sn-glycerol 3-phosphate (2-acyl-GP) under the conditions used. The particulate preparation also catalyses the acylation of sn-glycerol 3-phosphate (glycerophosphate) with both palmitoyl-CoA and oleoyl-CoA. When palmitoyl-CoA is the substrate, both monoacyl-sn-glycerol 3-phosphate (monoacyl-GP) and diacyl-sn-glycerol 3-phosphate (diacyl-GP) are produced. The two products show a typical precursor-product relationship. When oleoyl-CoA is used, the major product is diacyl-GP; monoacyl-GP is formed, but the amount reaches a very low steady state level within 2 min of incubation. Structural analyses of the monoacyl-GP formed after short time incubations of glycerophosphate with unsaturated or saturated acyl-CoAs showed the major isomer to be 1-acyl-GP. The amounts of 2-acyl-GP formed are relatively small. The lack of accumulation of 2-acyl-GP during the acylation of glycerophosphate is not due to the isomerization of 2-acyl-GP to the 1-acyl-GP isomer. During the acylation of radioactive glycerophosphate with unsaturated acyl-CoA, radioactive monoacyl-GP is trapped effectively by the addition of nonlabeled 1-acyl-GP but ineffectively by adding nonlabeled 2-acyl-GP. The monoacyl-GP trapped in the presence of either 1-acyl-GP or 2-acyl-GP is mostly the 1-acyl-GP isomer. Thus, the pathway of diacyl-GP synthesis from glycerophosphate in E. coli is primarily via the 1-acyl-GP as intermediate regardless of whether the substrate is saturated or unsaturated acyl-CoA.