Positional Specificity of <italic>sn</italic>-Glycerol 3-Phosphate Acylation during Phosphatidate Formation by Rat Liver Microsomes

Abstract

A microsomal preparation isolated from rat liver catalyzed the acylation of sn-glycerol 3-phosphate with both palmitoyl-CoA and oleoyl-CoA. The optimum pH was 7.5 for both acyl-CoA's, and the apparent Km values for glycerophosphate were 1.0 and 1.2 mM with palmitoyl-CoA and oleoyl-CoA as acyl donors, respectively. The major reaction product was diacyl-sn-glycerol 3-phosphate in the standard assay system with either acyl-CoA. Acyl-sn-glycerol 3-phosphate (monoacyl-GP) was added to the incubation system to trap newly synthesized radioactive intermediates. Radioactive monoacyl-GP was trapped effectively by the addition of nonlabeled 1-acyl-GP but ineffectively by adding nonlabeled 2-acyl-GP, regardless of whether palmitoyl-CoA or oleoyl-CoA was used as an acyl donor. The monoacyl-GP trapped in the presence of 1-acyl-GP was mostly the 1-acyl-GP isomer, regardless of which acyl-CoA was used. The system with added 2-acyl-GP produced various results as regards the isomeric monoacyl-GP accumulated. Although the pathway via the 2-acyl-GP could not be excluded completely in this experiment, diacyl-GP formation from glycerophosphate in rat liver microsomes appeared to occur primarily via the 1-acyl-GP as an intermediate, regardless of whether palmitoyl-CoA or oleoyl-CoA was used as an acyl donor.