Enzymatic synthesis of a novel acetylated neutral lipid (related to platelet activating factor, PAF) by acyl-CoA: 1-alkyl-2-acetyl-sn-glycerol acyltransferase

Recent data from our laboratory have described the complete enzymatic steps for the de novo synthesis of alkylacetylglycerols and their subsequent conversion to PAF. Experiments are reported here to show that the alkylacetylglycerols also are a substrate for an acyltransferase. Homogenates of HL-60 cells produced labeled 1-alkyl-2-acetyl-3-acyl-sn-glycerols from 1-[3H]hexadecyl-2-acetyl-sn-glycerol, 1-alkyl-2-[3H]acetyl-sn-glycerol, or [1-14C]linoleic acid when incubated with CoA (0.1 mM), ATP (10 mM), and Mg2+ (95 mM). Formation of labeled alkylacetylacyl-glycerols by the acyltransferase required CoA, ATP, and Mg2+. The labeled alkylacetylacylglycerol produced had an identical Rf to that of an authenic standard; after treatment with pancreatic lipase, the sn-3 acyl moiety was hydrolyzed to regenerate the original 1-alkyl-2-acetyl-sn-glycerol precursor. [1-14C]Linoleic acid was an excellent substrate for the acylation step, whereas [1-14C]oleic acid was barely utilized. Kinetic properties and related characteristics of this enzyme that forms the acetyl analog of a triglyceride will be presented. Although the function of this new type of acetylated neutral lipid class is presently unknown, it could serve as a potential precursor reservoir in the de novo route of PAF synthesis