Regulation of fatty acid composition of cytidine diphosphate diacylglycerol by acyl transfer reactions.

Cytidine diphosphate monoacylglycerol was prepared by the action of snake venom phospholipase on cytidine diphosphate diacylglycerol and shown to be readily acylated by rat liver microsomes. Acylation was monitored by spectrophotometric assay or by measuring the incorporation of radioactivity from ‘%-labeled acyl-CoA esters. The product was identified as CDP-diacylglycerol. The acylation reaction was time-dependent, showed a linear response to microsomal protein concentration and had a pH optimum of 7.0. Under optimal conditions of acylation positional distribution studies by pancreatic lipase treatment of the diacylglycerol moiety released enzymatically from CDP-diacylglycerol confirmed that radioactive unsaturated thioesters were incorporated mainly into position 2. However, with oleoyl-CoA as acyl group donor and with low concentrations of lysolipid acceptor incorporation was largely into position 1, indicating that both positional isomers of the lysolipid had been produced. Acylation rates with unsaturated thioesters were superior to those obtained with saturated thioesters. With freshly prepared microsomes a selective preference was shown for arachidonoyl-CoA at low concentrations of lysolipid acceptor (20 and 40 PM). However, tit higher concentrations of CDP-monoacylglycerol less unsaturated thioesters were more effective than arachidonoyl-CoA, indicating that lysolipid acceptor concentration is one variable controlling fatty acid selectivity. The high rates of acylation of CDP-monoacylglycerol obtained in these experiments suggest that this is an important mechanism for regulating the fatty acid composition of the liponucleotide in rat liver.