High de novo synthesis of glycerolipids compared to deacylation-reacylation in rat liver microsomes.

A microsomal system characterized by high flux through the entire de novo pathway from glycerol phosphate to phosphatidylcholine and triacylglycerol has been developed. Optimum synthesis of phosphatidylcholine requires CDPcholine, Mg2+, KCl and a palmitoyl-CoA-generating system containing palmitic acid, ATP and CoA. Incorporation of [14C]glycerol phosphate into phosphatidylcholine/triacylglycerol synthesis ratio decreases as palmitate is increased. Phosphatidylcholine synthesis from glycerol phosphate is stimulated more by palmitate than by other saturated fatty acids; phosphatidylcholine synthesis increases with increasing unsaturation of the added fatty acids. The ratio of incorporation of [3H]palmitate to [14C]glycerol phosphate was determined for phosphatidic acid, diacylglycerol, phosphatidylcholine and triacylglycerol. This ratio is approximately 2 for all diacylglycerolipids and 3 for triacylglycerol. In our system, incorporation of palmitate into microsomal glycerolipid proceeds primarily by the de novo pathway, with minimal fatty acid recycling via deacylation-reacylation.