Metabolism of Glycerolipids

In the course of W-tracer studies on the biological synthesis of lecithin in lung tissue slices, the ratio of fatty acid activity to glycerol activity in lecithin was higher than in the triglyceride fraction. It was suggested that the observed isotope distributions could be due to turnover of the fatty acid portion of lecithin without a corresponding synthesis and breakdown of the remainder of the molecule (1). Such a turnover of fatty acid might require the combined actions of a phospholipase, an enzyme activity found in many tissues (2-4), and also a lysophosphatide-acylating enzyme which has not been demonstrated before. Further studies of lecithin metabolism showed that the product of phospholipase action, lysolecithin, could be utilized for lecithin synthesis by rat liver microsomes. This result is in contrast to that obtained in the chemical acylation of lysolecithin, which has been unsuccessful with several different acyl derivatives (5, 6), although Tattrie and McArthur (7) recently obtained a 31% yield of lecithin by allowing an acid chloride to react with lysolecithin in anhydrous chloroform for 3 days. It is the purpose of this paper to describe the properties of the microsomal system which catalyzes the acylation of lysolecithin to form lecithin. This reaction requires ATP and CoA, and involves the formation of an acyl-CoA derivative.