Biosynthesis of lecithin in brain. Participation of cytidine diphosphate choline and phosphatidic acid

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Abstract
In dispersions of rat brain the incorporation of radioactivity from [C14]phosphorylchollne into the phosphatide fraction was increased by the addition of cytidine tri- phosphate to the incubation medium, but not by the addition of coenzyme A. Examination of the hydrolysis products of the labelled phosphatides showed that the radioactivity was confined to the lecithin fraction. In similar dispersions the incorporation of radioactivity from cytidine diphosphate [Cl4]-choline into the phosphatide fraction was increased by the addition of enzymically prepared diglycerides from naturally occurring lecithins, by the addition of synthetic D-[alpha] [beta]-diolein, but not by the addition of L-[alpha] [beta]-diolein. Again the radioactivity was confined to the lecithin fraction. The incorporation of radioactivity from DL-[alpha]-[Cl4]giycerophosphate into the phosphatide fraction was increased by the addition of coenzyme A, but not by the addition of cytidine tri-phosphate. Radioactivity from L-[alpha]-[C14]glycerophosphate was recovered in phosphatidic acid phosphatidylinositol and lecithin. The incorporation of radioactivity into lecithin was stimulated by the addition of non-labelled cytidine diphosphate choline. Phosphatidic acids were dephosphorylated to yield inorganic phosphate in preparations from rat brain. The dephosphorylation was inhibited by the presence of Mg2+ ions in the reaction medium. Phosphatidic acids incubated in Mg free medium stimulated the subsequent incorporation of radioactivity from cytidine diphosphate [C14]choline into lecithin. The addition of non-labelled cytidine diphosphate choline stimulated the incorporation of biologically prepared [C14]phosphatidic acid into lecithin. The results are discussed in relation to the biosynthesis of lecithin in brain.