The synthesis of phosphatidic acid from diglyceride and adenosine triphosphate in extracts of brain microsomes.

Previous studies in several laboratories have shown that phosphatidic acid becomes labeled with P3% in cell-free preparations of brain during oxidative phosphorylation (l-3). Kornberg and Pricer (4) found an enzyme in liver which catalyzes the synthesis of phosphatidic acid from a-glycerophosphate and coenzyme A thiol esters of fatty acids. McMurray et al. (2) found this pathway to be present in brain homogenates and in brain mitochondria. In the present study, this pathway was also found to be present in brain microsomal fractions. However, a different pathway for phosphatidic acid synthesis has also been found in brain microsomes and deoxycholate extracts of microsomes. In this reaction, diglyceride prepared from cabbage phosphatidic acid is phosphorylated by adenosine triphosphate. The enzyme which catalyzes the formation of phosphatidic acid via this pathway has been termed diglyceride kinase. Diglyceride prepared from brain lecithin is a poor substrate, and 1-palmityl,2-oleyl diglyceride is even poorer. The activity of the enzyme in brain microsomes is greatly increased by treatment of the microsomes with suitable concentrations of deosycholate. A phosphatase which liberates inorganic phosphate from cabbage phosphatidic acid is also present in the deoxycholate extracts of brain microsomes; the enzyme shows comparatively slight activity, if any, toward n-oJdistearoyl)phosphatidic acid. The combined action of the phosphatase and the diglyceride kinase in these extracts catalyzes the exchange of phosphate in cabbage phosphatidic acid.