LIPID SYNTHESIS IN RAT LIVER PARTICLES: DIVERSION OF SYNTHESIS FROM TRIGLYCERIDE TO LECITHIN BY THE IN VITRO ADDITION OF CYTIDINE DIPHOSPHATE CHOLINE

Abstract

When particle preparations from rat or chicken liver were incubated in a suitable medium containing α-glycerophosphate-C¹⁴, radioactivity was recovered from lecithin, phosphatidyl inositol, phosphatidic acid, and triglyceride. Whole homogenate and various particle preparations catalyzed the dephosphorylation of a number of phosphatidic acids, with the liberation of inorganic P.It is currently believed that liver preparations are capable of catalyzing the esterification of L-α-glycerophosphate, with the formation of L-α-phosphatidic acid, which subsequently may be dephosphorylated to form D-α,β-diglyceride. The diglyceride so formed may then give rise either to lecithin, by combining with phosphorylcholine from cytidine diphosphate choline, or to triglyceride, by combining with fatty acid from fatty acyl coenzyme A. If these reactions occur in liver particle preparations, it should be possible, by the addition in vitro of unlabelled cytidine diphosphate choline, to divert the synthesis of lipid from the formation of triglyceride to the formation of lecithin. In experiments designed to put this hypothesis to the experimental test, such a diversion of lipid synthesis was achieved.