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Biosynthesis of molecular species of CDP‐diglyceride from endogenously‐labeled phosphatidate in rat liver microsomes

1976; Wiley; Volume: 11; Issue: 4 Linguagem: Inglês

10.1007/bf02544050

1558-9307

Bruce J. Holub, J. Piekarski,

Biochemical Acid Research Studies

Abstract The biosynthesis of [ 14 C] CDP‐diglyceride was studied using rat liver microsomes which were endogenously labeled with [ 14 C] phosphatidic acid by preincubation of unlabeled microsomes with sn ‐[ 14 C]glycerol‐3‐phosphate and appropriate cofactors. The formation of CDP‐diglyceride from radioactive phosphatidate showed an absolute requirement for CTP and MgC1 2 . The newly formed [ 14 C] CDP‐diglyceride was characterized by thin layer chromatography (TLC), isotopic labeling from radioactive CTP, and its ability to serve as substrate for the microsomal enzyme, CDP‐diglyceride: inositol phosphatidyltransferase. The distributions of radioactive glycerol‐3‐phosphate among the various chemical classes of microsomal [ 14 C] phosphatidate and [ 14 C]CDP‐diglyceride were determined following argentation TLC of their 1,2‐diglyceride acetate derivatives. Most of the radioactivity among the phosphatidic acids was present in the monoenoic (36%) and dienoic (33%) molecular species, whereas 10, 8, 4, and 8% were associated with the saturates, trienes, tetraenes, and polyenes, respectively. Similar distributions of radioactivity were found among the corresponding classes of newly formed CDP‐diglyceride. Only a slight enrichment of radioactivity in the tetraenoic CDP‐diglyceride was found relative to the corresponding phosphatidates. Therefore, under the conditions of study, the microsomal CTP:phosphatidate cytidylyltransferase produces mainly monoenoic and dienoic species of CDP‐diglyceride and shows little specificity towards different molecular species of phosphatidic acids. The present results suggest also that the arachidonoyl phosphatidate derived from the microsomal acylation of sn ‐glycerol‐3‐phosphate is not likely the major source of arachidonic acid in liver phosphatidylinositol.