Biosynthesis of phosphatidic acid, lysophosphatidic acid, diglyceride, and triglyceride by fatty acyltransferase pathways in Escherichia coli.

Fatty acyl coenzyme A-glycerol 3-phosphate, fatty acyl coenzyme A-lysophosphatidic acid, fatty acyl coenzyme A-monoglyceride, and fatty acyl coenzyme A-diglyceride acyltransferase activities were found in a particulate fraction of broken cell preparations of Escherichiu coli. The synthesis of phosphatidic acid and lysophosphatidic acid catalyzed by these enzymes was demonstrated to be dependent upon the presence of glycerol 3-phosphate, fatty acyl-CoA, and magnesium ion. Magnesium ion was partially replaceable by calcium ion. Isolated, radiochemically pure lysophosphatidic acid served as a substrate in the synthesis of phosphatidic acid in an enzymatic reaction with fatty acyl-CoA. This observation suggests that lysophosphatidic acid functions as an intermediary in the synthesis of phosphatidic acid from glycerol j-phosphate and fatty acyl-CoA. Under similar conditions of incubation both monoglyceride and diglyceride functioned as acceptors of the fatty acyl moiety from fatty acyl-CoA. Glycerol, however, did not serve as a substrate in the acylation reaction. Glycerol was incorporated into phospholipid only when adenosine triphosphate was added to an incubation system capable of acylating glycerol d-phosphate. Lauryl, myristyl, pahnityl, stearyl, oleyl, linoleyl, linolenyl, cis-vaccenyl, and trans-vaccenyl coenzyme A derivatives were tested and found to be active substrates in vitro in the acylation of glycerol 3-phosphate. However, lauric, stearic, linoleic, linolenic, and trans-vaccenic acids have not been reported to exist as constituents of the phospholipids of E. coli. This finding suggests that the acyl transferase reaction does not possess the specificity required for excluding certain fatty acids which do not naturally occur in the phospholipids of E. coli.