Pathways for the synthesis of glycerophosphatides in Escherichia coli.

Presently available evidence indicates that phosphatidic acid is an essential intermediate in the biosynthesis of glycerophosphatides in Escherichia coli. Two alternative pathways for the synthesis of phosphatidic acid in E. coli have been proposed, one involving the acylation of L-glycerol j-phosphate, and the second the direct phosphorylation of o, /3-diglyceride, catalyzed by the enzyme diglyceride lrinase. If the latter pathway occurs to a significant extent in living cells of E. coli, one would expect to find a metabolically active pool of diglyceride in this organism. Pulse experiments with radioactive glycerol have failed to reveal the presence of such a pool, under conditions in which a very rapid synthesis of phosphatidic acid is taking place. Cellfree extracts of such cells, however, have been found to contain diglyceride kinase. Diglyceride lrinase has been shown to be highly stereospecific, catalyzing the phosphorylation of diglycerides with the formation of derivatives of Lglycerol 3-phosphate only. Some implications of these fmdings for the physiological function of diglyceride kinase are discussed.