Kinetics of phosphatidylglycerol synthesis in isolated membrane vesicles from Escherichia coli containing different amounts of membrane-bound phosphatidic acid.

Abstract

Cytoplasmic membrane vesicles of Escherichia coli containing various amounts of phosphatidic acid ranging from 0.2% to more than 50% (mol/mol) of the total lipid has been prepared by de novo synthesis of phosphatidic acid in the isolated membranes from acyl-CoA esters and sn-glycerol 3-phosphate. The kinetics of CTP-initiated phosphatidylglycerol synthesis in the phosphatidic-acid-enriched membranes has been studied. Phosphatidic acid pools with high and low reactivity as substrate for phosphatidylglycerol synthesis were present in the membranes. The two pools were found identical with respect to fatty acid composition and content of molecular species. The rate of phosphatidylglycerol synthesis from the highly reactive phosphatidic acid pool was independent of the phosphatidic acid concentration in membranes containing from 0.2-30% (mol/mol) phosphatidic acid. Ca2+-ions were found to inhibit the synthesis of phosphatidylglycerol. On the basis of the findings presented it is suggested that phosphatidic acid probably plays a minor role as a feed-back modulator of sn-glycerol 3-phosphate acylation in E. coli, and that phosphatidylglycerol synthesis can occur at near maximal rate in growing cells.