Incorporation of large quantities of phospholipid by net de novo synthesis in cytoplasmic membrane vesicles of Escherichia coli.

De novo phospholipid synthesis has been studied in cytoplasmic membrane vesicles of Escherichia coli in the presence of sn-glycerol 3-phosphate, CTP, serine and acyl-CoA. Continuous addition of acyl-CoA was found to result in phospholipid biosynthesis during more than 4 h of incubation and phospholipid corresponding to 3--4-times the total amount of lipid originally present was synthesized under these conditions. The major biosynthetic products were phosphatidylglycerol, cardiolipin and phosphatidic acid. The composition of the accumulated lipid could to some extent be varied by adding the acyl-CoA to the vesicles at different rates. The newly synthesized lipid was found to be present in a population of membrane vesicles (80% of the total) which had a decreased density in comparison to the starting material. Electron microscopy of negatively stained preparations before and after incubation indicated that the vesicular nature of the cytoplasmic membrane fragments was preserved throughout incubation. A minor population of vesicles, the density of which was unchanged during incubation, contained little de novo synthesized lipid. The activity of the sn-glycerol-3-phosphate acyltransferase decreased during incubations to 25% in vesicles which had accumulated phospholipid. Conversion of phosphatidic acid into phosphatidylglycerol and cardiolipin was uneffected by the lipid content of the vesicles.