Diacylglycerol-phosphatidylethanolamine exchange in Escherichia coli

The conversion of [3H]- or [14C]diacylglycerol to labelled phosphatidylethanolamine by dialysed, particulate fraction of Escherichia coli was studied. The reaction occurred in the presence of hydroxylamine, under which conditions, the synthesis of [14C]phosphatidylethanolamine from CDP-diacylglycerol and [14C]serine did not occur. The conversion was enhanced by addition of dilauroyl- or dioleoylphosphatidylethanolamine. A conversion of [3H]- or [14C]phosphatidylethanolamine to labelled diacylglycerol could also be readily demonstrated provided unlabelled diacylglycerol was added. Double-labelled [acyl-3H, 32P]phosphatidylethanolamine was converted to labelled diacylglycerol without formation of labelled water-soluble products. The formation of double-labelled phosphatidylethanolamine from [3H]diacyl[14C]glycerol or of double-labelled diacylglycerol from [acyl-3H,glycerol-14C]phosphatidylethanolamine occurred without significant change in isotope ratio. When [acyl-3H]phosphatidylethanolamine was incubated with increasing concentrations of [acyl-14C]diacylglycerol, correspondingly increasing concentrations of [14C]phosphatidylethanolamine were formed which matched the concentrations of [3H]diacylglycerol produced concurrently. It was concluded that E. coli extracts can catalyze an exchange between the diacylglycerol moiety of phosphatidylethanolamine and free diacylglycerol with complete sparing of the phosphoethanolamine moiety.