Transacylation between diacylphospholipids and 2-acyl lysophospholipids catalyzed by Escherichia coli extract

When 2-acyl lysophosphatidylethanolamine, 2-acyl lysophosphatidylglycerol, and 2-acyl lysophosphatidylcholine were incubated with the envelope fraction of Escherichia coli in the presence of Mg2+ ion, they were acylated to the corresponding diacylphospholipids. The inner and outer membrane fractions both had acylation activity. 2-Acyl lysophosphatidylethanolamine was shown to be acylated at the 1-position by an endogenous acyl donor present in the envelope fraction. Under the conditions used, acylation was specific for 2-acyl lysophosphatidylethanolamine, and the 1-acyl isomer was not appreciably acylated. The acylation was resistant to N-ethylmaleimide and p-chloromercuribenzoate, but was inhibited by Cu2+ and Hg2+ ions. Ca2+ and Mg2+ ions stimulated the activity about 1.5-fold, but EDTA was not inhibitory. The activity had a broad pH optimum between 6 and 8. On boiling the envelope fraction, about 55% of the activity was lost rapidly, while the remainder was lost gradually. The endogenous acyl donor present in the envelope fraction was shown to be membrane phospholipids. The acylation was not observed with free fatty acids prepared by alkaline hydrolysis of the phospholipids. Studies with purified phospholipids showed that the major phospholipids of E. coli (phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin) and phosphatidic acid acted as acyl donors. Thus, transacylation between diacylphospholipids and 2-acyl lysophospholipids catalyzed by E. coli envelopes was demonstrated.