Mechanism of the Enzymatic Synthesis of Cardiolipin in Escherichia coli

In previous studies, the enzymatic conversion of phosphatidylglycerol to cardiolipin (diphosphatidylglycerol) in cell-free preparations from E. coli was shown to be stimulated by the addition of CDP-dipalmitin, suggesting the participation of the cytidine coenzyme as phosphatidyl donor. The present communication, however, presents three lines of evidence supporting the following mechanism for the synthesis of cardiolipin in E. coli.2 Phosphatidylglycerol --> cardiolipin + glycerolWhen CDP-dipalmitin labeled with (32)P in the phosphatidyl moiety was incubated with phosphatidyl[2-(3)H]-glycerol, the cardiolipin produced in the enzymatic reaction was labeled with tritium, but not with (32)P. Thus, CDP-diglyceride stimulates the reaction but does not participate as phosphatidyl donor. When [(28)P]phosphatidyl[2-(3)H]glycerol was used as substrate, the ratio of tritium to (32)P in the cardiolipin product was only half of that in the starting phosphatidylglycerol, consistent with the elimination of 1 mol of glycerol during conversion to cardiolipin. Finally, free glycerol produced during the reaction has been unambiguously identified by phosphorylation with ATP in a reaction catalyzed by glycerol kinase (EC 2.7.1.30), followed by chromatographic isolation of labeled sn-3-glycero-3-phosphate.