tailieunhanh - Báo cáo Y học: Phosphatidylinositol synthesis and exchange of the inositol head are catalysed by the single phosphatidylinositol synthase 1 from Arabidopsis

In order to study some of its enzymatic properties, phosphatidylinositol synthase 1 (AtPIS1) from the plant Arabidopsis thaliana was expressed in Escherichia coli, a host naturally devoid of phosphatidylinositol (PtdIns). In the context of the bacterial membrane and in addition to de novo synthesis, the plant enzyme is capable of catalysing the exchange of the inositol polar head for another inositol. Our data clearly show that the CDP-diacylglycerol-independent exchange reaction can occur using endogenous PtdIns molecular species or PtdIns molecular species from soybean added exogenously | Eur. J. Biochem. 269 2347-2352 2002 FEBS 2002 doi Phosphatidylinositol synthesis and exchange of the inositol head are catalysed by the single phosphatidylinositol synthase 1 from Arabidopsis Anne-Marie Justin Jean-Claude Kader and Sylvie Collin Universite Pierre et Marie Curie and CNRS Laboratoire de Physiologie Cellulaire et Moléculaire Paris France In order to study some of its enzymatic properties phosphatidylinositol synthase 1 AtPIS1 from the plant Arabidopsis thaliana was expressed in Escherichia coli a host naturally devoid of phosphatidylinositol PtdIns . In the context of the bacterial membrane and in addition to de novo synthesis the plant enzyme is capable of catalysing the exchange of the inositol polar head for another inositol. Our data clearly show that the CDP-diacylglychrol-independent exchange reaction can occur using endogenous PtdIns molecular species or PtdIns molecular species from soybean added exogenously. Exchange has been observed in the absence of cytidine monophosphate CMP but is greatly enhanced in the presence of 4 M CMP. Our data also show that AtPIS1 catalyses the removal of the polar head in the presence of much higher concentrations of CMP in a manner that suggests a reverse of synthesis. All of the PtdIns metabolizingactivities require free manganese ions. EDTA in the presence of low Mn2 concentrations also has an enhancing r n ertt. Keywords Arabidopsis exchange reaction phosphatidylinositol phospholipid synthesis reverse reaction synthase. Phosphatidylinositol PtdIns labelling has long been known to occur via two possible mechanisms a de novo synthesis catalysed by phosphatidylinositol synthase EC also known as CDP-diacylglycerol DAG myo-inositol 3-phosphatidyltransferase and an exchange reaction whereby the sugar head is exchanged between pre-existingPtdIns molecules and free inositol leadingin a test tube and in the absence of CDP-diacylglycerol CDP-DAG to the synthesis of labelled .