ABSTRACT
The major phospholipids found in plant tissues are similar to those found in all eukaryotes, namely phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG), and diphosphatidylglycerol (DPG). The precursor molecule common to the de novo synthesis of all phospholipids in prokaryotes and eukaryotes is phosphatidic acid (PA). The enzyme cytidine diphosphate (CDP)-diacylglycerol synthase catalyzes the reaction between PA and CTP to yield CDP-1,2-diacylglycerol (DAG) and inorganic phosphate. In E. coli and yeast, PG is synthesized by a two-step reaction; CDP-diacylglycerol reacts with glycerol phosphate to yield phosphatidylglycerolphosphate and cytidine monophosphate (CMP), a reaction catalyzed by the enzyme glycerophosphate: CDP-diacylglycerol phosphatidyltransferase. In yeast, PS is synthesized from CDP-diacylglycerol and serine, a reaction catalyzed by the enzyme CDP-diacylglycerol:L-serine O-phosphatidyltransferase. The source of choline for the nucleotide pathway of PC biosynthesis is even less clear than the origin of free ethanolamine. Methylation of free ethanolamine to choline has not been conclusively demonstrated in any organism.
