Phosphatidylethanolamines (PE) are a class of phospholipids that incorporate a phosphoric acid headgroup into a diacylglycerol backbone. They are the second most abundant phospholipid in eukaryotic cell membranes, and contrary to phosphatidylcholine, it is concentrated with phosphatidylserine in the cell membrane's inner leaflet. In Arabidopsis thaliana, there exist two phosphatidylethanolamine biosynthesis pathways. The first pathway consists of mainly enzymes localized to either the cytosol or the cell membrane. Cell membrane-localized enzymes in this pathway are not drawn as such for clarity. Instead, they are indicated with a dark green colour and appear to be free floating in the cytosol. This first pathway begins with serine decarboxylase catalyzing the biosynthesis of ethanolamine from serine. It requires pyridoxal 5'-phosphate as a cofactor. Next, choline/ethanolamine kinase, localized to the cell membrane, catalyzes the conversion of ethanolamine to phosphoethanolamine. Then ethanolamine-phosphate cytidylyltransferase, localized to the mitochondria outer membrane, catalyzes the conversion of phosphoethanolamine to CDP-ethanolamine. Last, choline/ethanolaminephosphotransferase, localized to the cell membrane, catalyzes phosphatidylethanolamine CDP-ethanolamine, respectively. The second pathway consists of mainly enzymes localized to the endoplasmic reticulum membrane (also depicted in dark green in the image. Beginning in the cytosol, glycerol-3-phosphate dehydrogenase [NAD(+)] catalyzes the interconversion of glycerone phosphate (from glycolysis) and glycerol 3-phosphate. After glycerol 3-phosphate enters the endoplasmic reticulum, glycerol-3-phosphate acyltransferase esterifies the acyl-group from acyl-CoA to the sn-1 position of glycerol-3-phosphate. Third, 1-acyl-sn-glycerol-3-phosphate acyltransferase 2 catalyzes the conversion of lysophosphatidic acid (LPA or 1-acyl-sn-glycerol 3-phosphate) into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by incorporating an acyl moiety at the 2nd position. Fourth, phosphatidate cytidylyltransferase catalyzes the conversion of a 1,2-diacyl-sn-glycerol 3-phosphate into a CDP-diacylglycerol. It requires a magnesium ion as a cofactor. Fifth, CDP-diacylglycerol--serine O-phosphatidyltransferase catalyzes the synthesis of phosphatidylserine from L-serine and a CDP-diacylglycerol. Last, phosphatidylserine decarboxylase catalyzes the formation of phosphatidylethanolamine from phosphatidylserine. It requires pyruvate as a cofactor.

Phosphatidylethanolamine Biosynthesis PE(18:3(9Z,12Z,15Z)/22:0) References