Phosphatidylethanolamine is the most abundant phospholipid in prokaryotes and the second most abundant found in the membrane of mammalian, plant, and yeast cells, comprising approximately 25% of total mammalian phospholipids. In the brain, phosphatidylethanolamine comprises almost half of the total phospholipids. It is synthesized mainly through the cytidine diphosphate-ethanolamine and phosphatidylserine decarboxylation pathways, which occur in the endoplasmic reticulum (ER) and mitochondrial membranes, respectively. It is a precursor in the synthesis of phosphatidylcholine and arachidonoyl ethanolamide and is a source of ethanolamine used in various cellular functions. In E. coli, phosphatidylethanolamine deficiency prevents proper assembly of lactose permease, suggesting a role as a lipid chaperone. It is a cofactor in the propagation of prions in vitro and can convert recombinant mammalian proteins into infectious molecules even in the absence of RNA. Phosphatidylethanolamines (egg) is a mixture of phosphatidylethanolamines isolated from egg with various fatty acyl groups at the sn-1 and sn-2 positions.