caused by anionic membrane phospholipids. In the bacterium E. coli, phosphatidylethanolamine play a role in supporting lactose permeases active transport of lactose into the cell, and may play a role in other transport systems as well. Phosphatidylethanolamine plays a role in the assembly of lactose permease and other membrane proteins. It acts as a 'chaperone' to help the membrane proteins correctly fold their tertiary structures so that they can function properly. When phosphatidylethanolamine is not present, the transport proteins have incorrect tertiary structures and do not function correctly. Phosphatidylethanolamine also enables bacterial multidrug transporters to function properly and allows the formation of intermediates that are needed for the transporters to properly open and close. Structure As a lecithin, phosphatidylethanolamine consists of a combination of glycerol esterified with two fatty acids and phosphoric acid. Whereas the phosphate group is combined with choline in phosphatidylcholine, it is combined with the ethanolamine in phosphatidylethanolamine. The two fatty acids may be the same, or different, and are usually in the 1,2 positions (though they can be in the 1,3 positions). Synthesis The phosphatidylserine decarboxylation pathway and the cytidine diphosphate-ethanolamine pathways are used to synthesize phosphatidylethanolamine. Phosphatidylserine decarboxylase is the enzyme that is used to decarboxylate phosphatidylserine in the first pathway. The phosphatidylserine decarboxylation pathway is the main source of synthesis for phosphatidylethanolamine in the membranes of the mitochondria. Phosphatidylethanolamine produced in the mitochondrial membrane is also transported throughout the cell to other membranes for use. In a process that mirrors phosphatidylcholine synthesis, phosphatidylethanolamine is also made via the cytidine diphosphate-ethanolamine pathway, using ethanolamine as the substrate. Through several steps taking place in both the cytosol and endoplasmic reticulum, the synthesis pathway yields the end product of phosphatidylethanolamine. Phosphatidylethanolamine is also found abundantly in soy or egg lecithin and is produced commercially using chromatographic separation. Regulation Synthesis of phosphatidylethanolamine through the phosphatidylserine decarboxylation pathway occurs rapidly in the inner mitochondrial membrane. However, phosphatidylserine is made in the endoplasmic reticulum. Because of this, the transport of phosphatidylserine from the endoplasmic reticulum to the mitochondrial membrane and then to the inner mitochondrial membrane limits the rate of synthesis via this pathway. The mechanism for this transport is currently unknown but may play a role in the regulation of the rate of synthesis in this pathway. Presence in food, health issues Phosphatidylethanolamines in food break down to form phosphatidylethanolamine-linked Amadori products as a part of the Maillard reaction.