Phosphatidylethanolamine (PE) is an important phospholipid that makes up cell membranes and organelle membranes. It is also called cephalin because it is abundant in the brain, spinal cord, and other nervous tissues. As much as 45% of brain phospholipids consist of cephalin. Cephalin is believed to play an important role in cognition and memory. In bacteria, phosphatidylethanolamine is the major phospholipid; in animals, lecithin or phosphatidylcholine is the most abundant, but cephalin is a close second.
Like phosphatidylcholine, phosphatidylethanolamine is composed of glycerol, two fatty acids, and phosphoric acid. While phosphatidylcholine has choline attached to the phosphate group, PE has ethanolamine. The fatty acids of PE may be identical or different, but they usually occupy the 1,2 carbon positions. At times, however, they may occupy the 1,3 carbon positions.
Animals and humans obtain most of the ethanolamine part of PE from dietary sources. The body then makes phosphatidylethanolamine through a series of enzymatic steps. First, ethanolamine is phosphorylated by a cytosolic enzyme called ethanolamine kinase. Second, the product of the first reaction is combined with cytidine triphosphate to create cytidine ethanolaminephosphotransferase. Finally, an enzyme bound to the endoplasmic reticulum membrane called cytidine diphospho-ethanolamine:diacylglycerol ethanolaminephosphotransferase acts on the product of the second reaction and on diacylglycerol to form PE.
The melting temperature of phosphatidylcholine is –20 degrees Celsius, while that of phosphatidylethanolamine is –16 degrees Celsius. PE has a higher melting point, so it is less fluid. Phosphatidylethanolamine is believed to lend a lateral pressure to the lipid bilayer, such that membrane proteins achieve their stable confirmation. It is also believed to support the positioning of positively charged amino acids on the inside of the membrane.
Phosphatidylethanolamine has many other biological roles. It helps stabilize the sarcolemmal membranes of the cardiac tissues when there is an inadequate supply of oxygen, such as what happens in coronary heart disease. PE also plays a role in the hepatic secretion of very-low-density lipoproteins as well as in membrane fission and fusion. It undergoes reactions to donate its ethanolamine component for the production of a membrane protein-anchoring compound called glycosylphosphatidylinositol. PE can also be converted to phosphatidylcholine by phosphatidyl ethanolamine methyltransferase, an enzyme present in the liver.
Cephalin is postulated to play a main role in keeping the nervous system intact and healthy because of its multitude of functions and its significant contribution to neural tissues. Some supplements containing this phospholipid are available on the market. There is no firm basis regarding the effectiveness of these supplements in maintaining and restoring the health of the nervous system, or in serving as memory enhancers.