Phosphatidylethanolamine N-methyltransferase from liver.

Phosphatidylethanolamine N-methyltransferase (PEMT) converts phosphatidylethanolamine to phosphatidylcholine. Most PEMT activity (PEMT1) is associated with endoplasmic reticulum. A second form of the enzyme (PEMT2) has been localized to the mitochondria-associated membrane. PEMT2 is a 22.5-kDa protein that has been purified from rat liver. The rat liver PEMT2 cDNA and the murine PEMT gene have been cloned and characterized. The PEMT gene encodes both forms of the enzyme. Deletion of the PEMT gene eliminates all activity in liver that converts phosphatidylethanolamine to phosphatidylcholine. The activity of PEMT is regulated by supply of the substrates, phosphatidylethanolamine and S-adenosylmethionine, and by the product S-adenosylhomocysteine. The expression of the gene is regulated during development and by the supply of choline in the diet. There is reciprocal regulation of the Kennedy pathway for phosphatidylcholine biosynthesis (via CDP-choline) and phosphatidylethanolamine N-methyltransferase. Several experimental approaches suggest that this enzyme might play a role in regulation of hepatocyte growth and cell division.