PHOSPHATIDYLETHANOLAMINE N-METHYLTRANSFERASE FROM LIVER

Phosphatidylethanolamine N-methyltransferase (PEMT) converts phosphati dylethanolamine to phosphatidylcholine. Most PEMT activity (PEMT1) is associated with endoplasmic reticulum. A second form of the enzyme (PE MT2) 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 charact erized. The PEMT gene encodes both forms of the enzyme. Deletion of th e PEMT gene eliminates all activity in liver that converts phosphatidy lethanolamine to phosphatidylcholine. The activity of PEMT is regulate d by supply of the substrates, phosphatidylethanolamine and S-adenosyl methionine, and by the product S-adenosylhomocysteine. The expression of the gene is regulated during development and by the supply of choli ne in the diet. There is reciprocal regulation of the Kennedy pathway for phosphatidylcholine biosynthesis (via CDP-choline) and phosphatidy lethanolamine N-methyltransferase. Several experimental approaches sug gest that this enzyme might play a role in regulation of hepatocyte gr owth and cell division. (C) 1997 Elsevier Science B.V.