Phosphatidylethanolamine N-methyltransferase from rat liver

Phosphatidylethanolamine N-methyltransferase (PEMT) is an enzyme of the endoplasmic reticulum that catalyzes the synthesis of phosphatidylcholine by transfer of three methyl groups from S-adenosyl-L-methionine to the amino head-group of phosphatidylethanolamine (PE). The major route for phosphatidylcholine (PC) synthesis in most cells is via the CDPcholine pathway. However, by some estimates, PE methylation is responsible for 15–20% of PC synthesis in the liver. PE methylation activity is very low in extrahepatic tissues, and it is generally assumed that this pathway does not contribute significantly to PC synthesis. Evaluation of the function of PE-derived PC in hepatic metabolism has been aided by the purification and characterization of rat liver PEMT. PEMT purified by the procedure described in this chapter is homogeneous as determined by gel electrophoresis and displays kinetic properties consistent with an enzyme that acts on mixed micellar substrates.