PURIFICATION AND PROPERTIES OF PHOSPHATIDYL-N-MONOMETHYLETHANOLAMINE N-METHYLTRANSFERASE, THE ENZYME CATALYZING THE SECOND AND THE THIRD STEPS IN THE PHOSPHATIDYLETHANOLAMINE N-METHYLTRANSFERASE SYSTEM, FROM MOUSE LIVER MICROSOMES

Abstract

The phosphatidylethanolamine (PE) N-methyltransferase (MT) system is known to convert PE to phosphatidylcholine by three successive N-methylations. Phosphatidyl-N-monomethylethanolamine (PME) MT was purified 1, 400-fold from mouse liver microsomes and separated from the PE-MT activity for the first time. This enzyme catalyzes N-methylations of PME and phosphatidyl-N, N-dimethylethanolamine, the intermediates of PE-MT system, but not PE, the initial substrate of the PE-MT system. In addition, a preparation with a different affinity to S-adenosyl-L-homocysteine catalyzing all the three methylations was obtained. These results suggest that at least two enzymes are involved in the PE-MT system.