Identification and properties of two methyltransferases in conversion of phosphatidylethanolamine to phosphatidylcholine.

Two methyltransferases involved in the methylation of phosphatidylethanolamine to form phosphatidylcholine were demonstrated in a microsomal fraction of bovine adrenal medulla. The first methyltransferase catalyzes the methylation of phosphatidylethanolamine to form phosphatidyl-N-monomethylethanolamine. This enzyme has an optimum pH of 6.5, a low Km for S-adenosyl-L-methionine (1.4 micron), and an absolute requirement for Mg2+. The second methyltransferase catalyzes the two successive methylations of phodphatidyl-N-monomethylethanolamine to phosphatidyl-N,N-dimethylethanolamine and phosphatidylcholine. In contrast to the first methyltransferase, it has an optimum pH of 10 and a high Km for S-adenosyl-L-methionine (0.1 mM) and does not require Mg2+.