Catalyzes the first step of the methylation pathway of phosphatidylcholine biosynthesis, the SAM-dependent methylation of phosphatidylethanolamine (PE) to phosphatidylmonomethylethanolamine (PMME). Preferentially converts di-C16:1 substrates. a 1,2-diacyl-sn-glycero-3-phosphoethanolamine + S-adenosyl-L-methionine = 1,2-diacyl-sn-glycero-3-phospho-N-methylethanolamine + H(+) + S-adenosyl-L-homocysteine Optimum pH is 9.9. Phospholipid metabolism; phosphatidylcholine biosynthesis. Repressed by myo-inositol and choline. Present with 1810 molecules/cell in log phase SD medium. Belongs to the class VI-like SAM-binding methyltransferase superfamily. CHO2 family.