Involved in the biosynthesis of the tuberculostearic acid (10-methylstearic-acid or TSA), a constituent lipid of the mycobacterial cell wall. Catalyzes the transfer of the methyl group from S-adenosyl-L-methionine (SAM) to the double bond of oleic acid in phosphatidylethanolamine or phosphatidylcholine to produce TSA. Inhibited by S-adenosyl-L-homocysteine. Optimum pH is 7-8. Lipid metabolism; fatty acid biosynthesis. Belongs to the CFA/CMAS family.