Comparison of phospholipid N-methylation activity in rat submandibular salivary gland and liver.

Successive phospholipid N-methylation from phosphatidylcholine to phosphatidylethanolamine in submandibular gland and liver microsomes proceeded without the addition of exogenous phospholipid substrate. Methylation activity in the submandibular microsomes showed different susceptibilities to various detergents than the liver enzyme and also partially required Mg2+. However, the three methylation steps could not be distinguished by their Mg2+ requirements. Ca2+ had no effect on the activity. The methylation activity in submandibular gland was much lower than in liver. Chronic administration of isoproterenol, which causes an increase of phosphatidylcholine in membrane phospholipids of salivary glands, decreased methylation activity in the submandibular gland. Thus the increase in phosphatidylcholine in isoproterenol-treated rat salivary glands may not be derived from the phospholipid methylation pathway, but may be due to stimulation of other routes of phosphatidylcholine metabolism.