Effect of diet on choline phosphotransferase, phosphatidylethanolamine methyltransferase and phosphatidyldimethylethanolamine methyltransferase in liver microsomes

Phosphatidylcholine (PC) biosynthesis has been investigated in female rats fed a liquid amino acid, choline-methionine-free diet by assaying in liver microsomes the specific and total activities of choline phosphotransferase, phosphatidyldimethylethanolamine methyltransferase and phosphatidylethanolamine methyltransferase. There was a significant decrease in the specific activity (sp act) of choline phosphotransferase in the liver of rats fed a choline-methionine-free diet. The dietary omission of methionine for 2 wk resulted in a significant decrease in the sp act of choline phosphotransferase. The dietary omission of choline, methionine, B12, folic acid and the addition of a methyl group acceptor, guanidoacetic acid, decreased further the sp act of choline phosphotransferase. The phosphatidyl-ethanolamine methyltransferase sp act increased with the dietary omission of choline and methionine. The dietary omission of choline, methionine, B12, folic acid and the addition of a methyl group acceptor, guanidoacetic acid, resulted in a decrease in the sp act of phosphatidyldimethylethanolamine methyltransferase and an increase in phosphatidylethanolamine methyltransferase. The dietary omission of choline, methionine, B12, folic acid and the addition of a methylation inhibitor, 2-amino-2-methyl-1-propanol, did not result in a significant decrease in the sp act of choline phosphotransferase; however, it did significantly decrease the sp act of phosphatidylethanolamine methyltransferase. The addition of dietary methionine with the inhibitor resulted in a significant decrease in the sp act of the choline phosphotransferase and phosphatidylethanolamine methyltransferase when compared to control and/or when compared to deficient with or without inhibitor. The dietary supply of methionine, as a source of choline, did affect the activity of the enzymes that synthesize PC. The ratio of the substrate, S-adenosylmethionine, and the inhibitory product, S-adenosylhomocysteine, affected the enzymatic activity of phosphatidylethanolamine methyltransferase. It is suggested that the concentrations of these 2 compounds may be important in regulating the methylation of phosphatidylethanolamine in the liver cell.