Effect of Friend virus infection on the biosynthetic enzymes of phosphatidylcholine biosynthesis in spleen microsomes.

The effects of Friend virus infection on phosphatidylethanolamine methyltransferase, phosphatidylmonomethylethanolamine methyltransferase, phosphatidyldimethylethanolamine methyltransferase and choline phosphotransferase in mouse spleen microsomes were investigated 14 days following viral inoculation. There was a significant 9.2 fold increase above control values in the specific activity (pmol phosphatidylcholine formed/min/mg microsomal proteins) of choline phosphotransferase. No stimulation occurred in the activities of phosphatidylethanolamine methyltransferase, phosphatidylmonomethylethanolamine methyltransferase or phosphatidyldimethylethanolamine methyltransferase, the three enzymes involved in the methylation phosphatidylethanolamine (PE) to phosphatidylcholine (PC). The concentration of S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy), the substrate and physiological inhibitor of transmethylation reactions, respectively, were measured in the spleens of control and viral infected mice. AdoHcy is a competitive inhibitor of the phosphatidylethanolamine methyltransferase. A significant increase in the AdoHcy concentration and the resultant decrease in the AdoMet/AdoHcy ratio are sufficient to prevent stimulation of the transmethylation of PE to PC.