Phosphatidylethanolamine methylation in intestinal brush border membranes from rats resistant to Trichinella spiralis.

Methylation of phospholipids is proposed as a mechanism to explain changes in properties of intestinal brush border membrane that coincide with development of immunity to the intraepithelial parasite, Trichinella spiralis. Methylation was measured by the incorporation of the [3H]methyl group from S-adenosyl-L-[3H]methyl methionine into phospholipids. At least two enzymatic components were detected that converted phosphatidylethanolamine to phosphatidylcholine. The first, designated methyltransferase I, catalyzed the formation of phosphatidylmonomethylethanolamine from phosphatidylethanolamine and had a low Km for S-adenosyl-L-methyl-methionine (5 microM). The second, designated methyltransferase II, which catalyzed the methylation of phosphatidylmonomethylethanolamine to phosphatidyldimethylethanolamine and phosphatidyldimethylethanolamine to phosphatidylcholine, had a high Km for S-adenosyl-L-methyl methionine (167 microM). Both enzymes had two pH optima, were most active at 37 degrees C and were Mg2+ dependent. A decrease in methylation activity was present in brush border membranes from rats immunized against T. spiralis. Although the synthesis of phosphatidylcholine was not significantly altered there was a substantial decrease in the formation of phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine as compared with nonimmunized rats. Since phospholipid composition influences membrane fluidity and cell function, it is proposed that altered methylation activity may influence the characteristics of brush border membrane in the immune host.