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.     

Determination of creatine kinase isoenzyme MB activity in serum using immunological inhibition of creatine kinase M subunit activity. Activity kinetics and diagnostic significance in myocardial infarction.

This is a new method for the determination of creatine kinase isoenzyme MB activity in serum. The method uses direct activity measurement of creatine kinase B subunit activity after blocking of CK-M subunit activity by inhibiting antibodies. The test takes no longer than 15 min. The method yields an intra-serial C.V. of 2.0-12.9%, and a C.V. from day to day of 5.5%. The detection limit is 3.4 U/l creatine kinase MB. In the 95 cases with proven myocardial infarction several types of creatine kinase MB activity kinetics could be determined. The percentage of creatine kinase MB of peak CK-total is 6-25%, with a mean of 11.1%. The amount of creatine kinase MB with respect to total CK activity after reinfarction is higher than the amount after initial infarction.     

Carbon tetrachloride depresses hepatic phospholipid synthesis in rats

40 h after an acute dose of CCl4 (11.3 mmol/kg), the incorporation of [1-3H]ethanolamine into rat hepatic microsomal phospholipids was inhibited to 70% of control. Incorporation into phospholipids of the inner and outer mitochondrial membranes was 30-35% of control. Rates of incorporation were equal to or above normal rates in all membranes 65 h after dosage. The activity of methyltransferase in microsomal fractions isolated from rats 10 to 66 h after dosage was depressed. These data suggest that the alteration of mitochondrial phospholipids that parallels mitochondrial dysfunction after acute CCl4 dosage could be attributed to a CCl4-induced inhibition of the microsomal phospholipid biosynthetic pathways.