Incorporation rate in vitro of choline and methyl-methionine into human hepatic lecithins

In order to evaluate the quantitative role of cytidinediphosphate-choline and phosphatidyl-ethanolamine-methylation pathways in the synthesis of phosphatidylcholine in human liver tissue, the incorporation rate of [14C]choline and [14C]methyl-methionine into liver lecithins was determined. Liver biopsy was taken in 27 patients operated upon for uncomplicated gallstone disease. Linear incorporation into lecithin was achieved for N-methyl-methionine during 4 hours' incubation and for choline from 7.5 min to 60 min of incubation but with a significant positive Y-intercept. This Y-intercept was directly proportional to the concentration of choline in the medium and might be explained by a rapid base exchange between free choline in the medium and bases in phosphoglycerides. Fertile women showed significantly higher incorporation rate of methyl-methionine than postmenopausal women. Bile acids in the incubation medium did not influence the incorporation rate of thesebation medium did not influence the incorporation rate of these precursors into hepatic lecithin: The results indicate that the contribution of the methylation pathway in the synthesis of human liver lecithin accounts for about 10-15 per cent of that of the CDP-choline pathway.