Effect of choline deficiency on utilization of labeled precursors of choline and turnover of choline in the liver of mature Japanese quail.

Studies were conducted to determine the effect of choline deficiency on utilization of various labeled precursors of choline and rate of choline biosynthesis in mature Japanese quail. A deficiency of dietary choline did not change the in vivo incorporation of 14C-label from (1,2-14C) ETHANOLAMINE, N, N-dimethyl (1,2-14C) ethanolamine, and L-(methyl-14C) methionine into liver phosphatidylcholine (PC) or total phospholipids. Incorporation of radioactivity from (14C) serine into liver PC was increased, but the difference was not significant (PGREATER THAN3.35). In vitro studies confirmed these observations as there were no differences in liver microsomal methyltransferase activities, expressed as the incorporation of methyl-14C from labeled S-adenosylmethionine into microsomal PC from quail fed a purified diet with with or without choline. Rats appeared to incorporate an increased amount of 14C into PC when fed a diet devoid of choline, but the differences were not significant. There were differences in methyltransferase activities among species, and quail had the lowest activity. A slower turnover of choline was found in quail liver (t1/2=7.5 hours) as compared with that of hen liver (t1/2=2.0 hours). The methyltransferase responsible for the first methylation of phosphatidyl-ethanolamine from quail liver appears to differ from most other biosynthetic enzymes in that it occurs in liver and catalyzes the reaction at a slow rate but cannot adapt to exogenous choline supply to meet the requirements for normal bodily functions in quail.