Vitamin B12 and transmethylation in pig, chick, and rat liver homogenates.

The interrelationship of the requirement of choline, methionine, betaine, vitamin B12, and folic acid has been the subject of many recent investigations (2-5). That vitamin Blz functions in the intermediary metabolism of l-carbon units is also well recognized (1, 6-20, 21). However, while there have been several reports concerning the effect of the vitamin in viva and in vitro systems, the precise role of the vitamin in transmethylation reactions, in methyl synthesis, or in both, is still controversial. In earlier investigations from this laboratory (22, 23) it was shown that, on a synthetic milk diet containing 1.6 per cent methionine, the baby pig exhibited no demonstrable dietary choline requirement. Since a clear cut vitamin Blz deficiency can readily be produced in the baby pig (24, 25), the effect of this deficiency on the synthesis of choline in viva by transmethylation from methionine was studied. It was clearly shown that the vitamin was not involved in this direct transmethylation (19). The present experiments describe the formation in vitro of creatine and methionine in liver homogenates of these animals. Transmethylation reactions with normal and vitamin Blz-deficient chick and rat liver homogenates have also been examined.