The influence of folic acid upon enzyme systems in chick embryo liver.

The influence of folic acid upon various enzyme systems both in vivo and in vitro has recently been investigated by workers in several laboratories. In this laboratory it has been demonstrated that folic acid depresses xanthine oxidase activity when added to the enzyme systems in vitro (1) or when fed to chicks (2). It has also been shown that n-amino acid oxidase activity is decreased by dietary folic acid in the chick (2) and in the rat (3). Whereas endogenous respiration of liver is strongly inhibited by folic acid added to a liver homogenate in vitro (l), this effect was not observed when folic acid was fed to chicks (2). Dinning, Keith, and Day (4) have recently observed that aminopterin, an antimetabolite of folic acid, when fed to monkeys, causes a marked decrease in choline oxidase activity of the liver and kidney. Similar results were obtained in the monkey by a dietary restriction of folic acid. They suggest that folic acid functions as a constituent of the prosthetic group in the choline oxidase enzyme system. Investigating the effect of folic acid upon the hatchability of eggs, we have attempted to elucidate the mechanism by which hatchability is increased either by feeding folic acid to the hen or by injecting the vitamin into eggs produced by folic acid-deficient hens. The effect of folic acid on hatchability has previously been reported by Sunde et al. (5). In the present investigation the effects of folic acid on several liver enzyme systems of chick embryos have been studied. Because folic acid appears to function in purine metabolism, the effect of the vitamin on xanthine oxidase activity and uric acid content of embryo liver was studied. In order to observe the effects of the vitamin on what is believed to be a measure of general metabolic rate of the liver, endogenous respiration of the livers were determined. Since it has been observed that the ratio of liver weight to body weight in the chick is decreased by dietary folic acid (2, S),