Relation of dietary folic acid and vitamin B12 to enzyme activity in the chick.

The relationship of folic acid (PGA) to certain enzyme systems has recently been the subject of investigation by workers in several laboratories. In 1948 Kalckar and Klenow (l-3) demonstrated the inhibitory effect of folic acid upon milk xanthopterin oxidase in vitro. Subsequently Keith et al. (4), studying the effect of dietary PGA upon enzymes, observed that activity of xanthine oxidase in chick liver was strongly depressed as the concentration of folic acid was increased in the ration. Quite recently Kelley (5) observed that rat liver n-amino acid oxidase activity was decreased to some extent by feeding PGA. Although the relationship of folic acid and vitamin B12 to hemoglobin production is quite well known (6), some of the basic metabolic functions of these two vitamins, particularly of vitamin B12, are at present obscure. In view of this information the effects of variations in dietary intake of vitamin Blz and folic acid on the following enzyme systems were investigated: xanthine oxidase, n-amino acid oxidase, endogenous respiration, and catalase. Since we have experimental evidence’ that folic acid strongly inhibits endogenous respiration of rat liver in vitro, the effects of dietary folic acid and vitamin RI2 upon endogenous oxidative activity have been studied. The influence of the two vitamins in question upon liver catalase activity has been invest.igated for several reasons. First, the porphyrin group is common to both catalase and hemoglobin; second, catalase destroys metabolic hydrogen peroxide, which is produced by oxidation of n-amino acids and xanthine; and third, metabolic hydrogen peroxide is believed to be involved in the destruction of hemoglobin (7). As a preliminary investigation into the metabolic disorder producing paralytic symptoms in chicks on a folic acid-deficient diet containing