IV. BIOCHEMICAL SYSTEMS 37 



Evidence was presented by Williams^ ^* demonstrating a positive con- 

 nection between the choline oxidase system of rat hver and the probable 

 precursors of the Leuconostoc citrovorum factor (LCF) as well as LCF itself. 

 It was shown that when ascorbic acid and folic acid were incubated with 

 rat liver homogenate small but significant stimulation of the choline oxidase 

 system was observed. This effect was more pronounced in rats fed 

 aminopterin. Since aminopterin is believed to inhibit the conversion of folic 

 acid to LCFji^^ Williams^^* postulated that the stimulatory effect of the 

 folic acid and ascorbic acid added in vitro was due to the enzymatic con- 

 version of these substances to LCF, which was actually responsible for 

 stimulation of the enzyme system. In work that followed, WilHams^^^ studied 

 various combinations of factors related to LCF, e.g., folic acid, ascorbic 

 acid, vitamin B12, and synthetic LCF itself in relation to choline oxidase. 

 This work was done with a modified enzyme system containing homocys- 

 teine which amplified the effects of the above factors. The results of this 

 investigation showed that folic acid, Leuconostoc citrovorum factor, vitamin 

 B12, and ascorbic acid individually or in combination markedly stimulate 

 choline oxidation in the liver homogenates of rats fed aminopterin. Only 

 ascorbic acid and folic acid were found to stimulate choline oxidation in 

 normal rat liver homogenates. The stimulation by these factors was ob- 

 served to be much more marked in aminopterin-fed rats. 



Williams et aU^'^^ subsequently noted that folic and folinic acids in whole 

 liver and in isolated mitochondria were markedly decreased in folic acid 

 deficiency in rats. Aminopterin-fed animals showed a similar decrease in 

 folinic acid, but there was no effect on the folic acid content of the liver or 

 of the mitochondrial fraction. The loss in choline oxidase activity in the 

 latter fraction paralleled the disappearance of folinic acid, and it was con- 

 cluded that this substance rather than folic acid was involved in the main- 

 tenance of choline oxidase activity. 



The influence of several dietary factors on tissue choline oxidase has been 

 reported. The removal of folic acid from the diet of the monkey or the 

 administration of aminopterin to this animal eliminated most of the choline 

 oxidase activity from the liver and kidney.'" Further studies disclosed 

 that aminopterin-treated chickens did not exhibit the choline oxidase ac- 

 tivity normally found in bone marrow,'®^ and that livers from folic acid- 

 deficient chicks oxidized choline at a reduced rate.'^^ Chick kidney choline 

 oxidase was not found to be significantly reduced in folic acid deficiency. 



1" J. N. Williams, Jr., J. Biol. Chem. 191, 123 (1951). 



186 C. A. Nichol and A. D. Welch, Proc. Soc. Exptl. Biol. Med. 74, 52, 403 (1950). 



16' J. N. Williams, Jr., J. Biol. Chem. 192, 81 (1951). 



i"a J. N. Williams, Jr., A. Sreenivasan, Shan-Ching Sung, and C. A. Elvehjem, J. 



Biol. Chem. 202, 233 (1953). 

 1" J. S. Dinning, C. K. Keith, P. L. Davis, and P. L. Day, Arch. Biochem. 27, 89 



(1950). 



