In vivo and In vitro Conversion of Folic Acid to Citrovorum Factor by Rat.

Abstract
Rat liver contains an enzyme system which converts pteroylglutamic acid (PGA) to citrovorum factor (CF). Dietary homocysteine and cysteine enhance the urinary excretion of CF by rats receiving PGA, the former more so than the latter. In vitro conversion of PGA to CF by rat liver homogenate is enhanced by homocysteine, serine and formate. The stimulatory effect of homocysteine on CF synthesis is enhanced by added serine, but inhibited by added formate.