Occurrence of Independent Systems for the Cleavage of Folic Acid and Citrovorum Factor in Rat Liver

Abstract

RECENT work has demonstrated that extracts from animal tissues can actively degrade folic acid^1,2 and citrovorum factor³ at the C₉—N₁₀ linkage with the liberation of a diazotizable amine. Whether the same enzyme systems are involved in the cleavage of the two substrates is, however, not established. The horse-liver fraction which has been shown to degrade citrovorum factor was inactive towards folic acid³. In a recent paper, Dinning et al. ⁴ have suggested that the transformation of folic acid into a diazotizable amine by slices and homogenates of rat livers takes place with the intermediate formation of citrovorum factor. In the course of studies on folic acid degradation by purified fractions from rat liver, we prepared extracts which degrade folic acid but not citrovorum factor. Furthermore, A-methopterin has been found to inhibit selectively the cleavage of folid acid in acetone-dried powder extracts, but the citrovorum factor remains unaffected.