Reversal of Aminopterin Inhibition in the Chick Embryo with the Leuconostoc citrovorum Factor. ∗

Abstract

Summary

Concentrates of the Leuconostoc citrovorum factor (CF) and of “folinic acid” partially counteract the inhibitory action of aminopterin for the chick embryo. Folic acid and formylfolic acid were ineffective or only slightly effective under the same conditions. The magnitude of the effects obtained with CF were similar to those obtained previously with mixtures of thymidine and hypoxanthine desoxyriboside 1). The viewpoint is developed that conversion of folic acid to CF is a necessary preliminary to the catalytic action of the former compound, that synthesis of thymidine and one or more of the purine desoxyribosides are among the synthetic reactions for which CF or folic acid) is required, and that these synthetic reactions are those inhibited in the chick embryo by small amounts of aminopterin. The great variation that exists in the ability of CF to counteract aminopterin inhibition in various organisms is pointed out.