Inhibition of nucleic acid synthesis by folic acid antagonists.

Woolley and Pringle (13) have recently reported the formation of 4-amino-5-carboxamidoimidazole during growth of Escherichia coli in the presence of 4-aminopteroylglutainic acid (aminopterin). Some of us have observed that excessive doses of folie acid speed up the leukemic process in mice and that folie acid will reverse the well known antileukemic action of aminopterin (11). This reversal of the anti-leukemic action of folie acid antagonists by means of large doses of folie acid had previously been reported by Burchenal (4) and Law (7). In the face of the above information, the sugges tion that formyl folie acid might be involved in in-