Effect of Nucleic Acid Derivatives in the Reversal of Aminopterin Inhibition in the Chick Embryo.

Abstract

Several purine bases and related nucleosides were tested for their effectiveness in potentiating the reversal by thymidine of aminopterin inhibition of the chick embryo. Of the free purine bases, hypozanthine was most active; adenine and guanine less so, but xanthine was inactive. Of the nucleosides tested, inosine alone was active, being even more so than hypoxanthine; together with thymidine it completely overcame the effects of the low level of aminopterin employed. Aminopterin apparently blocks embryonic growth by preventing synthesis of compounds essential for the formation of nucleic acids; when these substances are supplied preformed, growth occurs even though aminopterin is present.