Effect of Folate Analogues on the Activity of Dihydrofolate Reductases and on the Growth of Plant Organisms

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Abstract
The inhibitory effect of antifolic agents of the 2,4-diaminopteridine group and the 2,4- diaminopyrimidine group was tested in vitro on dihydrofolate reductase and in vivo on growth of Zea mays, Pisum sativum, Neurospora crassa, and Euglena gracilis. Aminopterin and methotrexate, which belong to the former group, proved to be the most effective. The J50 values of these compounds were the same as those shown by enzymes of other sources and very similar for all the reductase enzymes tested, with the exception of the Euglena enzyme, which had an I50 about 100 times greater. For the second group of antifolic agents, trimethoprim and nine of its analogues were used. The I50 values of these compounds, compared to the first group, were generally different for all the reductases tested. These values had a wide range, which was sometimes as much as 7000:1. For both the classes examined the most potent inhibitors in vitro were the same as those in vivo. Moreover, the data indicate that 2,4-diaminopyrimidine derivatives can be useful to show different responses in plants to highly specific antifolic agents.

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