Metabolism of dihydroaminopterin and the influence of aminopterin and related derivatives on the metabolism of (-)-5-formyl-tetrahydrofolic acid in Pediococcus cerevisiae.

[3H]Dihydroaminopterin, but not [3H]methotrexate or [3H]aminopterin, was rapidly taken up by resting cell of Pediococcus cerevisiae and inhibited the uptake of (-)-5-formyl-tetrahydrofolic acid to more than 90% at a concentration of 25 muM. On the other hand 5-formyl-tetrahydrofolic acid inhibited the uptake of dihydroaminopterin to a similar extent. Dihydroaminopterin was metabolized by Pediococcus cerevisiae, but not by Lactobacillus casei, to a compound tentatively identified as dihydroaminopterin diglutamate. Methotrexate or aminopterin at a concentration of 25 muM did not inhibit the uptake of 5-formyl-tetrahydrofolic acid in Pediococcus cervisiae, but inhibited the conversion of this compound to polyglutamate forms almost completely at a level of 2.5 mu M.