Selection of Methotrexate-Resistant Lactobacillus Casei in the Presence of Folate or 5-Formyl-Tetrahydrofolate Affects the Resistance Mechanism
Reduced folate cofactors (H4PteGlu) are essential for the biosynthesis of purines, thymidine and some amino acids, thus the antimetabolites blocking their biochemical pathways (1) have been used as effective chemotherapeutics. Methotrexate (MTX), a classical antifolate inhibits the activity of dihydrofolate reductase (DHFR), consequently causing a depletion of cellular tetrahydrofolate cofactors, which results cessation of all the H4PteGlu-dependent processes. Intracellular retention and affinity of folates and MTX to target enzymes is determined by the activity of folylpolyglutamate synthetase (FPGS), which catalyses a MgATP-dependent attachment of glutamate residues to the glutamate of folates and the analogs (2,3). Another enzyme affecting the intracellular availability of the polyglutamylated folates is γ-glutamyl hydrolase (GH), which cleaves the linked polyglutamates (2,4). The biological effect of folates and the analogs thus strongly depends upon the activity of FPGS versus GH (4,5).
KeywordsPermeability Catalysis Barium Methotrexate Folate
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