Multiple folate-dependent enzymes

Multiple folate-dependent enzymes represent a critical metabolic network involved in one-carbon transfer reactions necessary for the de novo synthesis of purine and pyrimidine nucleotides (StatPearls, 2023). The primary enzymes in this group include dihydrofolate reductase (DHFR), thymidylate synthase (TYMS), and enzymes of the purine biosynthetic pathway such as phosphoribosylaminoimidazolecarboxamide formyltransferase (ATIC) (NIH, 2024). These enzymes are essential for DNA replication and cell division, making them vital targets in rapidly proliferating cells. Methotrexate, a classic antifolate, exerts its therapeutic effect by competitively inhibiting DHFR, thereby depleting the pool of tetrahydrofolate required for nucleotide synthesis (PubChem, CID 126941). In addition to DHFR inhibition, methotrexate is converted into polyglutamate forms within cells, which extend its duration of action and allow for the direct inhibition of TYMS and ATIC. This multi-enzyme inhibition leads to the arrest of the S-phase of the cell cycle and eventual apoptosis, providing the basis for its use in treating various malignancies and autoimmune conditions like rheumatoid arthritis (PubMed, PMID: 16265537). The inhibition of these enzymes also results in the accumulation of adenosine, which contributes to the anti-inflammatory effects observed in rheumatologic applications.

Other names

Folate-dependent enzymesFolate metabolism enzymesMethotrexate targets

Methotrexate acts as a folate antagonist, primarily inhibiting dihydrofolate reductase (DHFR), which prevents the conversion of dihydrofolate to tetrahydrofolate (StatPearls, 2023). This depletion of reduced folates halts the synthesis of thymidylate and purine nucleotides. Additionally, methotrexate undergoes intracellular polyglutamylation; these polyglutamated forms directly inhibit other folate-dependent enzymes, including thymidylate synthase (TYMS) and enzymes involved in de novo purine synthesis like phosphoribosylaminoimidazolecarboxamide formyltransferase (ATIC) (PubChem, CID 126941; Cronstein, 2005).