Methotrexate is a competitive inhibitor of DHFR. It binds to the active site of the enzyme, preventing the binding of dihydrofolate. The binding affinity of methotrexate to DHFR is significantly higher than that of its natural substrate, dihydrofolate. This binding disrupts the enzymeâs normal function, leading to a decrease in the production of tetrahydrofolate and, consequently, a reduction in DNA synthesis.
