Dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase) catalyzes the NADPH-dependent reduction of 7,8-dihydrofolate (H2F) to 5,6,7,8-tetrahydrofolate (H4F). This enzyme is necessary for maintaining intracellular pools of H4F and its derivatives, which are essential cofactors in the one-carbon transfer reactions utilized in the biosynthesis of purines, thymidylate, and several amino acids. It is also the target enzyme for antifolate drugs such as the antineoplastic drug methotrexate (MTX) and the antibacterial drug trimethoprim (Scheme 1). Because of its biological and pharmacological importance, dihydrofolate reductase (DHFR) has been the subject of intensive structural and kinetic studies (Blakley, 1985). The structures of the Escherichia coli and the Lactobacillus casei enzymes have been determined to 1.7 Å for several binary and ternary complexes containing MTX and/or NADP+ (Bolin et al., 1982; Filman et al., 1982; Matthews et al., 1985). The primary sequences of DHFR for eight bacterial and vertebrate sources are also available for comparison (Blakley, 1985). In addition, a complete kinetic scheme for wild-type E. coil DHFR has been derived from pre-steady-state and steady-state kinetics (Fierke et al., 1987).
KeywordsTernary Complex Dihydrofolate Reductase Dissociation Rate Constant Hydride Transfer Antifolate Drug
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