7, 8-Dihydropteroyl Oligo-γ-L-glutamates. Synthesis and kinetic studies with purified dihydrofolate reductase from mammalian sources

The synthesis of 7, 8-dihydropteroyl tri-, penta-, and heptaglutamate has been accomplished by standard solution peptide coupling, followed by dithionite reduction of the pterin moiety. These compounds were tested as substrates for dihydrofolate reductase (EC 1.5.1.3) obtained in highly purified form from four mammalian cell types: human acute myelogenous and acute lymphocytic leukemia cells, a methotrexate resistant murine L1210 leukemia, and erythrocytes from a patient with polycythemia vera treated with methotrexate. In general, the dihydro polyglutamates were as good as, or better substrates (lower K_m, higher V_max) than, the corresponding monoglutamate forms. These data, in conjunction with recent evidence demonstrating that intracellular folates exist predominantly as polyglutamate forms, strengthen the concept that folate polyglutamates may be the naturally occurring coenzymes in mammaliantissues.