Standards; Amino Acids; Enzyme Activators and Inhibitors; Pharmaceutical/API Drug Impurities/Metabolites;
Aminopterin (Methotrexate EP Impurity B) is a folic acid antagonist. Its actively transported into cells by thefolate transporter. In the cell, its converted to a high molecular weight polyglutamate metabolite by folylpolyglutamate synthase, that, in turn, binds to dihydrofolate reductase and inhibits its activity.