Identification of 10-formyltetrahydrofolate dehydrogenase-hydrolase as a major folate binding protein in liver cytosol.

10-Formyltetrahydrofolate dehydrogenase (10-formyltetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.6) purified from pig liver contained bound tetrahydropteroylhexa-gamma-glutamate, a potent product inhibitor. Dehydrogenase purified from rat liver had chromatographic properties indistinguishable from those of a previously described major cytosolic folate binding protein of unknown function (Zamierowski, M.M. and Wagner, C. (1977) J. Biol. Chem. 252, 933-938; Cook, R.J. and Wagner, C. (1982) Biochemistry 21, 4427-4434). The dehydrogenase catalyzes the oxidative deformylation of 10-formyltetrahydrofolate to carbon dioxide and tetrahydrofolate. The tight binding of product to the enzyme suggests that oxidation of one-carbon moieties is regulated by the ratio of formyltetrahydrofolate to tetrahydrofolate in liver.