Bovine dihydropteridine reductase

Dihydropteridine reductase has been purified to homogeneity from bovine liver and bovine adrenal medulla by precipitation with polyethylene glycol, ion exchange chromatography, gel filtration, and affinity chromatography on 5-AMP-Sepharose 4B. The enzymes from the two tissues seem identical by the criteria of gel filtration chromatography, affinity chromatography, polyacrylamide gel electrophoresis in the presence and absence of dodecyl sulfate, isoelectric focusing, amino acid analysis, and binding of NADH. Fluorescence studies show two independent binding sites for NADH and a dissociation constant of 10 nM at pH 6.8. Isoelectric focusing of the enzyme as purified in the presence of NADH revealed three different bands, which by removal of this coenzyme were converted into a single band, corresponding to pI 5.7. The enzyme contains no carbohydrate or zinc.