A Dpnh-Specific Nitrate Reductase From Germinating Wheat

Abstract

The isolation and purification of a nitrate reductase from the embryos of germinating wheat is described. This is a soluble enzyme, which is coupled specifically to reduced diphosphopyridine nucleotide (DPNH). Addition of flavin adenine dinucleotide to the purified enzyme results in a three-fold increase in activity. Flavin mononucleotide is without effect. Potassium cyanide and sodium azide cause 50 per cent. inhibition of enzyme activity at 1· 6 X IO-6M and 2 X IO-5M respectively. The effect of a range of other inhibitors is reported. The presence of inorganic phosphate is required for maximum activity. The dissociation constant (Ks ) of the nitrate-enzyme complex is 3·8 X IO-4M, and that of the DPNH-enzyme complex is 8 X IO-6M. The pH optimum for enzymatic activity is 7 ·4.