The nitrate reductase activity of milk xanthine oxidase

J Appl Biochem. 1985 Apr;7(2):86-92.


Milk xanthine oxidase oxidizes xanthine at pH 9.6 and reduces nitrates at pH 5.2. It is shown that the nitrate reductase activity requires molybdenum and sulfur-containing sites in the enzyme, whereas oxidation of xanthine also requires iron-containing sites and FAD. As the pH changes from 5.2 to 9.6, the conformation of the enzyme molecule is modified as demonstrated by changes in the absorption, fluorescence, and circular dichroism spectra. When the enzyme is treated with dithioerythritol, it may pass from the oxidase to the dehydrogenase form with a marked increase in the nitrate reductase activity.

MeSH terms

  • Animals
  • Calcium Chloride / pharmacology
  • Cattle
  • Chloromercuribenzoates / pharmacology
  • Dithioerythritol / pharmacology
  • Flavin-Adenine Dinucleotide / metabolism
  • Hot Temperature
  • Hydrogen-Ion Concentration
  • Milk / enzymology*
  • Nitrate Reductases / metabolism*
  • Protein Conformation
  • Xanthine Oxidase / metabolism*
  • p-Chloromercuribenzoic Acid


  • Chloromercuribenzoates
  • Flavin-Adenine Dinucleotide
  • p-Chloromercuribenzoic Acid
  • Dithioerythritol
  • Xanthine Oxidase
  • Nitrate Reductases
  • Calcium Chloride