Description_x000D_ General description_x000D_ Formerly E.C. 1.1.3.22_x000D_ Biochem/physiol Actions_x000D_ Although xanthine oxidase is found widely distributed in multiple tissues, it is highly expressed in endothelial and epithelial cells. Its expression was also increased in infected tissues where it was shown to have an anti-microbial effect due to its ability to generate reactive oxygen species._x000D_ Xanthine oxidase is a molybdenum-containing enzyme that is found in the cytosol, and may be strongly inhibited by flavonoids. It plays a vital role in the metabolism of some drugs, as well as purines and pyrimidines. It is also known to be a biological source of reactive oxygen species._x000D_ Unit Definition_x000D_ One unit will convert 1.0 μmole of xanthine to uric acid per min at pH 7.5 at 25 °C. Approx. 50% of the activity is obtained with hypoxanthine as substrate._x000D_ Physical form_x000D_ Suspension in 2.3 M (NH4)2SO4 containing 1 mM sodium salicylate_x000D_ Analysis Note_x000D_ Protein determined by biuret