What is "xanthine oxidase"

n. (context enzyme English) A crystallizable flavoprotein enzyme containing iron and molybdenum that promotes the oxidation especially of hypoxanthine and xanthine to uric acid and of many aldehydes to carboxylic acids and that is obtained usually from milk or liver

Xanthine oxidase (XO, sometimes 'XAO') is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species. These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. These enzymes play an important role in the catabolism of purines in some species, including humans.

Xanthine oxidase is defined as an enzyme activity (EC 1.17.3.2). The same protein, which in humans has the HGNC approved gene symbol XDH, can also have xanthine dehydrogenase activity (EC 1.17.1.4). Most of the protein in the liver exists in a form with xanthine dehydrogenase activity, but it can be converted to xanthine oxidase by reversible sulfhydryl oxidation or by irreversible proteolytic modification.