Xanthine dehydrogenases

EC 1.1.1.204 designates the xanthine dehydrogenases, enzymes that turn hypoxanthine into xanthine and then oxidise xanthine on to uric acid, while also accepting a range of other purines and aldehydes as substrates. Dairy scientists know them as major proteins of the bovine milk fat globule membrane, and their activity shifts with heat treatment, which is why milk-processing research studies them as potential markers. The animal enzymes flip into the oxidase form after storage at −20 °C, or when treated with proteinases, organic solvents, or thiol reagents. Animal livers hold mainly the dehydrogenase form, while other tissues carry almost entirely the oxidase form, linking purine metabolism to dairy technology.