Аннотация:It was discovered than the tungsten and rhenium content in the enzyme xantine oxidase (XO) is relatively lower than the molybdenum one. The tungsten quantity as observed in the purified fraction of the enzyme is reduced compared to the metal content in the substrate (e.g., in buttermilk). In a sample of milk cows XO from Unal (lead hyper-province) also found lead. In the process of the isolated enzyme storage, its portion is hydrolyzed to its subunits, since when carrying out HPLC of the enzyme some peaks corresponding to the molecular weights of 130 and 40 kDa appear on the chromatograms, which is consistent with the existing data.