<prompt> Xanthine Oxidase is associated with which co-factor:ZincCopperSeleniumMolybdenum  <response>: Glutathione peroxidase contains selenium.Xanthine oxidase is large protein, having a molecular weight of 270,000, and has 2 flavin molecules bound as FAD, 2 molybdenum atoms and 8 iron atoms bound per enzymatic unit.The molybdenum atoms are contained as molybdopterin cofactors and are the active sites of the enzyme.The iron atoms are pa of 2Fe-2S ferredoxin iron-sulfur clusters and paicipate in electron transfer reactions 