Xanthine oxidase
…and each subunit has a molecular weight of roughly 145 kDa. Each active site consists of a flavin molecule (bound as FAD), a Moco cofactor containing a molybdenum atom, and 2 [2Fe-2S] clusters containing 4 iron atoms. The Moco cofactors are the active sites of the enzyme, where oxidation occurs. The [2Fe-2S…