 Here is a diagram highlighting the pathways catalyzed by xanthine oxidase.It is suggested that xanthine oxidoreductase, along with other enzymes, partecipates in the conversion of nitrate to nitrite in mammalian tissues.The protein is large, having a molecular weight of 270 kDa, and has 2 flavin molecules (bound as FAD), 2 molybdenum atoms, and 8 iron atoms bound per enzymatic unit.