Cytosolic xanthine dehydrogenase (XDH) in its oxidase form catalyzes the reaction of xanthine with H2O and oxygen to form urate and H2O2. The active form of the enzyme is a dimer (Saksela and Raivio 1996; Yamaguchi et al. 2007). The enzyme is said to occur predominantly in its dehydrogenase form, catalyzing the reaction of xanthine with NAD+ to form urate and to be converted to the oxidase form annotated here in response to stress (Ichida et al. 2012).