Aldehyde oxidase/xanthine dehydrogenase <p>This entry includes aldehyde oxidases and xanthine dehydrogenases. They are both molybdenum cofactor (Moco) containing enzymes [<cite idref="PUB00043467"/>]. Aldehyde oxicases catalyse the reaction: <reaction> aldehyde + H(2)O + O(2) = a carboxylic acid + H2O2 </reaction> It binds 2 2Fe-2S clusters uses FAD and molybdopterin as cofactors. Xanthine has the same co-factors and can be converted from the dehydrogenase form (D) to the oxidase form (O). This can be done irreversibly by proteolysis or reversibly through the oxidation of sulphydryl groups. This enzyme catalyses three reactions: <reaction> Xanthine + H2O + NAD+= urate + NADH</reaction><reaction>Hypoxanthine + H2O + NAD+= xanthine + NADH</reaction><reaction>Xanthine + H2O + O2 = urate + H2O2</reaction>In <taxon tax_id="3702">Arabidopsis thaliana</taxon>, the molybdenum cofactor sulphurase ABA3 is needed for post-translational activation of aldehyde oxidase and xanthine dehydrogenase. It does this by transferring a sulphfur atom to the desulpho-molybdenum cofactor of these enzymes [<cite idref="PUB00043468"/>, <cite idref="PUB00043467"/>]</p>