-!- Acts on a variety of purines and aldehydes, including hypoxanthine. -!- The mammalian enzyme can also convert all-trans retinol to all-trans- retinoate, while the substrate is bound to a retinoid-binding protein. -!- The enzyme from eukaryotes contains [2Fe-2S], FAD and a molybdenum center. -!- The mammallian enzyme predominantly exists as the NAD-dependent dehydrogenase (EC 1.17.1.4). -!- During purification the enzyme is largely converted to an O(2)- dependent form, EC 1.17.3.2. -!- The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds (which can be catalyzed by EC 1.8.4.7 in the presence of glutathione disulfide) or limited proteolysis, which results in irreversible conversion. -!- The conversion can also occur in vivo. -!- Formerly EC 1.2.1.37 and EC 1.1.1.204.

-!- Also oxidizes hypoxanthine, some other purines and pterins, and aldehydes, but is distinct from EC 1.2.3.1. -!- Under some conditions the product is mainly superoxide rather than peroxide: R-H + H(2)O + 2 O(2) = ROH + 2 O(2)(.-) + 2 H(+). -!- The mammallian enzyme predominantly exists as an NAD-dependent dehydrogenase (EC 1.17.1.4). -!- During purification the enzyme is largely converted to the O(2)- dependent xanthine oxidase form (EC 1.17.3.2). -!- The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds (which can be catalyzed by EC 1.8.4.7 in the presence of glutathione disulfide) or limited proteolysis, which results in irreversible conversion. -!- The conversion can also occur in vivo. -!- Formerly EC 1.1.3.22 and EC 1.2.3.2.