Comparison between xanthine oxidases from buttermilk and microorganisms regarding their ability to generate reactive oxygen species

Xanthine oxidase (XO) forms uric acid from xanthine. It is assumed that at the same time oxygen is reduced by the XO to reactive oxygen species (ROS), mainly to .O-2(-) and to H2O2. Under certain conditions such ROS can be hi ghly damaging to cellular structures. Therefore, XO was frequently used as a model system, in which the impact of ROS on cellular compounds and struct ures has been investigated. In this in vitro study xanthine oxidases from b uttermilk and from microorganisms were compared regarding their ability to generate ROS. It could be shown that both enzymes are able to transform xan thine to uric acid but differ significantly in their reductive properties t o oxygen. XO from buttermilk reduces oxygen to both .O-2(.) and H2O2 wherea s XO from microorganisms generates H2O2, but fails to form .O-2(-). Since . O-2(-) are involved in maintaining transition metal-mediated formation of h ydroxyl radicals (.OH) from H2O2, we conclude that XO from microorganisms i s therefore largely unsuitable in studies investigating just the interactio n of .O-2(-) with other ROS on cellular compounds.