Mechanism of Release of Ferritin Iron In Vivo by Xanthine Oxidase1

Studies of the biochemical mechanism for the release of iron from hepatic ferritin stores have revealed the participation of the enzyme xanthine oxidase (1). During this reaction between the enzyme and ferritin iron some of the iron in the ferric state is reduced to the ferrous form and can be removed from the protein in the presence of iron-binding agents such as cr,a'-dipyridyl or the plasma iron-binding globulin, siderophilin. Evidence for the participation of this enzyme in the release of ferritin iron is based for the most part on in vitro studies using rat liver slices subjected to lowered oxygen tension. Such tissue slices accumulate ferrous-ferritin and high levels of hypoxanthine and xanthine, substrates for xanthine oxidase, as well as uric acid, their oxidation product. In addition, indirect evidence implicates this mechanism in the release of ferritin iron to the plasma in the intact animal; as a result of liver hypoxia following extensive blood loss, the plasma iron and uric acid of dogs is found to increase to a considerable extent. (2). The results of the present study serve to confirm the participation of xanthine oxidase in the in tivo liberation of tissue iron to the circulation.