Kinetic Behavior of Xanthine Oxidase and Potential Active Site Inhibitors
Xanthine oxidase (XO) is an enzyme that converts hypoxanthine to xanthine and xanthine to uric acid, the last two steps in purine metabolism. The mechanism contains reductive and oxidative half reactions and uses oxygen gas as its final electron acceptor. During ischemic conditions, the oxidative half reaction does not occur, leading to a build up of reducing equivalents. Upon reintroduction of oxygen, these reducing equivalents rapidly convert oxygen to H2O2 and O2¡¥ leading to oxidative tissue damage. Because the mechanism of XO has recently been challenged, the first goal is to solidify the kinetic behavior of this enzyme. The overall goal is to find an inhibitor, which would slow the release of electrons to oxygen. Allopurinol, a common XO inhibitor, has been shown to reduce the severity of oxidative damage following ischemia; however, this helps only in patients already on Allopurinol therapy. A fast-acting inhibitor that releases slowly and that could be administered during an ischemic episode is necessary to protect patients not currently on allopurinol therapy. Currently, we are using selected compounds to study active site binding, which will provide us with the information needed to find such an inhibitor.