11. Xanthine dehydrogenase can be converted to xanthine oxidase by reversible sulfhydryl oxidation or by irreversible proteolytic modification. 12. Enzymes that contain the molybdopterin cofactor include xanthine oxidase , DMSO reductase, sulfite oxidase, and nitrate reductase. 13. Xanthine oxidase loses its function and gains ascorbase function when some of the iron atoms in XO are replaced with copper atoms.14. Type I xanthinuria has been traced directly to mutations of the " XDH " gene which mediates xanthine oxidase activity. 15. Both xanthine oxidase and xanthine oxidoreductase are also present in corneal epithelium and endothelium and may be involved in oxidative eye injury. 16. Models for hemerythrin, an enzyme with a diiron active site, and xanthine oxidase , a molybdoenzyme, have been examined. 17. In a 24-hour urine excretion of more than 800 mg, which indicates overproduction, a xanthine oxidase inhibitor is preferred. 18. Hypoxanthine is then oxidatively catabolized first to xanthine and then to uric acid, and the reaction is catalyzed by the enzyme xanthine oxidase : 19. A 24-hour urine excretion of more than 800 mg, which indicates overproduction, is an indication for a xanthine oxidase inhibitor. 20. Because xanthine oxidase is a metabolic pathway for uric acid formation, the xanthine oxidase inhibitor allopurinol is used in the treatment of gout.
