Allopurinol is used to treat hyperuricemia by inhibiting xanthine oxidase. During the oxidation of xanthine to uric acid, xanthine oxidase generates reactive oxygen species as a byproduct. Which metal cofactor is present at the active site of xanthine oxidase, and what ROS is produced during its catalytic cycle?
- A Molybdenum (as molybdopterin cofactor); superoxide and hydrogen peroxide ✓
- B Copper; hydroxyl radical
- C Zinc; singlet oxygen
- D Manganese; hypochlorous acid
Correct answer: A. Molybdenum (as molybdopterin cofactor); superoxide and hydrogen peroxide
Explanation
Xanthine oxidase is a molybdenum-containing flavoprotein with molybdopterin, FAD, and iron-sulfur clusters. It generates superoxide and H2O2 during purine oxidation. Copper is the cofactor for SOD and ceruloplasmin. Zinc is found in alcohol dehydrogenase and carbonic anhydrase. Manganese is the cofactor for mitochondrial SOD.
Reference: Lehninger Principles of Biochemistry, 7th ed.
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