Following restoration of blood flow after prolonged intestinal ischaemia, tissue injury paradoxically worsens. Which enzyme, upregulated during the ischaemic period through calcium-dependent proteolytic conversion of xanthine dehydrogenase, generates the burst of superoxide radicals seen on reperfusion?
- A NADPH oxidase
- B Myeloperoxidase
- C Xanthine oxidase ✓
- D Cytochrome P450 reductase
Correct answer: C. Xanthine oxidase
Explanation
During ischaemia, ATP degradation raises hypoxanthine levels and calcium influx converts xanthine dehydrogenase to xanthine oxidase. On reperfusion, oxygen returns and xanthine oxidase oxidises hypoxanthine to uric acid while generating large amounts of superoxide, driving reperfusion injury. NADPH oxidase and myeloperoxidase generate radicals in phagocytes during inflammation, not in this ischaemia-reperfusion sequence.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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