During ischemia-reperfusion injury, which enzyme activated by calcium influx converts xanthine dehydrogenase (XDH) to xanthine oxidase (XO), producing superoxide?
- A Caspase-3 (executioner caspase)
- B Phospholipase C (IP3-mediated)
- C Calcineurin (serine/threonine phosphatase)
- D Calpain (calcium-activated protease) ✓
Explanation
During ischemia, cytosolic calcium rises and activates calpain, a calcium-dependent cysteine protease that cleaves and converts xanthine dehydrogenase to xanthine oxidase. On reperfusion, XO uses molecular oxygen to oxidise hypoxanthine (accumulated during ischemia) to xanthine and uric acid, generating superoxide radical (O2•−) and hydrogen peroxide, initiating oxidative injury. Caspase-3 mediates apoptotic execution. Phospholipase C generates IP3 to release ER calcium but does not directly modify XDH. Calcineurin dephosphorylates NFAT and is a separate calcium target.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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