Reperfusion injury after myocardial ischaemia is primarily mediated by reactive oxygen species. The enzyme responsible for the burst of superoxide generation immediately upon reperfusion is:

• A NADPH oxidase, activated by Ca2+ influx after reperfusion
• B Mitochondrial Complex III, which reverses electron flow upon reperfusion
• C Nitric oxide synthase, generating NO that reacts with superoxide to form peroxynitrite
• D Xanthine oxidase, which converts accumulated hypoxanthine using the newly delivered O2 ✓

Explanation

During ischaemia, ATP is degraded to AMP → adenosine → inosine → hypoxanthine, which accumulates; simultaneously, xanthine dehydrogenase (XDH) is converted to xanthine oxidase (XO) by proteases/oxidation. Upon reperfusion with O2, XO rapidly oxidises accumulated hypoxanthine to xanthine and then to uric acid, generating superoxide in two successive steps. This initial burst of superoxide triggers hydroxyl radical formation and oxidative tissue injury.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.