Nitric oxide synthase in macrophages generates nitric oxide (NO•) as part of antimicrobial defence. When NO• combines with the superoxide radical (O2•−), which highly reactive nitrogen species is formed?
- A Peroxynitrite (ONOO−) ✓
- B Nitrous oxide
- C Hydroxyl radical (OH•)
- D Nitrogen dioxide anion
Correct answer: A. Peroxynitrite (ONOO−)
Explanation
NO• reacts with superoxide at a near diffusion-limited rate to form peroxynitrite (ONOO−), a reactive nitrogen species that nitrates tyrosine residues on proteins (nitrotyrosine is its footprint) and damages DNA and membranes. The hydroxyl radical distractor arises from hydrogen peroxide via the Fenton reaction, not from NO chemistry, so it cannot be the direct product of NO plus superoxide.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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