A 5-year-old boy presents with recurrent severe bacterial infections. A nitroblue tetrazolium (NBT) test is negative. The defect is in the enzyme that initiates the respiratory burst in neutrophils. Which free radical is the first to be generated by this defective enzyme?
- A Superoxide ✓
- B Hydroxyl radical
- C Hydrogen peroxide
- D Hypochlorous acid
Correct answer: A. Superoxide
Explanation
Chronic granulomatous disease results from a defect in NADPH oxidase, the enzyme that initiates the respiratory burst. This enzyme directly generates superoxide (O2•−) from molecular oxygen. Hydrogen peroxide, hydroxyl radical, and hypochlorous acid are downstream products of superoxide dismutation and myeloperoxidase action.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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