Q. 70 The enzyme responsible for generation of hypochlorous ions during phagocytosis is
(A) NADPH oxidase
(B) catalase
(C) myeloperoxidase
(D) superoxide dismutase
Myeloperoxidase: The Key Enzyme Generating Hypochlorous Ions in Phagocytosis
During phagocytosis, neutrophils produce hypochlorous ions (HOCl) as potent antimicrobial agents, with myeloperoxidase serving as the primary enzyme responsible.
Correct Answer
(C) myeloperoxidase
Myeloperoxidase (MPO) catalyzes the reaction of hydrogen peroxide (H₂O₂) with chloride ions (Cl⁻) to form hypochlorous acid (HOCl), a critical microbicidal oxidant in phagosomes.
Role in Phagocytosis
Phagocytosis by neutrophils involves engulfing pathogens into phagosomes, where a respiratory burst generates reactive oxygen species (ROS). NADPH oxidase first produces superoxide (O₂⁻), which dismutates to H₂O₂. MPO then uses this H₂O₂ to generate HOCl via the reaction: H₂O₂ + Cl⁻ → HOCl + H₂O, enabling effective pathogen killing.
Explanation of Options
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(A) NADPH oxidase: Generates superoxide (O₂⁻) during the respiratory burst, fueling downstream ROS production but not directly forming HOCl.
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(B) Catalase: Decomposes H₂O₂ into water and oxygen, protecting cells from oxidative damage rather than generating HOCl.
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(C) Myeloperoxidase: Correct; directly produces HOCl from H₂O₂ and Cl⁻, a hallmark of neutrophil antimicrobial activity.
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(D) Superoxide dismutase: Converts superoxide to H₂O₂, an intermediate step, but does not produce HOCl.
