Question:
All of the following are involved in generating free oxygen radicals for the killing of bacteria except:
All of the following are involved in generating free oxygen radicals for the killing of bacteria except:
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Find the antioxidant enzyme that mops up peroxide rather than making radicals.
Updated On: Jun 24, 2026
- Superoxide dismutase
- Fenton reaction
- NADPH oxidase
- Glutathione peroxidase
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The Correct Option is D
Solution and Explanation
Step 1: Understand the oxidative (respiratory) burst. When neutrophils and macrophages phagocytose bacteria, they generate reactive oxygen species (ROS) inside the phagolysosome to kill the organism.
Step 2: NADPH oxidase is the trigger enzyme. It converts molecular oxygen to superoxide anion (\(O_2^-\)), the first ROS of the burst, so it is directly involved in generating free radicals.
Step 3: Superoxide dismutase converts superoxide to hydrogen peroxide (\(H_2O_2\)), and the Fenton reaction converts \(H_2O_2\) in the presence of \(Fe^{2+}\) into the highly reactive hydroxyl radical (\(OH^-\)). Both feed the radical-generating cascade.
Step 4: Glutathione peroxidase does the opposite. It is an antioxidant enzyme that detoxifies \(H_2O_2\) to water using reduced glutathione, thereby removing ROS rather than generating them.
Step 5: Therefore the exception is glutathione peroxidase, option D.
Step 2: NADPH oxidase is the trigger enzyme. It converts molecular oxygen to superoxide anion (\(O_2^-\)), the first ROS of the burst, so it is directly involved in generating free radicals.
Step 3: Superoxide dismutase converts superoxide to hydrogen peroxide (\(H_2O_2\)), and the Fenton reaction converts \(H_2O_2\) in the presence of \(Fe^{2+}\) into the highly reactive hydroxyl radical (\(OH^-\)). Both feed the radical-generating cascade.
Step 4: Glutathione peroxidase does the opposite. It is an antioxidant enzyme that detoxifies \(H_2O_2\) to water using reduced glutathione, thereby removing ROS rather than generating them.
Step 5: Therefore the exception is glutathione peroxidase, option D.
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