Selenium deficiency (Keshan disease) manifests as cardiomyopathy. Selenium is essential because it is incorporated as selenocysteine in which critical antioxidant enzyme?

• A Superoxide dismutase (MnSOD)
• B Catalase
• C Glutathione peroxidase (GPx) ✓
• D Thioredoxin reductase only

Explanation

Selenium is incorporated as selenocysteine (the 21st amino acid, encoded by UGA codon read as selenocysteine in the presence of SECIS element) in the active site of glutathione peroxidase (GPx). GPx reduces H2O2 and organic hydroperoxides (including lipid peroxides) using reduced glutathione (GSH), producing glutathione disulfide (GSSG) and water/alcohol. In selenium deficiency, GPx activity falls, allowing accumulation of reactive oxygen species and lipid peroxides, damaging cardiac mitochondria and explaining cardiomyopathy. Selenium is also incorporated into thioredoxin reductase and selenoprotein P, but GPx is the primary antioxidant selenoprotein. MnSOD uses manganese; catalase uses iron heme.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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