Superoxide dismutase (SOD) catalyses dismutation of superoxide radicals. The mitochondrial isoform of SOD (MnSOD) requires which metal cofactor, and what product is formed?
- A Manganese; forms hydrogen peroxide and oxygen ✓
- B Copper/Zinc; forms hydrogen peroxide and oxygen
- C Iron; forms hydroxyl radical and oxygen
- D Selenium; forms water and oxygen
Explanation
MnSOD (SOD2) is the mitochondrial matrix isoform containing manganese as its redox-active metal cofactor. It catalyses: 2O2•− + 2H+ → H2O2 + O2. The cytosolic/extracellular isoform Cu/Zn-SOD (SOD1) contains copper and zinc. Both isoforms produce H2O2, which is subsequently detoxified by catalase or glutathione peroxidase. Iron-SOD exists in bacteria but not in mammals. Selenium is the cofactor of glutathione peroxidase (GPx), which reduces H2O2 and lipid peroxides using reduced glutathione. Fenton reaction with iron generates hydroxyl radicals from H2O2 but this is not enzymatic dismutation.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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