## Superoxide Dismutase (SOD) Mechanism **Key Point:** SOD catalyzes the dismutation of superoxide anion (O₂⁻•) into hydrogen peroxide (H₂O₂) and molecular oxygen (O₂). This is the primary antioxidant defense against superoxide, the most abundant free radical in cells. ### Reaction Catalyzed by SOD $$2 \text{O}_2^{-\bullet} + 2\text{H}^+ \rightarrow \text{H}_2\text{O}_2 + \text{O}_2$$ **High-Yield:** SOD exists in three isoforms: - **SOD1 (Cu/Zn-SOD):** cytoplasm and nucleus - **SOD2 (Mn-SOD):** mitochondrial matrix - **SOD3 (EC-SOD):** extracellular space ### Downstream Processing The H₂O₂ produced by SOD is then neutralized by: - **Catalase** (in peroxisomes) → converts H₂O₂ to H₂O and O₂ - **Glutathione peroxidase** (cytoplasm and mitochondria) → converts H₂O₂ to H₂O using reduced glutathione (GSH) **Clinical Pearl:** Deficiency of SOD (especially SOD2) impairs mitochondrial antioxidant defense and is associated with increased oxidative stress in neurodegenerative diseases and aging. **Mnemonic:** SOD = "**S**uper **O**xide **D**ismutase" — it dismutes (breaks apart) superoxide into less harmful products. 
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