Superoxide dismutase (SOD) catalyses the reaction: 2O2•− + 2H+ → H2O2 + O2. The H2O2 produced must be further detoxified. Which enzyme and cofactor pair achieves this reduction to water in the mitochondrial matrix?

• A Catalase using NADH as electron donor
• B Glutathione reductase using NADPH to generate reduced glutathione
• C Glutathione peroxidase using reduced glutathione (GSH) ✓
• D Thioredoxin reductase using FAD directly

Explanation

In the mitochondrial matrix, H2O2 produced by MnSOD is detoxified by mitochondrial glutathione peroxidase (GPx1), which oxidises 2 GSH to GSSG while reducing H2O2 to 2H2O. GSSG is regenerated to GSH by glutathione reductase using NADPH, which is supplied by the TCA cycle isocitrate dehydrogenase (NADP+-dependent) and the nicotinamide nucleotide transhydrogenase. Catalase is predominantly in peroxisomes and the cytosol, not mitochondria, and does not use NADH for its catalytic cycle (it uses heme iron). Glutathione reductase regenerates GSH but does not directly reduce H2O2.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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