What pathway maintains Hgb in a reduced state?

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Multiple Choice

What pathway maintains Hgb in a reduced state?

The key idea is how hemoglobin stays in the functional ferrous state by actively reducing methemoglobin back to hemoglobin. Red blood cells use a specific enzyme system, methemoglobin reductase (cytochrome b5 reductase), which accepts electrons from NADH and donates them to methemoglobin, converting Fe3+ back to Fe2+. This direct NADH-dependent reduction keeps hemoglobin ready to bind oxygen. Other pathways play different roles. The Embden-Meyerhof pathway is glycolysis, mainly providing ATP and general NADH; it doesn’t specifically reduce methemoglobin. The Luebering-Rapoport pathway diverts from glycolysis to form 2,3-BPG, which shifts hemoglobin’s oxygen affinity rather than its redox state. The hexose monophosphate shunt (pentose phosphate pathway) generates NADPH to help keep glutathione reduced and protect cells from oxidative damage, but it does not directly reduce methemoglobin.

The key idea is how hemoglobin stays in the functional ferrous state by actively reducing methemoglobin back to hemoglobin. Red blood cells use a specific enzyme system, methemoglobin reductase (cytochrome b5 reductase), which accepts electrons from NADH and donates them to methemoglobin, converting Fe3+ back to Fe2+. This direct NADH-dependent reduction keeps hemoglobin ready to bind oxygen.

Other pathways play different roles. The Embden-Meyerhof pathway is glycolysis, mainly providing ATP and general NADH; it doesn’t specifically reduce methemoglobin. The Luebering-Rapoport pathway diverts from glycolysis to form 2,3-BPG, which shifts hemoglobin’s oxygen affinity rather than its redox state. The hexose monophosphate shunt (pentose phosphate pathway) generates NADPH to help keep glutathione reduced and protect cells from oxidative damage, but it does not directly reduce methemoglobin.

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