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. Author manuscript; available in PMC: 2012 Dec 1.
Published in final edited form as: Future Oncol. 2012 Feb;8(2):145–150. doi: 10.2217/fon.11.147

Figure 1. Recycling of methemoglobin to hemoglobin.

Figure 1

Normal erythrocyte Hgb carries oxygen in a reversible association with reduced or ferrous iron (Fe2+). Oxygenated Fe2+ Hgb oxidizes to Fe3+ MetHgb and superoxide at a rate of approximately 3% per day. (A) In the presence of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP), 3-AP interacts with the Fe2+ of Hgb in order to form 3-AP-Fe3+, which, in effect, creates MetHgb. (B) MetHgb may be reduced to Hgb by a combination of cytochrome b5 reductase and cytochrome b5. (C) The MetHgb antidote, methylene blue, can also facilitate this reaction. Hgb: Hemoglobin; MetHgb: Methemoglobin.