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A brownish-red form of hemoglobin that occurs when hemoglobin is oxidized either during decomposition of the blood or by the action of various oxidizing drugs or toxic agents. It contains iron in the ferric state and cannot function as an oxygen carrier.

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Biochemistry) the US spelling of methaemoglobin
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(mɛtˈhi məˌgloʊ bɪn, -ˈhɛm ə-, -ˌhi məˈgloʊ-, -ˌhɛm ə-)

a form of hemoglobin in which iron has been oxidized, resulting in brownish blood that transports less oxygen.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
There is another methemoglobin reductase system in erythrocytes that uses NADPH as a cofactor.
Methemoglobinemia: Monitor methemoglobin levels in patients with cardiopulmonary disease, hemoglobinopathy, or methemoglobin reductase deficiency Agranulocytosis: Monitor CBC count 4-10 wk after initiation of therapy; stop therapy when WBC count < 4000/[mm.sup.3] Peripheral neuropathy: Periodic neurologic screening examination by dermatologist; any suspected abnormality needs referral for full neurologic examination and electromyogram with nerve conduction studies Psychosis: Manifested by insomnia, irritation, excitability, and even violence; reversible on stopping dapsone CBC count, Complete blood cell count; Hb, hemoglobin; WBC count, white blood cell count, G6PD Glucose-6-phosphate dehydrogenase.
This is achieved predominantly through reduction of methemoglobin in an NADH-dependent manner by an enzyme called methemoglobin reductase (also known as NADH-cytochrome b5 reductase).
Newborn organisms are very sensitive to methemoglobinemia because they have an immature "methemoglobin reductase system" [5].
Production of superoxide anion is increased in congenital methemoglobinemia and methemoglobin reductase deficiency as well as acquired methemoglobinemia, e.g.
I would like to add to this well written article that we have also reported acquired methemoglobinemia cases with administration of cytanest in puerperal women with G6PD deficiency and infants in whom erythrocyte cytochrome 65 reductase was assoyed (1-4), which is the main enzyme for methemoglobin reductase in erythrocytes as mentioned by the authors.
Ferric ([Fe.sup.3+]) iron is reduced to the ferrous ([Fe.sup.2+]) state again through reductase-mediated electron transfer involving electrons contributed by NADH (reduced diphosphopyridine nucleotide) and cytochrome b5 reductase (methemoglobin reductase), which reduces the methemoglobin (8,10,11).