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Methemoglobin (English: methaemoglobin) (pronounced "met-hemoglobin") is a form of the oxygen-carrying metalloprotein hemoglobin, in which the iron in the heme group is in the Fe3+ (ferric) state, not the Fe2+ (ferrous) of normal hemoglobin. Methemoglobin cannot bind oxygen, unlike oxyhemoglobin.〔http://www.rtso.ca/methemoglobin-causes-effects/〕 It is bluish chocolate-brown in color. In human blood a trace amount of methemoglobin is normally produced spontaneously, but when present in excess the blood becomes abnormally dark bluish brown. The NADH-dependent enzyme methemoglobin reductase (diaphorase I) is responsible for converting methemoglobin back to hemoglobin. Normally one to two percent of a person's hemoglobin is methemoglobin; a higher percentage than this can be genetic or caused by exposure to various chemicals and depending on the level can cause health problems known as methemoglobinemia. A higher level of methemoglobin will tend to cause a pulse oximeter to read closer to 85% regardless of the true level of oxygen saturation. == Common causes of elevated methemoglobin == * Reduced cellular defense mechanisms * * Children younger than 4 months exposed to various environmental agents * * Pregnant women are considered vulnerable to exposure of high levels of nitrates in drinking water * * Cytochrome b5 reductase deficiency * * G6PD deficiency * * Hemoglobin M disease * * Pyruvate kinase deficiency * Various pharmaceutical compounds * * Local anesthetic agents, especially prilocaine and benzocaine.〔http://www.fda.gov/Drugs/DrugSafety/ucm250024.htm〕 * * Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides * Environmental agents * * Aromatic amines (e.g. ''p''-nitroaniline, (patient case )) * * Arsine * * Chlorobenzene * * Chromates * * Nitrates/nitrites * Inherited disorders * * Some family members of the Fughate family in Kentucky, due to a recessive gene, had blue skin from an excess of methemoglobin.〔http://abcnews.go.com/Health/blue-skinned-people-kentucky-reveal-todays-genetic-lesson/story?id=15759819#.T2oS0HqV2So〕 * In cats * *Ingestion of Paracetamol (i.e. acetaminophen, tylenol) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「methemoglobin」の詳細全文を読む スポンサード リンク
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