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The structure of cytochrome b5 reductase, the enzyme that converts methemoglobin to hemoglobin. [1]Methemoglobin (British: methaemoglobin, shortened MetHb) (pronounced "met-hemoglobin") is a hemoglobin in the form of metalloprotein, in which the iron in the heme group is in the Fe 3+ state, not the Fe 2+ of normal hemoglobin.
The congenital form of methemoglobinemia has an autosomal recessive pattern of inheritance. Due to a deficiency of the enzyme diaphorase I (cytochrome b5 reductase), methemoglobin levels rise and the blood of met-Hb patients has reduced oxygen-carrying capacity. Instead of being red in color, the arterial blood of met-Hb patients is brown.
Methemoglobin is an oxidized form of hemoglobin attached to a ferric-state iron (Fe3+), which can therefore not carry and deliver oxygen to tissues. [15] The formation of methemoglobin occurs when electrons are not returned to the iron of a normal state hemoglobin, which is not preferred for a functioning organism.
Methemoglobin is also formed in small quantities when the dissociation of oxyhemoglobin results in the formation of methemoglobin and superoxide, O 2 −, instead of the usual products. Superoxide is a free radical and causes biochemical damage, but is neutralised by the action of the enzyme superoxide dismutase.
Carboxyhemoglobin is often mistaken for the compound formed by the combination of carbon dioxide and hemoglobin, which is actually carbaminohemoglobin. Carboxyhemoglobin terminology emerged when carbon monoxide was known by its historic name, "carbonic oxide", and evolved through Germanic and British English etymological influences; the ...
Methemoglobinemia is a condition caused by elevated levels of methemoglobin in the blood. Methaemoglobin is a form of hemoglobin that contains the ferric [Fe 3+] form of iron, instead of the ferrous [Fe 2+] form . Methemoglobin cannot bind oxygen, which means it cannot carry oxygen to tissues.
Heinz bodies are formed by damage to the hemoglobin component molecules, usually through oxidative damage by administered drugs, or from an inherited mutation (i.e. change of an internal amino acid residue).
A hemichrome (FeIII) is a form of low-spin methemoglobin (metHb). Hemichromes, which precede the denaturation processes of hemoglobin (Hb), are mainly produced by partially denaturated hemoglobins and form histidine complexes.