[NCB5R_HUMAN] Defects in CYB5R3 are the cause of methemoglobinemia CYB5R3-related (METHB-CYB5R3) [MIM:250800]. A form of methemoglobinemia, a hematologic disease characterized by the presence of excessive amounts of methemoglobin in blood cells, resulting in decreased oxygen carrying capacity of the blood, cyanosis and hypoxia. There are two types of methemoglobinemia CYB5R3-related. In type 1, the defect affects the soluble form of the enzyme, is restricted to red blood cells, and causes well-tolerated methemoglobinemia. In type 2, the defect affects both the soluble and microsomal forms of the enzyme and is thus generalized, affecting red cells, leukocytes and all body tissues. Type 2 methemoglobinemia is associated with mental deficiency and other neurologic symptoms.
[NCB5R_HUMAN] Desaturation and elongation of fatty acids, cholesterol biosynthesis, drug metabolism, and, in erythrocyte, methemoglobin reduction.
Erythrocyte NADH-cytochrome b(5) reductase reduces methaemoglobin to functional haemoglobin. In order to examine the function of the enzyme, the structure of NADH-cytochrome b(5) reductase from human erythrocytes has been determined and refined by X-ray crystallography. At 1.75 A resolution, the root-mean-square deviations (r.m.s.d.) from standard bond lengths and angles are 0.006 A and 1.03 degrees , respectively. The molecular structure was compared with those of rat NADH-cytochrome b(5) reductase and corn nitrate reductase. The human reductase resembles the rat reductase in overall structure as well as in many side chains. Nevertheless, there is a large main-chain shift from the human reductase to the rat reductase or the corn reductase caused by a single-residue replacement from proline to threonine. A model of the complex between cytochrome b(5) and the human reductase has been built and compared with that of the haem-containing domain of the nitrate reductase molecule. The interaction between cytochrome b(5) and the human reductase differs from that of the nitrate reductase because of differences in the amino-acid sequences. The structures around 15 mutation sites of the human reductase have been examined for the influence of residue substitutions using the program ROTAMER. Five mutations in the FAD-binding domain seem to be related to cytochrome b(5).
Structure of human erythrocyte NADH-cytochrome b5 reductase.,Bando S, Takano T, Yubisui T, Shirabe K, Takeshita M, Nakagawa A Acta Crystallogr D Biol Crystallogr. 2004 Nov;60(Pt 11):1929-34. Epub 2004, Oct 20. PMID:15502298
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
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↑ Percy MJ, Gillespie MJ, Savage G, Hughes AE, McMullin MF, Lappin TR. Familial idiopathic methemoglobinemia revisited: original cases reveal 2 novel mutations in NADH-cytochrome b5 reductase. Blood. 2002 Nov 15;100(10):3447-9. Epub 2002 Jul 5. PMID:12393396 doi:10.1182/blood-2002-05-1405
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↑ Bando S, Takano T, Yubisui T, Shirabe K, Takeshita M, Nakagawa A. Structure of human erythrocyte NADH-cytochrome b5 reductase. Acta Crystallogr D Biol Crystallogr. 2004 Nov;60(Pt 11):1929-34. Epub 2004, Oct 20. PMID:15502298 doi:10.1107/S0907444904020645