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OXY HEMOGLOBIN (90% RELATIVE HUMIDITY)
Structural highlights
DiseaseHBA_HUMAN Defects in HBA1 may be a cause of Heinz body anemias (HEIBAN) [MIM:140700. This is a form of non-spherocytic hemolytic anemia of Dacie type 1. After splenectomy, which has little benefit, basophilic inclusions called Heinz bodies are demonstrable in the erythrocytes. Before splenectomy, diffuse or punctate basophilia may be evident. Most of these cases are probably instances of hemoglobinopathy. The hemoglobin demonstrates heat lability. Heinz bodies are observed also with the Ivemark syndrome (asplenia with cardiovascular anomalies) and with glutathione peroxidase deficiency.[1] Defects in HBA1 are the cause of alpha-thalassemia (A-THAL) [MIM:604131. The thalassemias are the most common monogenic diseases and occur mostly in Mediterranean and Southeast Asian populations. The hallmark of alpha-thalassemia is an imbalance in globin-chain production in the adult HbA molecule. The level of alpha chain production can range from none to very nearly normal levels. Deletion of both copies of each of the two alpha-globin genes causes alpha(0)-thalassemia, also known as homozygous alpha thalassemia. Due to the complete absence of alpha chains, the predominant fetal hemoglobin is a tetramer of gamma-chains (Bart hemoglobin) that has essentially no oxygen carrying capacity. This causes oxygen starvation in the fetal tissues leading to prenatal lethality or early neonatal death. The loss of three alpha genes results in high levels of a tetramer of four beta chains (hemoglobin H), causing a severe and life-threatening anemia known as hemoglobin H disease. Untreated, most patients die in childhood or early adolescence. The loss of two alpha genes results in mild alpha-thalassemia, also known as heterozygous alpha-thalassemia. Affected individuals have small red cells and a mild anemia (microcytosis). If three of the four alpha-globin genes are functional, individuals are completely asymptomatic. Some rare forms of alpha-thalassemia are due to point mutations (non-deletional alpha-thalassemia). The thalassemic phenotype is due to unstable globin alpha chains that are rapidly catabolized prior to formation of the alpha-beta heterotetramers. Note=Alpha(0)-thalassemia is associated with non-immune hydrops fetalis, a generalized edema of the fetus with fluid accumulation in the body cavities due to non-immune causes. Non-immune hydrops fetalis is not a diagnosis in itself but a symptom, a feature of many genetic disorders, and the end-stage of a wide variety of disorders. Defects in HBA1 are the cause of hemoglobin H disease (HBH) [MIM:613978. HBH is a form of alpha-thalassemia due to the loss of three alpha genes. This results in high levels of a tetramer of four beta chains (hemoglobin H), causing a severe and life-threatening anemia. Untreated, most patients die in childhood or early adolescence.[2] FunctionHBA_HUMAN Involved in oxygen transport from the lung to the various peripheral tissues. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedHigh-salt crystals of human oxy- and deoxyhaemoglobin have been studied at different levels of environmental humidity and solvent content. The structure of the oxy form remains relatively unchanged at all levels. The deoxy form, however, undergoes a water-mediated transformation when the relative humidity around the crystals is reduced below 93%. The space group is maintained during the transformation, but the unit-cell volume nearly doubles, with two tetrameric molecules in the asymmetric unit of the low-humidity form compared with one in the native crystals. Interestingly, the haem geometry in the low-humidity form is closer to that in the oxy form than to that in the native deoxy form. The quaternary structure of one of the tetramers moves slightly towards that in the oxy form, while that in the other is more different from the oxy form than that in the high-salt native deoxy form. Thus, it would appear that, as in the case of the liganded form, the deoxy form of haemoglobin can also access an ensemble of related T states. Structures of human oxy- and deoxyhaemoglobin at different levels of humidity: variability in the T state.,Biswal BK, Vijayan M Acta Crystallogr D Biol Crystallogr. 2002 Jul;58(Pt 7):1155-61. Epub 2002, Jun 20. PMID:12077435[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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