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08.03.05 (3 years ago)
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from Dorland
a stands for alpha, b stands for beta, g stands for gamma, d for delta, A for hemoglobin A, F for hemoglobin F, e for epsilon, z for zeta
Hemoglobin: the red oxygen-carrying pigment of erythrocytes, formed by developing erythrocytes in bone marrow. It is a type of hemoprotein that contains four heme groups and globin and has the property of reversible oxygenation. A molecule of hemoglobin contains four polypeptide globin chains, composed of between 141 and 146 amino acids; those most often found are a and b chains, with g and d chains seen somewhat less often. Different types of hemoglobins are determined by different combinations of chains, with the number of chains of each type in the molecule being indicated by a subscript. For example, hemoglobin F (fetal h.), the predominant type in the newborn, may be written a2A g2F., and hemoglobin A (adult h.), which is normally predominant in the adult, may be written a2A b2A or a2 b2. Another hemoglobin, hemoglobin A2 (designated a2A d2A2 or a2A d2), is usually present in limited minor concentrations. Hundreds of hemoglobins with differing electrophoretic mobilities and characteristics have been reported; the first ones were given capital letters, such as S, C, D, E, G, H, I, J, K, L, M, N, and Q. As refined biochemical techniques led to the discovery of many additional hemoglobins, newer standards for nomenclature were devised: those with electrophoretic mobility equal to one of the lettered hemoglobins could be named with that letter using the place of discovery as a subscript, such as hemoglobin MSaskatoon or hemoglobin MMilwaukee. New hemoglobins with unique electrophoretic mobilities are now often named simply for the laboratory, hospital, or town where they were discovered, such as hemoglobin Chesapeake or hemoglobin Gun Hill. When known, the number of each amino acid substituting in each polypeptide in the molecule should be indicated by the appropriate superscript numeral. Symbol Hb.
hemoglobin A, normal adult hemoglobin, composed of two a and two b chains, a2Ab2A.
hemoglobin A1c, a type of glycated hemoglobin A, having a hexose attached to the N terminal of its b chain; its levels are increased in poorly controlled diabetics.
hemoglobin A2, a2Ad2, a type of normal adult hemoglobin present in small amounts, in which d chains replace the b chains.
hemoglobin anti-Lepore, an abnormal crossover hemoglobin similar to hemoglobin Lepore but whose non-a chains have fusion in the opposite configuration from those of hemoglobin Lepore (b chain portions at the N terminus and d chain portions at the C terminus); most individuals with this hemnoglobin have predominantly normal hemoglobin and do not suffer from anemia or thalassemia.
hemoglobin Bart's, an abnormal hemoglobin composed of four g chains having high oxygen affinity, seen in Southeast Asians and a few other groups; infants born with only this type of hemoglobin have hydrops fetalis and usually die within a few hours. Hemoglobin Bart's is often found mixed with hemoglobin H, resulting in a-thalassemia.
hemoglobin C, a common abnormal hemoglobin in which lysine replaces glutamic acid at position six of the b chains; it was one of the earliest hemoglobins to have its molecular abnormality defined. The homozygous state manifests as the anemic condition called hemoglobin C disease, and the asymptomatic heterozygous state is called hemoglobin C trait.
hemoglobin Chesapeake, an abnormal hemoglobin in which leucine is substituted for arginine in the a chain, resulting in high oxygen affinity so that the individual has polycythemia.
hemoglobin Constant Spring, an abnormal hemoglobin seen in Southeast Asians, characterized by 31 extra amino acid residues at the C terminus of the a chain, resulting in a form of a-thalassemia.
crossover hemoglobin, an abnormal hemoglobin that has a globin chain formed from parts of two chains that have undergone crossover, such as hemoglobin Lepore, h. anti-Lepore, and h. Kenya.
hemoglobin D, any of several abnormal hemoglobins, all characterized by electrophoretic mobility equal to that of hemoglobin S on paper or cellulose acetate but unequal on acid agar gel. The most common one is h. D Los Angeles (also known as h. D Punjab
), which has glycine substituted for glutamic acid at position 121 of the b chain. In the homozygous state, hemoglobin D manifests as the anemic state called hemoglobin D disease; the heterozygous state is clinically silent.
deoxygenated hemoglobin, deoxyhemoglobin.
hemoglobin E, an abnormal hemoglobin with lysine substituted for glutamic acid at position 26 of the b chain, seen most often in Southeast Asia, especially Thailand. The homozygous state may be asymptomatic or may be manifested as the anemic state called hemoglobin E disease, while the heterozygous state is clinically silent.
hemoglobin F, fetal h.
fast hemoglobins, those with greater mobility on electrophoresis (in an alkaline buffer) than normal hemoglobin A, such as hemoglobin K, J, or N.
fetal hemoglobin, the hemoglobin normally comprising more than half of that in the fetus, composed of two alpha and two gamma polypeptides (a2Ag2F); it has higher affinity for oxygen under physiologic conditions than does hemoglobin A. It is present in minimal amounts in adulthood and is abnormally elevated in aplastic anemia, leukemia, and certain types of thalassemia. Called also h. F.
hemoglobin G, any of various abnormal hemoglobins with an amino acid substitution on the a chain; the most common one is h. G Philadelphia, which causes a-thalassemia.
glycated hemoglobin, glycosylated hemoglobin, any of various hemoglobins to which glucose is bound by glycation; the most common one is hemoglobin A1c.
Gower hemoglobin, hemoglobin Gower, a normal hemoglobin present in early embryonic life and disappearing before birth; it occasionally consists entirely of epsilon chains (e4), but the usual forms are h. Gower-1, consisting of two zeta and two epsilon chains (z2e2) and h. Gower-2, consisting of two alpha and two epsilon chains (a2e2).
hemoglobin Gun Hill, an unstable hemoglobin with a segmental deletion of amino acids in the b chain that causes inability to bind heme and mild hemolytic anemia.
hemoglobin H, a rapidly migrating abnormal hemoglobin composed of four b chains, having a high oxygen affinity, found mainly in Southeast Asians, natives of the Mediterranean region, and a few other ethnic groups. Infants may be born with a mixture of hemoglobin H and hemoglobin Bart's. See hemoglobin H disease, under disease.
hemoglobin I, an abnormal hemoglobin resulting from an amino acid substitution in the a chain, causing a-thalassemia.
hemoglobin Kansas, an abnormal hemoglobin with threonine substituted for asparagine at position 102 of the b chain, resulting in decreased oxygen affinity and cyanosis.
hemoglobin Kenya, an abnormal type of crossover hemoglobin in which the non-a chain has a g chain portion at the N terminus and a b chain portion at the C terminus, resulting in b-thalassemia.
hemoglobin Köln, an unstable hemoglobin that has methionine substituted for valine at position 95 of the b chain, usually resulting in Heinz body anemia.
hemoglobin Lepore, any of several abnormal crossover hemoglobins having two normal a chains and two globin chains that have portions of a d chain at the N terminus and portions of a b chain at the C terminus. Homozygous individuals have about 90 per cent hemoglobin F, 10 per cent hemoglobin Lepore, and no Hemoglobin A or A2, which results in thalassemia major; heterozygotes have varying amounts of hemoglobin Lepore and hemoglobin A and may have mild anemia.
hemoglobin M, any of several abnormal hemoglobins having amino acid substitutions in the a or b chains and all associated with methemoglobinemia.
mean corpuscular hemoglobin, (MCh
) the average hemoglobin content of an erythrocyte, conventionally expressed in picograms per red cell, obtained by multiplying the blood hemoglobin concentration (in g/dL) by ten and dividing by the red cell count (in millions per mL): MCh
= Hb/RBC.
muscle hemoglobin, myoglobin.
oxidized hemoglobin, oxygenated hemoglobin, oxyhemoglobin.
hemoglobin Portland, a normal hemoglobin present in the fetus late in the first trimester of pregnancy, consisting of zeta and gamma chains (z2g2); it disappears in utero.
hemoglobin Rainier, an abnormal hemoglobin in which histidine replaces tyrosine at position 145 in the b chain; it has increased oxygen affinity and is associated with polycythemia.
reduced hemoglobin, deoxyhemoglobin.
hemoglobin S, the most common abnormal hemoglobin, having valine substituted for glutamic acid at position six of the b chain; the homozygous state results in sickle cell anemia, and the asymptomatic heterozygous state is called sickle cell trait. The delineation of the abnormality in molecular structure was a milestone in biochemical genetics, paving the way for other investigations demonstrating how substitutions of a single amino acid could produce significant clinical effects.
hemoglobin Seattle, an abnormal hemoglobin in which glutamic acid is substituted for alanine at position 76 of the b chain; it has decreased oxygen affinity.
slow hemoglobins, those less mobile on electrophoresis (in an alkaline buffer) than normal hemoglobin A, such as hemoglobin S or D.
unstable hemoglobins, abnormal hemoglobins whose molecule is unstable, usually owing to substitution or deletion of at least one amino acid. Many have increased oxygen affinity and some have Heinz bodies; affected individuals often have Heinz body anemia or some other type of hemolytic anemia.
hemoglobin Yakima, an abnormal hemoglobin in which histidine is substituted for aspartic acid at position 99 of the b chain; it has increased oxygen affinity and is associated with polycythemia.
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