hemoglobin

ヘモグロビン

　 　

WordNet

1. a hemoprotein composed of globin and heme that gives red blood cells their characteristic color; function primarily to transport oxygen from the lungs to the body tissues; "fish have simpler hemoglobin than mammals" (同)haemoglobin, Hb

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1. ヘモグロビン,血色素
2. hemoglobin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/09/10 06:16:42」(JST)

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hemoglobin (heterotetramer, (αβ)2)
Structure of human hemoglobin. The proteins' α and β subunits are in red and blue, and the iron-containing heme groups in green. From PDB 1GZX Proteopedia Hemoglobin
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Protein type		metalloprotein, globulin
Function		oxygen-transport
Cofactor(s)		heme (4)
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Subunit Name	Gene	Chromosomal Locus
Hb-α1	HBA1	Chr. 16 p13.3
Hb-α2	HBA2	Chr. 16 p13.3
Hb-β	HBB	Chr. 11 p15.5

Hemoglobin (/ˈhiːməˌɡloʊbɪn/); also spelled haemoglobin and abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates (with the exception of the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the rest of the body (i.e. the tissues) where it releases the oxygen to burn nutrients to provide energy to power the functions of the organism in the process called metabolism.

In mammals, the protein makes up about 96% of the red blood cells' dry content (by weight), and around 35% of the total content (including water). Hemoglobin has an oxygen-binding capacity of 1.34 mL O₂ per gram of hemoglobin, which increases the total blood oxygen capacity seventy-fold compared to dissolved oxygen in blood. The mammalian hemoglobin molecule can bind (carry) up to four oxygen molecules.

Hemoglobin is involved in the transport of other gases: It carries some of the body's respiratory carbon dioxide (about 10% of the total) as carbaminohemoglobin, in which CO₂ is bound to the globin protein. The molecule also carries the important regulatory molecule nitric oxide bound to a globin protein thiol group, releasing it at the same time as oxygen.

Hemoglobin is also found outside red blood cells and their progenitor lines. Other cells that contain hemoglobin include the A9 dopaminergic neurons in the substantia nigra, macrophages, alveolar cells, and mesangial cells in the kidney. In these tissues, hemoglobin has a non-oxygen-carrying function as an antioxidant and a regulator of iron metabolism.

Hemoglobin and hemoglobin-like molecules are also found in many invertebrates, fungi, and plants. In these organisms, hemoglobins may carry oxygen, or they may act to transport and regulate other things such as carbon dioxide, nitric oxide, hydrogen sulfide and sulfide. A variant of the molecule, called leghemoglobin, is used to scavenge oxygen away from anaerobic systems, such as the nitrogen-fixing nodules of leguminous plants, before the oxygen can poison the system.

Research history

Max Perutz, one of the founding fathers of molecular biology

In 1825 J.F. Engelhard discovered that the ratio of Fe to protein is identical in the hemoglobins of several species. From the known atomic mass of iron he calculated the molecular mass of hemoglobin to n × 16000 (n = number of irons per hemoglobin, now known to be 4), the first determination of a protein's molecular mass. This "hasty conclusion" drew a lot of ridicule at the time from scientists who could not believe that any molecule could be that big. Gilbert Smithson Adair confirmed Engelhard's results in 1925 by measuring the osmotic pressure of hemoglobin solutions.

The oxygen-carrying protein hemoglobin was discovered by Hünefeld in 1840. In 1851, German physiologist Otto Funke published a series of articles in which he described growing hemoglobin crystals by successively diluting red blood cells with a solvent such as pure water, alcohol or ether, followed by slow evaporation of the solvent from the resulting protein solution. Hemoglobin's reversible oxygenation was described a few years later by Felix Hoppe-Seyler.

In 1959, Max Perutz determined the molecular structure of myoglobin (similar to hemoglobin) by X-ray crystallography. This work resulted in his sharing with John Kendrew the 1962 Nobel Prize in Chemistry.

The role of hemoglobin in the blood was elucidated by French physiologist Claude Bernard. The name hemoglobin is derived from the words heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme group. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces. The most common type of hemoglobin in mammals contains four such subunits.

Genetics

Hemoglobin consists mostly of protein subunits (the "globin" molecules), and these proteins, in turn, are folded chains of a large number of different amino acids called polypeptides. The amino acid sequence of any polypeptide created by a cell is in turn determined by the stretches of DNA called genes. In all proteins, it is the amino acid sequence that determines the protein's chemical properties and function.

There is more than one hemoglobin gene. The amino acid sequences of the globin proteins in hemoglobins usually differ between species. These differences grow with evolutionary distance between species. For example, the most common hemoglobin sequences in humans and chimpanzees are nearly identical, differing by only one amino acid in both the alpha and the beta globin protein chains. These differences grow larger between less closely related species.

Even within a species, different variants of hemoglobin always exist, although one sequence is usually a "most common" one in each species. Mutations in the genes for the hemoglobin protein in a species result in hemoglobin variants. Many of these mutant forms of hemoglobin cause no disease. Some of these mutant forms of hemoglobin, however, cause a group of hereditary diseases termed the hemoglobinopathies. The best known hemoglobinopathy is sickle-cell disease, which was the first human disease whose mechanism was understood at the molecular level. A (mostly) separate set of diseases called thalassemias involves underproduction of normal and sometimes abnormal hemoglobins, through problems and mutations in globin gene regulation. All these diseases produce anemia.

Protein alignment of human hemoglobin proteins, alpha, beta, and delta subunits respectively. The alignments were created using Uniprot's alignment tool available online.

Variations in hemoglobin amino acid sequences, as with other proteins, may be adaptive. For example, recent studies have suggested genetic variants in deer mice that help explain how deer mice that live in the mountains are able to survive in the thin air that accompanies high altitudes. A researcher from the University of Nebraska-Lincoln found mutations in four different genes that can account for differences between deer mice that live in lowland prairies versus the mountains. After examining wild mice captured from both highlands and lowlands, it was found that: the genes of the two breeds are "virtually identical–except for those that govern the oxygen-carrying capacity of their hemoglobin". "The genetic difference enables highland mice to make more efficient use of their oxygen", since less is available at higher altitudes, such as those in the mountains. Mammoth hemoglobin featured mutations that allowed for oxygen delivery at lower temperatures, thus enabling mammoths to migrate to higher latitudes during the Pleistocene.

Synthesis

Hemoglobin (Hb) is synthesized in a complex series of steps. The heme part is synthesized in a series of steps in the mitochondria and the cytosol of immature red blood cells, while the globin protein parts are synthesized by ribosomes in the cytosol. Production of Hb continues in the cell throughout its early development from the proerythroblast to the reticulocyte in the bone marrow. At this point, the nucleus is lost in mammalian red blood cells, but not in birds and many other species. Even after the loss of the nucleus in mammals, residual ribosomal RNA allows further synthesis of Hb until the reticulocyte loses its RNA soon after entering the vasculature (this hemoglobin-synthetic RNA in fact gives the reticulocyte its reticulated appearance and name).

Structure

Heme b group

Hemoglobin has a quaternary structure characteristic of many multi-subunit globular proteins. Most of the amino acids in hemoglobin form alpha helices, connected by short non-helical segments. Hydrogen bonds stabilize the helical sections inside this protein, causing attractions within the molecule, folding each polypeptide chain into a specific shape. Hemoglobin's quaternary structure comes from its four subunits in roughly a tetrahedral arrangement.

In most vertebrates, the hemoglobin molecule is an assembly of four globular protein subunits. Each subunit is composed of a protein chain tightly associated with a non-protein heme group. Each protein chain arranges into a set of alpha-helix structural segments connected together in a globin fold arrangement, so called because this arrangement is the same folding motif used in other heme/globin proteins such as myoglobin. This folding pattern contains a pocket that strongly binds the heme group.

A heme group consists of an iron (Fe) ion (charged atom) held in a heterocyclic ring, known as a porphyrin. This porphyrin ring consists of four pyrrole molecules cyclically linked together (by methine bridges) with the iron ion bound in the center. The iron ion, which is the site of oxygen binding, coordinates with the four nitrogens in the center of the ring, which all lie in one plane. The iron is bound strongly (covalently) to the globular protein via the imidazole ring of F8 histidine residue (also known as the proximal histidine) below the porphyrin ring. A sixth position can reversibly bind oxygen by a coordinate covalent bond, completing the octahedral group of six ligands. Oxygen binds in an "end-on bent" geometry where one oxygen atom binds Fe and the other protrudes at an angle. When oxygen is not bound, a very weakly bonded water molecule fills the site, forming a distorted octahedron.

Even though carbon dioxide is carried by hemoglobin, it does not compete with oxygen for the iron-binding positions but is bound to the protein chains of the structure.

The iron ion may be either in the Fe²⁺ or in the Fe³⁺ state, but ferrihemoglobin (methemoglobin) (Fe³⁺) cannot bind oxygen. In binding, oxygen temporarily and reversibly oxidizes (Fe²⁺) to (Fe³⁺) while oxygen temporarily turns into superoxide, thus iron must exist in the +2 oxidation state to bind oxygen. If superoxide ion associated to Fe³⁺ is protonated, the hemoglobin iron will remain oxidized and incapable of binding oxygen. In such cases, the enzyme methemoglobin reductase will be able to eventually reactivate methemoglobin by reducing the iron center.

In adult humans, the most common hemoglobin type is a tetramer (which contains 4 subunit proteins) called hemoglobin A, consisting of two α and two β subunits non-covalently bound, each made of 141 and 146 amino acid residues, respectively. This is denoted as α₂β₂. The subunits are structurally similar and about the same size. Each subunit has a molecular weight of about 16,000 daltons, for a total molecular weight of the tetramer of about 64,000 daltons (64,458 g/mol). Thus, 1 g/dL = 0.01551 mmol/L. Hemoglobin A is the most intensively studied of the hemoglobin molecules.

In human infants, the hemoglobin molecule is made up of 2 α chains and 2 γ chains. The gamma chains are gradually replaced by β chains as the infant grows.

The four polypeptide chains are bound to each other by salt bridges, hydrogen bonds, and the hydrophobic effect.

Oxygen saturation

In general, hemoglobin can be saturated with oxygen molecules (oxyhemoglobin), or desaturated with oxygen molecules (deoxyhemoglobin).

Oxyhemoglobin

Oxyhemoglobin is formed during physiological respiration when oxygen binds to the heme component of the protein hemoglobin in red blood cells. This process occurs in the pulmonary capillaries adjacent to the alveoli of the lungs. The oxygen then travels through the blood stream to be dropped off at cells where it is utilized as a terminal electron acceptor in the production of ATP by the process of oxidative phosphorylation. It does not, however, help to counteract a decrease in blood pH. Ventilation, or breathing, may reverse this condition by removal of carbon dioxide, thus causing a shift up in pH.

Hemoglobin exists in two forms, a taut (tense) form (T) and a relaxed form (R). Various factors such as low pH, high CO₂ and high 2,3 BPG at the level of the tissues favor the taut form, which has low oxygen affinity and releases oxygen in the tissues. Conversely, a high pH, low CO₂, or low 2,3 BPG favors the relaxed form, which can better bind oxygen. The partial pressure of the system also affects O₂ affinity where, at high partial pressures of oxygen (such as those present in the alveoli), the relaxed (high affinity, R) state is favoured. Inversely, at low partial pressures (such as those present in respiring tissues), the (low affinity, T) tense state is favoured. Additionally, the binding of oxygen to the Iron-II heme pulls the iron into the plane of the porphyrin ring, causing a slight conformational shift. The shift encourages oxygen to bind to the three remaining hemes within hemoglobin (thus, oxygen binding is cooperative).

Deoxygenated hemoglobin

Deoxygenated hemoglobin is the form of hemoglobin without the bound oxygen. The absorption spectra of oxyhemoglobin and deoxyhemoglobin differ. The oxyhemoglobin has significantly lower absorption of the 660 nm wavelength than deoxyhemoglobin, while at 940 nm its absorption is slightly higher. This difference is used for measurement of the amount of oxygen in patient's blood by an instrument called pulse oximeter. This difference also accounts for the presentation of cyanosis, the blue to purplish color that tissues develop during hypoxia.

Iron's oxidation state in oxyhemoglobin

Assigning oxygenated hemoglobin's oxidation state is difficult because oxyhemoglobin (Hb-O₂), by experimental measurement, is diamagnetic (no net unpaired electrons), yet the low-energy electron configurations in both oxygen and iron are paramagnetic (suggesting at least one unpaired electron in the complex). The lowest-energy form of oxygen, and the lowest energy forms of the relevant oxidation states of iron, are these:

• Triplet oxygen, the lowest-energy molecular oxygen species, has two unpaired electrons in antibonding π* molecular orbitals.
• Iron(II) tends to exist in a high-spin configuration where unpaired electrons exist in E_g antibonding orbitals.
• Iron(III) has an odd number of electrons, and thus must have one or more unpaired electrons, in any energy state.

All of these structures are paramagnetic (have unpaired electrons), not diamagnetic. Thus, a non-intuitive (e.g., a higher-energy for at least one species) distribution of electrons in the combination of iron and oxygen must exist, in order to explain the observed diamagnetism and no unpaired electrons.

The three logical possibilities to produce diamagnetic (no net spin) Hb-O₂ are:

1. Low-spin Fe²⁺ binds to singlet oxygen. Both low-spin iron and singlet oxygen are diamagnetic. However, the singlet form of oxygen is the higher-energy form of the molecule.
2. Low-spin Fe³⁺ binds to .O₂^- (the superoxide ion) and the two unpaired electrons couple antiferromagnetically, giving diamagnetic properties.
3. Low-spin Fe⁴⁺ binds to peroxide, O₂^2-. Both are diamagnetic.

Direct experimental data:

• X-ray photoelectron spectroscopy suggests iron has an oxidation state of approximately 3.2
• Infrared vibrational frequencies of the O-O bond suggests a bond length fitting with superoxide (a bond order of about 1.6, with superoxide being 1.5).
• X-ray Absorption Near Edge Structures at the iron K-edge. The energy shift of 5 eV between Deoxyhemoglobin and Oxyhemoglobin, as for all the Methemoglobin species, strongly suggests an actual local charge closer to Fe³⁺ than Fe²⁺.

Thus, the nearest formal oxidation state of iron in Hb-O₂ is the +3 state, with oxygen in the −1 state (as superoxide .O₂^-). The diamagnetism in this configuration arises from the single unpaired electron on superoxide aligning antiferromagnetically from the single unpaired electron on iron, to give no net spin to the entire configuration, in accordance with diamagnetic oxyhemoglobin from experiment.

The second choice of the three logical possibilities above for diamagnetic oxyhemoglobin being found correct by experiment, is not surprising: singlet oxygen (possibility #1) and large separations of charge (possibility #3) are both unfavorably high-energy states. Iron's shift to a higher oxidation state in Hb-O₂ decreases the atom's size, and allows it into the plane of the porphyrin ring, pulling on the coordinated histidine residue and initiating the allosteric changes seen in the globulins.

Early postulates by bio-inorganic chemists claimed that possibility #1 (above) was correct and that iron should exist in oxidation state II. This conclusion seemed likely, since the iron oxidation state III as methemoglobin, when not accompanied by superoxide .O₂^- to "hold" the oxidation electron, was known to render hemoglobin incapable of binding normal triplet O₂ as it occurs in the air. It was thus assumed that iron remained as Fe(II) when oxygen gas was bound in the lungs. The iron chemistry in this previous classical model was elegant, but the required presence of the required diamagnetic high-energy singlet oxygen was never explained. It was classically argued that the binding of an oxygen molecule placed high-spin iron(II) in an octahedral field of strong-field ligands; this change in field would increase the crystal field splitting energy, causing iron's electrons to pair into the low-spin configuration, which would be diamagnetic in Fe(II). This forced low-spin pairing is indeed thought to happen in iron when oxygen binds, but is not enough to explain iron's change in size. Extraction of an additional electron from iron by oxygen is required to explain both iron's smaller size and observed increased oxidation state, and oxygen's weaker bond.

The assignment of a whole-number oxidation state is a formalism, as the covalent bonds are not required to have perfect bond orders involving whole electron transfer. Thus, all three models for paramagnetic Hb-O₂ may contribute to some small degree (by resonance) to the actual electronic configuration of Hb-O₂. However, the model of iron in Hb-O₂ being Fe(III) is more correct than the classical idea that it remains Fe(II).

Cooperativity

A schematic visual model of oxygen-binding process, showing all four monomers and hemes, and protein chains only as diagramatic coils, to facilitate visualization into the molecule. Oxygen is not shown in this model, but, for each of the iron atoms, it binds to the iron (red sphere) in the flat heme. For example, in the upper-left of the four hemes shown, oxygen binds at the left of the iron atom shown in the upper-left of diagram. This causes the iron atom to move backward into the heme that holds it (the iron moves upward as it binds oxygen, in this illustration), tugging the histidine residue (modeled as a red pentagon on the right of the iron) closer, as it does. This, in turn, pulls on the protein chain holding the histidine.

When oxygen binds to the iron complex, it causes the iron atom to move back toward the center of the plane of the porphyrin ring (see moving diagram). At the same time, the imidazole side-chain of the histidine residue interacting at the other pole of the iron is pulled toward the porphyrin ring. This interaction forces the plane of the ring sideways toward the outside of the tetramer, and also induces a strain in the protein helix containing the histidine as it moves nearer to the iron atom. This strain is transmitted to the remaining three monomers in the tetramer, where it induces a similar conformational change in the other heme sites such that binding of oxygen to these sites becomes easier.

In the tetrameric form of normal adult hemoglobin, the binding of oxygen is, thus, a cooperative process. The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule, with the first oxygens bound influencing the shape of the binding sites for the next oxygens, in a way favorable for binding. This positive cooperative binding is achieved through steric conformational changes of the hemoglobin protein complex as discussed above; i.e., when one subunit protein in hemoglobin becomes oxygenated, a conformational or structural change in the whole complex is initiated, causing the other subunits to gain an increased affinity for oxygen. As a consequence, the oxygen binding curve of hemoglobin is sigmoidal, or S-shaped, as opposed to the normal hyperbolic curve associated with noncooperative binding.

The dynamic mechanism of the cooperativity in hemoglobin and its relation with the low-frequency resonance has been discussed.

Binding for ligands other than oxygen

Besides the oxygen ligand, which binds to hemoglobin in a cooperative manner, hemoglobin ligands also include competitive inhibitors such as carbon monoxide (CO) and allosteric ligands such as carbon dioxide (CO₂) and nitric oxide (NO). The carbon dioxide is bound to amino groups of the globin proteins as carbaminohemoglobin, and is thought to account for about 10% of carbon dioxide transport in mammals. Nitric oxide is bound to specific thiol groups in the globin protein to form an S-nitrosothiol, which dissociates into free nitric oxide and thiol again, as the hemoglobin releases oxygen from its heme site. This nitric oxide transport to peripheral tissues is hypothesized to assist oxygen transport in tissues, by releasing vasodilatory nitric oxide to tissues in which oxygen levels are low.

Competitive

The binding of oxygen is affected by molecules such as carbon monoxide (CO) (for example, from tobacco smoking, car exhaust, and incomplete combustion in furnaces). CO competes with oxygen at the heme binding site. Hemoglobin binding affinity for CO is 250 times greater than its affinity for oxygen, meaning that small amounts of CO dramatically reduce hemoglobin's ability to transport oxygen. Since carbon monoxide is a colorless, odorless and tasteless gas, and poses a potentially fatal threat, detectors have become commercially available to warn of dangerous levels in residences. When hemoglobin combines with CO, it forms a very bright red compound called carboxyhemoglobin, which may cause the skin of CO poisoning victims to appear pink in death, instead of white or blue. When inspired air contains CO levels as low as 0.02%, headache and nausea occur; if the CO concentration is increased to 0.1%, unconsciousness will follow. In heavy smokers, up to 20% of the oxygen-active sites can be blocked by CO.

In similar fashion, hemoglobin also has competitive binding affinity for cyanide (CN⁻), sulfur monoxide (SO), nitric oxide (NO), and sulfide (S²⁻), including hydrogen sulfide (H₂S). All of these bind to iron in heme without changing its oxidation state, but they nevertheless inhibit oxygen-binding, causing grave toxicity.

The iron atom in the heme group must initially be in the ferrous (Fe²⁺) oxidation state to support oxygen and other gases' binding and transport (it temporarily switches to ferric during the time oxygen is bound, as explained above). Initial oxidation to the ferric (Fe³⁺) state without oxygen converts hemoglobin into "hemiglobin" or methemoglobin (pronounced "MET-hemoglobin"), which cannot bind oxygen. Hemoglobin in normal red blood cells is protected by a reduction system to keep this from happening. Nitric oxide is capable of converting a small fraction of hemoglobin to methemoglobin in red blood cells. The latter reaction is a remnant activity of the more ancient nitric oxide dioxygenase function of globins.

Allosteric

Further information: Oxygen-hemoglobin dissociation curve

Carbon dioxide occupies a different binding site on the hemoglobin. Carbon dioxide is more readily dissolved in deoxygenated blood, facilitating its removal from the body after the oxygen has been released to tissues undergoing metabolism. This increased affinity for carbon dioxide by the venous blood is known as the Haldane effect. Through the enzyme carbonic anhydrase, carbon dioxide reacts with water to give carbonic acid, which decomposes into bicarbonate and protons:

CO₂ + H₂O → H₂CO₃ → HCO₃^- + H⁺

The sigmoidal shape of hemoglobin's oxygen-dissociation curve results from cooperative binding of oxygen to hemoglobin.

Hence, blood with high carbon dioxide levels is also lower in pH (more acidic). Hemoglobin can bind protons and carbon dioxide, which causes a conformational change in the protein and facilitates the release of oxygen. Protons bind at various places on the protein, while carbon dioxide binds at the α-amino group. Carbon dioxide binds to hemoglobin and forms carbaminohemoglobin. This decrease in hemoglobin's affinity for oxygen by the binding of carbon dioxide and acid is known as the Bohr effect (shifts the O₂-saturation curve to the right). Conversely, when the carbon dioxide levels in the blood decrease (i.e., in the lung capillaries), carbon dioxide and protons are released from hemoglobin, increasing the oxygen affinity of the protein. A reduction in the total binding capacity of hemoglobin to oxygen (i.e. shifting the curve down, not just to the right) due to reduced pH is called the root effect. This is seen in bony fish.

It is necessary for hemoglobin to release the oxygen that it binds; if not, there is no point in binding it. The sigmoidal curve of hemoglobin makes it efficient in binding (taking up O₂ in lungs), and efficient in unloading (unloading O₂ in tissues).

In people acclimated to high altitudes, the concentration of 2,3-Bisphosphoglycerate (2,3-BPG) in the blood is increased, which allows these individuals to deliver a larger amount of oxygen to tissues under conditions of lower oxygen tension. This phenomenon, where molecule Y affects the binding of molecule X to a transport molecule Z, is called a heterotropic allosteric effect.

Animals other than humans use different molecules to bind to hemoglobin and change its O₂ affinity under unfavorable conditions. Fish use both ATP and GTP. These bind to a phosphate "pocket" on the fish hemoglobin molecule, which stabilizes the tense state and therefore decreases oxygen affinity. GTP reduces hemoglobin oxygen affinity much more than ATP, which is thought to be due to an extra hydrogen bond formed that further stabilizes the tense state. Under hypoxic conditions, the concentration of both ATP and GTP is reduced in fish red blood cells to increase oxygen affinity.

A variant hemoglobin, called fetal hemoglobin (HbF, α₂γ₂), is found in the developing fetus, and binds oxygen with greater affinity than adult hemoglobin. This means that the oxygen binding curve for fetal hemoglobin is left-shifted (i.e., a higher percentage of hemoglobin has oxygen bound to it at lower oxygen tension), in comparison to that of adult hemoglobin. As a result, fetal blood in the placenta is able to take oxygen from maternal blood.

Hemoglobin also carries nitric oxide in the globin part of the molecule. This improves oxygen delivery in the periphery and contributes to the control of respiration. NO binds reversibly to a specific cysteine residue in globin; the binding depends on the state (R or T) of the hemoglobin. The resulting S-nitrosylated hemoglobin influences various NO-related activities such as the control of vascular resistance, blood pressure and respiration. NO is not released in the cytoplasm of erythrocytes but transported by an anion exchanger called AE1 out of them.

A study was performed to examine the influence of the form of hemoglobin (Hb) on the partitioning of inhaled volatile organic compounds (VOCs) into [human and animal] blood. Benzene was the prototypic VOC used in the investigations for this research due to the similar properties it shares with many other VOCs. To be specific, this study analyses the influence of the water solubility of Hb on the partitioning coefficient (PC) of a VOC as compared to the influence of the "species" or form of Hb. The different forms of blood used include: human hemoglobin (HbA), rat Hb, and sickle-cell hemoglobin (HbS). Rat Hb contains little water and is in a quasi-crystalline form, found inside the red blood cells (RBC), meaning they are more hydrophobic than human Hb, which are water-soluble. Sickle-cell hemoglobin (HbS) is water-soluble, however it can become water-insoluble, forming hydrophobic polymers, when deoxygenated. The findings state that the benzene PC for rat Hb was much higher than human that for Hb; however, the tests that measured the PCs of the oxygenated and deoxygenated forms of HbA and HbS did not differ, indicating that the affinity of benzene was not affected by the water solubility of Hb.

Types in humans

Hemoglobin variants are a part of the normal embryonic and fetal development, but may also be pathologic mutant forms of hemoglobin in a population, caused by variations in genetics. Some well-known hemoglobin variants such as sickle-cell anemia are responsible for diseases, and are considered hemoglobinopathies. Other variants cause no detectable pathology, and are thus considered non-pathological variants.

In the embryo:

• Gower 1 (ζ₂ε₂)
• Gower 2 (α₂ε₂) (PDB 1A9W)
• Hemoglobin Portland I (ζ₂γ₂)
• Hemoglobin Portland II (ζ₂β₂).

In the fetus:

• Hemoglobin F (α₂γ₂) (PDB 1FDH).

In postnatal people:

• Hemoglobin A (α₂β₂) (PDB 1BZ0) – The most common with a normal amount over 95%
• Hemoglobin A₂ (α₂δ₂) – δ chain synthesis begins late in the third trimester and, in adults, it has a normal range of 1.5–3.5%
• Hemoglobin F (α₂γ₂) – In adults Hemoglobin F is restricted to a limited population of red cells called F-cells. However, the level of Hb F can be elevated in persons with sickle-cell disease and beta-thalassemia.

Gene expression of hemoglobin before and after birth. Also identifies the types of cells and organs in which the gene expression (data on Wood W.G., (1976). Br. Med. Bull. 32, 282.)

Variant forms that cause disease:

• Hemoglobin D-Punjab – (α₂β^D₂) – A variant form of hemoglobin.

• Hemoglobin H (β₄) – A variant form of hemoglobin, formed by a tetramer of β chains, which may be present in variants of α thalassemia.
• Hemoglobin Barts (γ₄) – A variant form of hemoglobin, formed by a tetramer of γ chains, which may be present in variants of α thalassemia.
• Hemoglobin S (α₂β^S₂) – A variant form of hemoglobin found in people with sickle cell disease. There is a variation in the β-chain gene, causing a change in the properties of hemoglobin, which results in sickling of red blood cells.
• Hemoglobin C (α₂β^C₂) – Another variant due to a variation in the β-chain gene. This variant causes a mild chronic hemolytic anemia.
• Hemoglobin E (α₂β^E₂) – Another variant due to a variation in the β-chain gene. This variant causes a mild chronic hemolytic anemia.
• Hemoglobin AS – A heterozygous form causing Sickle cell trait with one adult gene and one sickle cell disease gene
• Hemoglobin SC disease – A compound heterozygous form with one sickle gene and another encoding Hemoglobin C.

Degradation in vertebrate animals

When red cells reach the end of their life due to aging or defects, they are broken down in spleen. The hemoglobin molecule is broken up, and the iron gets recycled. This process also produces one molecule of carbon monoxide for every molecule of heme degraded. Heme degradation is one of the few natural sources of carbon monoxide in the human body, and is responsible for the normal blood levels of carbon monoxide even in people breathing pure air. The other major final product of heme degradation is bilirubin. Increased levels of this chemical are detected in the blood if red cells are being destroyed more rapidly than usual. Improperly degraded hemoglobin protein or hemoglobin that has been released from the blood cells too rapidly can clog small blood vessels, especially the delicate blood filtering vessels of the kidneys, causing kidney damage. Iron is removed from heme and salvaged for later use, it is stored as hemosiderin or ferritin in tissues and transported in plasma by beta globulins as transferins. When the porphyrin ring is broken up, the fragments are normally secreted as a yellow pigment called bilirubin, which is secreted into the intestines as bile. Intestines metabolise bilirubin into urobilinogen. Urobilinogen leaves the body in faeces, in a pigment called stercobilin. Globulin is metabolised into amino acids that are then released into circulation.

Role in disease

Hemoglobin deficiency can be caused either by decreased amount of hemoglobin molecules, as in anemia, or by decreased ability of each molecule to bind oxygen at the same partial pressure of oxygen. Hemoglobinopathies (genetic defects resulting in abnormal structure of the hemoglobin molecule) may cause both. In any case, hemoglobin deficiency decreases blood oxygen-carrying capacity. Hemoglobin deficiency is, in general, strictly distinguished from hypoxemia, defined as decreased partial pressure of oxygen in blood, although both are causes of hypoxia (insufficient oxygen supply to tissues).

Other common causes of low hemoglobin include loss of blood, nutritional deficiency, bone marrow problems, chemotherapy, kidney failure, or abnormal hemoglobin (such as that of sickle-cell disease).

High hemoglobin levels may be caused by exposure to high altitudes, smoking, dehydration, or tumors.

The ability of each hemoglobin molecule to carry oxygen is normally modified by altered blood pH or CO₂, causing an altered oxygen–hemoglobin dissociation curve. However, it can also be pathologically altered in, e.g., carbon monoxide poisoning.

Decrease of hemoglobin, with or without an absolute decrease of red blood cells, leads to symptoms of anemia. Anemia has many different causes, although iron deficiency and its resultant iron deficiency anemia are the most common causes in the Western world. As absence of iron decreases heme synthesis, red blood cells in iron deficiency anemia are hypochromic (lacking the red hemoglobin pigment) and microcytic (smaller than normal). Other anemias are rarer. In hemolysis (accelerated breakdown of red blood cells), associated jaundice is caused by the hemoglobin metabolite bilirubin, and the circulating hemoglobin can cause renal failure.

Some mutations in the globin chain are associated with the hemoglobinopathies, such as sickle-cell disease and thalassemia. Other mutations, as discussed at the beginning of the article, are benign and are referred to merely as hemoglobin variants.

There is a group of genetic disorders, known as the porphyrias that are characterized by errors in metabolic pathways of heme synthesis. King George III of the United Kingdom was probably the most famous porphyria sufferer.

To a small extent, hemoglobin A slowly combines with glucose at the terminal valine (an alpha aminoacid) of each β chain. The resulting molecule is often referred to as Hb A_1c. As the concentration of glucose in the blood increases, the percentage of Hb A that turns into Hb A_1c increases. In diabetics whose glucose usually runs high, the percent Hb A_1c also runs high. Because of the slow rate of Hb A combination with glucose, the Hb A_1c percentage is representative of glucose level in the blood averaged over a longer time (the half-life of red blood cells, which is typically 50–55 days).

Glycosylated hemoglobin is the form of hemoglobin to which glucose is bound. The binding of glucose to amino acids in the hemoglobin takes place spontaneously (without the help of an enzyme) in many proteins, and is not known to serve a useful purpose. However, the binding to hemoglobin does serve as a record for average blood glucose levels over the lifetime of red cells, which is approximately 120 days. The levels of glycosylated hemoglobin are therefore measured in order to monitor the long-term control of the chronic disease of type 2 diabetes mellitus (T2DM). Poor control of T2DM results in high levels of glycosylated hemoglobin in the red blood cells. The normal reference range is approximately 4–5.9 %. Though difficult to obtain, values less than 7% are recommended for people with T2DM. Levels greater than 9% are associated with poor control of the glycosylated hemoglobin, and levels greater than 12% are associated with very poor control. Diabetics who keep their glycosylated hemoglobin levels close to 7% have a much better chance of avoiding the complications that may accompany diabetes (than those whose levels are 8% or higher). In addition, increased glycosylation of hemoglobin increases its affinity for oxygen, therefore preventing its release at the tissue and inducing a level of hypoxia in extreme cases.

Elevated levels of hemoglobin are associated with increased numbers or sizes of red blood cells, called polycythemia. This elevation may be caused by congenital heart disease, cor pulmonale, pulmonary fibrosis, too much erythropoietin, or polycythemia vera.

A recent study done in Pondicherry, India, shows its importance in coronary artery disease.

Diagnostic uses

Main article: Hemoglobinometer

A Hemoglobin concentration measurement being administered before a blood donation at the American Red Cross Boston Blood Donation Center.

Hemoglobin concentration measurement is among the most commonly performed blood tests, usually as part of a complete blood count. For example it is typically tested before or after blood donation. Results are reported in g/L, g/dL or mol/L. 1 g/dL equals about 0.6206  mmol/L, although the latter units are not used as often due to uncertainty regarding the polymeric state of the molecule. This conversion factor, using the single globin unit molecular weight of 16,000 Da, is more common for hemoglobin concentration in blood. For MCHC (mean corpuscular hemoglobin concentration) the conversion factor 0.155, which uses the tetramer weight of 64,500 Da, is more common. Normal levels are:

• Men: 13.8 to 18.0 g/dL (138 to 180 g/L, or 8.56 to 11.17 mmol/L)
• Women: 12.1 to 15.1 g/dL (121 to 151 g/L, or 7.51 to 9.37 mmol/L)
• Children: 11 to 16 g/dL (111 to 160 g/L, or 6.83 to 9.93 mmol/L)
• Pregnant women: 11 to 14 g/dL (110 to 140 g/L, or 6.83 to 8.69 mmol/L)

Normal values of hemoglobin in the 1st and 3rd trimesters of pregnant women must be at least 11 g/dL and at least 10.5 g/dL during the 2nd trimester.

Dehydration or hyperhydration can greatly influence measured hemoglobin levels. Albumin can indicate hydration status.

If the concentration is below normal, this is called anemia. Anemias are classified by the size of red blood cells, the cells that contain hemoglobin in vertebrates. The anemia is called "microcytic" if red cells are small, "macrocytic" if they are large, and "normocytic" otherwise.

Hematocrit, the proportion of blood volume occupied by red blood cells, is typically about three times the hemoglobin concentration measured in g/dL. For example, if the hemoglobin is measured at 17 g/dL, that compares with a hematocrit of 51%.

Laboratory hemoglobin test methods require a blood sample (arterial, venous, or capillary) and analysis on hematology analyzer and CO-oximeter. Additionally, a new noninvasive hemoglobin (SpHb) test method called Pulse CO-Oximetry is also available with comparable accuracy to invasive methods.

Concentrations of oxy- and deoxyhemoglobin can be measured continuously, regionally and noninvasively using NIRS. NIRS can be used both on the head as on muscles. This technique is often used for research in e.g. elite sports training, ergonomics, rehabilition, patient monitoring, neonatal research, functional brain monitoring, brain computer interface, urology (bladder contraction), neurology (Neurovascular coupling) and more.

Long-term control of blood sugar concentration can be measured by the concentration of Hb A_1c. Measuring it directly would require many samples because blood sugar levels vary widely through the day. Hb A_1c is the product of the irreversible reaction of hemoglobin A with glucose. A higher glucose concentration results in more Hb A_1c. Because the reaction is slow, the Hb A_1c proportion represents glucose level in blood averaged over the half-life of red blood cells, is typically 50–55 days. An Hb A_1c proportion of 6.0% or less show good long-term glucose control, while values above 7.0% are elevated. This test is especially useful for diabetics.

The functional magnetic resonance imaging (fMRI) machine uses the signal from deoxyhemoglobin, which is sensitive to magnetic fields since it is paramagnetic. Combined measurement with NIRS shows good correlation with both the oxy- and deoxyhemoglobin signal compared to the BOLD signal.

Analogues in non-vertebrate organisms

A variety of oxygen-transport and -binding proteins exist in organisms throughout the animal and plant kingdoms. Organisms including bacteria, protozoans, and fungi all have hemoglobin-like proteins whose known and predicted roles include the reversible binding of gaseous ligands. Since many of these proteins contain globins and the heme moiety (iron in a flat porphyrin support), they are often called hemoglobins, even if their overall tertiary structure is very different from that of vertebrate hemoglobin. In particular, the distinction of "myoglobin" and hemoglobin in lower animals is often impossible, because some of these organisms do not contain muscles. Or, they may have a recognizable separate circulatory system but not one that deals with oxygen transport (for example, many insects and other arthropods). In all these groups, heme/globin-containing molecules (even monomeric globin ones) that deal with gas-binding are referred to as oxyhemoglobins. In addition to dealing with transport and sensing of oxygen, they may also deal with NO, CO₂, sulfide compounds, and even O₂ scavenging in environments that must be anaerobic. They may even deal with detoxification of chlorinated materials in a way analogous to heme-containing P450 enzymes and peroxidases.

The giant tube worm Riftia pachyptila showing red hemoglobin-containing plumes

The structure of hemoglobins varies across species. Hemoglobin occurs in all kingdoms of organisms, but not in all organisms. Primitive species such as bacteria, protozoa, algae, and plants often have single-globin hemoglobins. Many nematode worms, molluscs, and crustaceans contain very large multisubunit molecules, much larger than those in vertebrates. In particular, chimeric hemoglobins found in fungi and giant annelids may contain both globin and other types of proteins.

One of the most striking occurrences and uses of hemoglobin in organisms is in the giant tube worm (Riftia pachyptila, also called Vestimentifera), which can reach 2.4 meters length and populates ocean volcanic vents. Instead of a digestive tract, these worms contain a population of bacteria constituting half the organism's weight. The bacteria react with H₂S from the vent and O₂ from the water to produce energy to make food from H₂O and CO₂. The worms end with a deep-red fan-like structure ("plume"), which extends into the water and absorbs H₂S and O₂ for the bacteria, and CO₂ for use as synthetic raw material similar to photosynthetic plants. The structures are bright-red due to their containing several extraordinarily complex hemoglobins that have up to 144 globin chains, each including associated heme structures. These hemoglobins are remarkable for being able to carry oxygen in the presence of sulfide, and even to carry sulfide, without being completely "poisoned" or inhibited by it as hemoglobins in most other species are.

Other oxygen-binding proteins

Myoglobin

Found in the muscle tissue of many vertebrates, including humans, it gives muscle tissue a distinct red or dark gray color. It is very similar to hemoglobin in structure and sequence, but is not a tetramer; instead, it is a monomer that lacks cooperative binding. It is used to store oxygen rather than transport it.

Hemocyanin

The second most common oxygen-transporting protein found in nature, it is found in the blood of many arthropods and molluscs. Uses copper prosthetic groups instead of iron heme groups and is blue in color when oxygenated.

Hemerythrin

Some marine invertebrates and a few species of annelid use this iron-containing non-heme protein to carry oxygen in their blood. Appears pink/violet when oxygenated, clear when not.

Chlorocruorin

Found in many annelids, it is very similar to erythrocruorin, but the heme group is significantly different in structure. Appears green when deoxygenated and red when oxygenated.

Vanabins

Also known as vanadium chromagens, they are found in the blood of sea squirts. There were once hypothesized to use the rare metal vanadium as an oxygen binding prosthetic group. However, although they do contain vanadium by preference, they apparently bind little oxygen, and thus have some other function, which has not been elucidated (sea squirts also contain some hemoglobin). They may act as toxins.

Erythrocruorin

Found in many annelids, including earthworms, it is a giant free-floating blood protein containing many dozens—possibly hundreds—of iron- and heme-bearing protein subunits bound together into a single protein complex with a molecular mass greater than 3.5 million daltons.

Pinnaglobin

Only seen in the mollusc Pinna squamosa. Brown manganese-based porphyrin protein.

Leghemoglobin

In leguminous plants, such as alfalfa or soybeans, the nitrogen fixing bacteria in the roots are protected from oxygen by this iron heme containing oxygen-binding protein. The specific enzyme protected is nitrogenase, which is unable to reduce nitrogen gas in the presence of free oxygen.

Coboglobin

A synthetic cobalt-based porphyrin. Coboprotein would appear colorless when oxygenated, but yellow when in veins.

Presence in nonerythroid cells

Some nonerythroid cells (i.e., cells other than the red blood cell line) contain hemoglobin. In the brain, these include the A9 dopaminergic neurons in the substantia nigra, astrocytes in the cerebral cortex and hippocampus, and in all mature oligodendrocytes. It has been suggested that brain hemoglobin in these cells may enable the "storage of oxygen to provide a homeostatic mechanism in anoxic conditions, which is especially important for A9 DA neurons that have an elevated metabolism with a high requirement for energy production". It has been noted further that "A9 dopaminergic neurons may be at particular risk since in addition to their high mitochondrial activity they are under intense oxidative stress caused by the production of hydrogen peroxide via autoxidation and/or monoamine oxidase (MAO)-mediated deamination of dopamine and the subsequent reaction of accessible ferrous iron to generate highly toxic hydroxyl radicals". This may explain the risk of these cells for degeneration in Parkinson's disease. The hemoglobin-derived iron in these cells is not the cause of the post-mortem darkness of these cells (origin of the Latin name, substantia nigra), but rather is due to neuromelanin.

Outside the brain, hemoglobin has non-oxygen-carrying functions as an antioxidant and a regulator of iron metabolism in macrophages, alveolar cells, and mesangial cells in the kidney.

In history, art and music

Heart of Steel (Hemoglobin) (2005) by Julian Voss-Andreae. The images show the 5-foot (1.60 m) tall sculpture right after installation, after 10 days, and after several months of exposure to the elements.

Historically, an association between the color of blood and rust occurs in the association of the planet Mars, with the Roman god of war, since the planet is an orange-red, which reminded the ancients of blood. Although the color of the planet is due to iron compounds in combination with oxygen in the Martian soil, it is a common misconception that the iron in hemoglobin and its oxides gives blood its red color. The color is actually due to the porphyrin moiety of hemoglobin to which the iron is bound, not the iron itself, although the ligation and redox state of the iron can influence the pi to pi* or n to pi* electronic transitions of the porphyrin and hence its optical characteristics.

Artist Julian Voss-Andreae created a sculpture called "Heart of Steel (Hemoglobin)" in 2005, based on the protein's backbone. The sculpture was made from glass and weathering steel. The intentional rusting of the initially shiny work of art mirrors hemoglobin's fundamental chemical reaction of oxygen binding to iron.

Rock band Placebo recorded a song called "Haemoglobin" with the lyrics "Haemoglobin is the key to a healthy heartbeat". French rap artist MC Solaar also had a successful single titled "La Concubine de l'hémoglobine" in 1994.

See also

• Vaska's complex - iridium organometallic complex notable for its ability to bind to O₂ reversibly.
• Chlorophyll
• Globin fold
• Hemocyanin
• Hemoprotein
• Sickle-cell disease
• Complete Blood Count
• Hemoglobinometer

Hemoglobin variants:

• Hb A_1C
• Hemoglobin A2
• Hemoglobin C
• Hemoglobin F

Hemoglobin protein subunits (genes):

• Alpha globin 1
• Beta globin
• Delta globin

Hemoglobin compounds:

• Carbaminohemoglobin (with carbon dioxide, colored blue)
• Carboxyhemoglobin (with carbon monoxide, colored cherry-red)
• Oxyhemoglobin (with diatomic oxygen, colored blood-red)

References

Further reading

• Campbell, MK (1999). Biochemistry (third ed.). Harcourt. ISBN 0-03-024426-9. 
• Eshaghian, S; Horwich, TB; Fonarow, GC (2006). "An unexpected inverse relationship between HbA1c levels and mortality in patients with diabetes and advanced systolic heart failure". Am Heart J 151 (1): 91. doi:10.1016/j.ahj.2005.10.008. PMID 16368297. 
• Ganong, WF (2003). Review of Medical Physiology (21st ed.). Lange. ISBN 0-07-140236-5. 
• Hager, T (1995). Force of Nature: The Life of Linus Pauling. Simon and Schuster. ISBN 0-684-80909-5. 
• Kneipp J, Balakrishnan G, Chen R, Shen TJ, Sahu SC, Ho NT, Giovannelli JL, Simplaceanu V, Ho C, Spiro T (2005). "Dynamics of allostery in hemoglobin: roles of the penultimate tyrosine H bonds". J Mol Biol 356 (2): 335–53. doi:10.1016/j.jmb.2005.11.006. PMID 16368110. 

External links

• Proteopedia Hemoglobin
• National Anemia Action Council – anemia.org
• New hemoglobin type causes mock diagnosis with pulse oxymeters
• Animation of hemoglobin: from deoxy to oxy form

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

• 1. 正常ヒトヘモグロビンの構造および機能 structure and function of normal human hemoglobins
• 2. 貧血を有する成人患者に対するアプローチ approach to the adult patient with anemia
• 3. 貧血を有する小児に対するアプローチ approach to the child with anemia
• 4. 異常ヘモグロビン症の検査室診断 laboratory diagnosis of the hemoglobinopathies
• 5. ヘモグロビン変異の概要 introduction to hemoglobin mutations

English Journal

• Impact of insulin resistance, body mass index, disease duration, and duration of metformin use on the efficacy of vildagliptin.

• Schweizer A, Dejager S, Foley JE.SourceNovartis Pharma AG, Postfach, 4002, Basel, Switzerland, anja.schweizer@novartis.com.
• Diabetes therapy : research, treatment and education of diabetes and related disorders.Diabetes Ther.2012 Nov;3(1):8. Epub 2012 Jun 27.
• INTRODUCTION: The optimal stage for dipeptidyl peptidase-4 (DPP-4) inhibitor therapy in the course of type 2 diabetes mellitus (T2DM) is still under discussion, with often a perception that treatment with these agents may be less beneficial with increasing disease progression, due to loss of beta-ce
• PMID 22736406

• Patients with Type 2 Diabetes Initiating Exenatide Twice Daily or Insulin in Clinical Practice: CHOICE Study.

• Matthaei S, Reaney M, Mathieu C, Ostenson CG, Krarup T, Guerci B, Kiljanski J, Petto H, Bruhn D, Theodorakis M.SourceDiabetes-Zentrum Quakenbrück, Fachabteilung fur Diabetologie, Stoffwechsel und Endokrinologie am Christlichen Krankenhaus, Klinisches Diabeteszentrum der DDG, Akademisches Lehrkrankenhausder Medizinischen Hochschule Hannover, Danziger Str.10, 49610, Quakenbruck, Germany, s.matthaei@ckq-gmbh.de.
• Diabetes therapy : research, treatment and education of diabetes and related disorders.Diabetes Ther.2012 Nov;3(1):6. Epub 2012 Jun 20.
• INTRODUCTION: Changes to Treatment and Outcomes in Patients with Type 2 Diabetes Initiating Injectable Therapy (CHOICE) is a European prospective, observational cohort study assessing time to, and factors associated with, a significant change in therapy after type 2 diabetes patients initiate their
• PMID 22714818

• Physician reasons for nonpharmacologic treatment of hyperglycemia in older patients newly diagnosed with type 2 diabetes mellitus.

• Marrett E, Zhang Q, Kanitscheider C, Davies MJ, Radican L, Feinglos MN.SourceGlobal Health Outcomes, WS2E85, 1 Merck Drive, Whitehouse Station, NJ, 08889, USA, elizabeth.marrett@merck.com.
• Diabetes therapy : research, treatment and education of diabetes and related disorders.Diabetes Ther.2012 Nov;3(1):5. Epub 2012 Jun 15.
• INTRODUCTION: To identify reasons why primary care physicians (PCPs) do not treat older patients newly diagnosed with type 2 diabetes mellitus (T2DM) with antihyperglycemic agents following diagnosis.METHODS: US PCPs were surveyed via the internet regarding their reasons for not treating patients ag
• PMID 22700283

Japanese Journal

• ヘモグロビン結合アッセイの改良及び乳牛の分娩後における牛ハプトグロビン濃度推移 (日本獣医師会学会学術誌) -- (産業動物臨床・家畜衛生関連部門)

• 中村 正明,小山 毅,松井 義貴 [他]
• 日本獣医師会雑誌 65(9), 682-688, 2012-09
• NAID 40019434729

• 症例報告 劇症1型糖尿病発症時のHbA1cが異常低値であることを契機に異常ヘモグロビン(Hb J-Lome)の合併が判明した1例

• 小野 恭裕,山本 匡介,大橋 昌夫 [他]
• 糖尿病 55(8), 627-631, 2012-08
• NAID 40019424471

• Preferred Pace Tapping Activates the Frontal Lobe

• Shimoda Kaori,Katsuyama Shiori,Lee Bunsuk [他]
• 北関東医学 62(3), 271-276, 2012-08
• … Oxygenated hemoglobin (oxy-Hb)concentrations (Δ［oxy-Hb］) were monitored during 30s finger-tapping with the non-dominant hand.There were two paces for finger-tapping : one pace the subject decided by themselves and the other pacegiven by metronome. …
• NAID 40019415932

Related Links

• Hemoglobin - Wikipedia, the free encyclopedia

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates (with the exception of the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in the blood carries ...

• ヘモグロビン - Wikipedia

ヘモグロビン（hemoglobin）とは、ヒトを含む全ての脊椎動物や一部のその他の動物の 血液中に存在する赤血球の中にあるタンパク質である。酸素分子と結合する性質を持ち 、肺から全身へと酸素を運搬する役割を担っている。赤色素であるヘムをもっているため ...

Related Pictures

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★リンクテーブル★

リンク元	「100Cases 34」「ヘモグロビン」「mean corpuscular hemoglobin concentration」「Hb」「blood pigment」
拡張検索	「SLS hemoglobin」「sodium lauryl sulfate hemoglobin」「hemoglobin/oxygen binding」「hemoglobin Alc」

「100Cases 34」

　　[★]

☆case34　てんかん発作

■症例

23歳　アフリカ-カリブ系　女性　銀行の店員

主訴：てんかん発作

現病歴：強直間代発作を2回起こしたところを母親が目撃していた。娘の行動は次第におかしくなり、また娘は自分のことを話している声が聞こえていた(幻聴)。最近、頭痛を訴えていた。体重が減少し、脱毛があった。盗汗と主に足と手の小関節に及ぶflitting 関節痛を訴えていた。服用薬なし。タバコ1日5-10本、アルコール10 unit/week(缶ビール(350ml)6本弱)

既往歴：特記なし(medical or psychiatric history)

家族歴：

生活歴：

・身体診断

意識：眠そうだが痛みに反応。頚部硬直：なし。頭髪：薄く斑状。体温38.5℃。リンパ節：たくさんの部位で触知。

心拍：104/分、整。血圧：164/102 mmHg。心血管系、呼吸器系、腹部：異常なし。

神経所見：focal anormalityなし(局所性異常)。乳頭浮腫：認めず。

・検査

(血液生化学)

上昇：erythrocyte sedimentation rate、urea、creatinine

低下：hemoglobin、white cell count、platelet

正常：mean corpuscular volume、sodium、potassium、glucose

(腰椎穿刺)

上昇：leukocytes、CSF protein

正常：CSF glucose

(尿検査)

蛋白：＋＋＋。血尿：＋＋＋。赤血球：＋＋。赤血球円柱：あり。

(その他)

胸部X線：異常なし。ECG：洞性頻脈。頭部CT：正常。CSFグラム染色：陰性(光顕レベルで細菌なし)

■glossary

fall out　(毛髪などが)抜ける

night sweat 盗汗、寝汗

tonic-clonic generalized seizure 全般性強直間代発作

flit　vi (鳥・蝶など)すいすい/ひらひら飛ぶ、飛び回る、飛翔する。(人が)軽やかに通る、行き交う。(時が)(飛ぶように)すぎる。(幻想など)去来する、よぎる、(表情が)かすめる

drowsy　adj. 眠い。眠そうな。眠気を誘う。ものうい。眠ったような

stiffness　n. 堅いこと、堅ぐるしさ、がんこさ

delirium tremens 振戦譫妄

hypertensive encephalopathy 高血圧性脳症

alopecia　脱毛症

African-Caribbean アフリカ-カリブ系

fit n.　(病気の)発作。引きつけ、痙攣。(感情の)激発、一時的興奮、気まぐれ

chorea n. 舞踏病

recreational drug 耽溺性があり乱用される脱法薬物

urgent adj. (物・事が)急を要する、緊急の、背拍質(pressing)。(～を)緊急に必要とする(in)。(S is ～ (with O1) for [in] O2)(人が)(O1(人)に)O2(物・事)をしつこく求める。(人に/～するように)催促する(for/to do)。(要求などが)執拗な。

□てんかん発作

・新規発生したてんかん発作の原因(ICU.805-806)

・薬物中毒(テオフィリンなど)

・薬物からの離脱(アルコールなど)

・感染症(髄膜炎、膿瘍など)

・頭部外傷

・虚血障害(虚血あるいはびまん性)

・占拠性病変(腫瘍あるいは血腫)

・代謝性障害(肝性脳症、尿毒症性脳症、敗血症、低血糖、低ナトリウム血症、低カルシウム血症など)

・合併症(ICU.805-806)

・全身性てんかん発作の場合：高血圧、乳酸アシドーシス、高体温、呼吸障害、誤嚥、肺水腫、横紋筋融解、自傷、不可逆性の神経学的障害(30分間以上てんかん発作が持続した場合)

■可能性の高い診断

　全身性エリテマトーデス systemic lupus erythematosus(SLE)

■鑑別診断のポイント

　自己免疫疾患は多彩な症状を示す。そのため、個々の症状に着目して鑑別診断をあげるのではなく、症状や検査値の異常を総合的に見て判断する必要がある。

■解答

　(第1パラグラフ)SLEの病態

精神症状：(SLEは脳で血管炎を呈することで生じる)うつ(depression)、統合失調症様の精神病、痙攣(fits)、舞踏病(chorea)、脳梗塞/脊髄梗塞

脳脊髄液：白血球増多(leukopenia)、蛋白増加

血液：自己免疫性溶血貧血(Coombs'-positive hemolytic anemia)がありうる。白血球減少と血小板減少症は普通にみられる。

腎症状：ループス腎炎は普通に見られ、顕微鏡的血尿・タンパク尿、ネフローゼ、あるいは腎不全が現れるかもしれない。

関節症状：変形を伴わない関節痛(PIP関節(近位指節間関節)、MP関節(中手指節関節)、手関節)

　(第2パラグラフ)SLEの確定診断のための検査・治療

　・すぐにすべきことは降圧薬、抗痙攣薬の投与

　・確定診断のために次の検査を行っていく(もっとも、症例の提示された所見で(日本の？)SLEの診断基準を満たすけど)

　　・検疫血清検査：抗DNA抗体、C3、C4

　　・腎生検：ループス腎炎の程度を把握

　・治療：活動性の感染がないことを確認　←　薬物療法ではステロイドや免疫抑制薬を使うため

　　・ステロイド静脈内投与、あるいはシクロホスファミドなどの細胞毒性薬(cytotoxic agents)の投与

　　・重症、治療抵抗性だったら血漿交換を行う。

■鑑別診断　頭痛/精神病的様態(psychiatric features)/痙攣

・髄膜炎、脳炎

・レクリエーショナルドラッグの中毒(例えばコカイン)

・脳腫瘍

・急性のアルコール禁断症状：振戦譫妄

・高血圧脳症

■KEYPOINT

・SLEは特に若いアフリカ系-カリブ系に普通に一般的

・SLEでは主に神経症状と精神症状をを伴って現れることがある

・白血球低下と血小板の低下はしばしばSLEを示唆する

□tonic-clonic seizure 強直間代発作

　意識消失とともに全身の随意筋に強直痙攣が生じ(強直痙攣期tonic convulsion)、次いで全身の筋の強直と弛緩とが律動的に繰り返される時期(間代痙攣期clonic convulsion)を経て、発作後もうろう状態を呈する一連の発作。

□350ml アルコール5%

350x0.05/10=1.75 unit

□細胞毒性薬

　免疫抑制薬や抗腫瘍薬として用いられる。

antimetabolites

アザチオプリン azathioprine

メトトレキセート methotrexate

ミコフェノール酸 mycophenolic acid, ミコフェノール酸モフェチル mycophenolate mofetil

レフルノミド leflunomide

alkylating agents

シクロホスファミド cyclophosphamide

「ヘモグロビン」

　　[★]

英

hemoglobin, Hb

同

血色素

関

酸素化ヘモグロビン、脱酸素化ヘモグロビン、赤血球。グロビン鎖、ヘモグロビン濃度

生化学

• 67 kDa

血液内科学

• ２種類のグロビンタンパク質が各２個集まりヘテロ４量体を形成したもの。
• 発生段階によってできるヘモグロビンが異なる
• α鎖系はζ→α
• β鎖系はε→γ→β δ

• 発生初期：ζ₂ε₂
• 胎児期　：α₂γ₂
• 乳児期　：α₂β₂(HbA), α₂δ₂(HbA₂), α₂γ₂(HbF)
• 成人

α₂β₂(HbA)　：Hbの97%

α₂δ₂(HbA₂)　：Hbの2%

α₂γ₂(HbF)　：Hbの2%

発生初期：ZE
成人　　：B > D > G , Aは共通

機能

• O₂運搬
• CO₂運搬
• 体液pHの調整

CO₂運搬

• 血液中に溶解する　：排泄されたCO2の5%(Kaplan Q book p.101)、9%(SP.655)
• ヘモグロビンのN末のアミノ基でカルバミン酸を形成して　：排出されたCO2の15%(HBC.45)、11%(SP.655)　カルバミノヘモグロビン
• 赤血球中のCAによりbicarbonateを産生し、血漿により運搬される　：排泄されたCO2のほとんど(HBC.45)、80%(SP.655)

臨床検査

• 臨床検査では、血液1dl中のヘモグロビンの量(g)を定量する。略号はHb

基準値 (ヘモグロビン濃度)

-2007前期生理学授業プリント

• 男性：14 - 18 (g/dl)　　16±2 (g/dl)
• 女性：12 - 16 (g/dl)　　14±2 (g/dl)

異常値の出るメカニズム第5版 p.79

• 男:13～19 g/dl
• 女:12～18 g/dl

HIM. A-2

• 男:13.3-16.2 g/dl
• 女:12.0-15.8 g/dl

パニック値

出典不明

• ≦5 g/dl、≧17.0 g/dl

輸液によるヘモグロビン濃度の上昇

• 予測方法(1)：予測されるヘモグロビン上昇(g/dl) = 投与ヘモグロビン量(g) / 循環血液量(dl)
• 予測方法(2)：濃厚赤血球2単位でおよそヘモグロビン上昇は1(g/dl)

国試

• 103E056

「mean corpuscular hemoglobin concentration」

　　[★]

関

hemoglobin, mean corpuscular concentration

「Hb」

　　[★] ヘモグロビン hemoglobin 　

「blood pigment」

　　[★]

• 血色素

関

hemoglobin

「SLS hemoglobin」

　　[★] ラウリル硫酸ナトリウム・ヘモグロビン

「sodium lauryl sulfate hemoglobin」

　　[★] ラウリル硫酸ナトリウム・ヘモグロビン

「hemoglobin/oxygen binding」

　　[★] ヘモグロビン-酸素間結合

「hemoglobin Alc」

　　[★]

同

glycosylated hemoglobin