oxyhemoglobin

酸素化ヘモグロビン、オキシヘモグロビン、酸化ヘモグロビン、oxyhaemoglobin 　

WordNet

1. the bright red hemoglobin that is a combination of hemoglobin and oxygen from the lungs; "oxyhemoglobin transports oxygen to the cells of the body" (同)oxyhaemoglobin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/08/23 13:19:44」(JST)

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Hemoglobin, human, adult (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 ( /hiːməˈɡloʊbɪn/; 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, and collects the resultant carbon dioxide to bring it back to the respiratory organs to be dispensed from the organism.

In mammals, the protein makes up about 97% of the red blood cells' dry content, 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

The oxygen-carrying protein hemoglobin was discovered by Hünefeld in 1840. In 1851, 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 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 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 (the "globin" chains) subunits, 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, which 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.

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). Glycine is the precursor of porphyrins.

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 methene 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 the 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 actually 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 temporally 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 17,000 daltons^{[citation needed]}, for a total molecular weight of the tetramer of about 64,000 daltons (64,458 g/mol). Thus, 1 g/dL = 0.1551 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 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.

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 stretching 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 seemed particularly 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.

It should be noted that 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).

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.

Cooperative

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 which 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.

Competitive

Hemoglobin's oxygen-binding capacity is decreased in the presence of carbon monoxide because both gases compete for the same binding sites on hemoglobin, carbon monoxide binding preferentially in place of oxygen.

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 (S^2-), 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.

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 (ζ₂γ₂)

In the fetus:

• Hemoglobin F (α₂γ₂) (PDB 1FDH)

In adults:

• 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 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 - Another 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. When the porphyrin ring is broken up, the fragments are normally secreted in the bile by the liver. This process also produces one molecule of carbon monoxide for every molecule of heme degraded. This is one of the few natural sources of carbon monoxide production 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. Heme is degraded to a yellow pigment called bilirubin. Liver secretes bilirubin 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 which are then released into circulation.

Role in disease

In sickle cell hemoglobin (HbS) glutamic acid in position 6 (in beta chain) is mutated to valine. This change allows the deoxygenated form of the hemoglobin to stick to itself.

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

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 0.1551  mmol/L. Normal levels are:

• Men: 13.8 to 18.0 g/dL (138 to 182 g/L, or 2.09 to 2.71 mmol/L)
• Women: 12.1 to 15.1 g/dL (121 to 151 g/L, or 1.86 to 2.48  mmol/L)
• Children: 11 to 16 g/dL (111 to 160 g/L, or 1.71 to 2.48 mmol/L)
• Pregnant women: 11 to 12 g/dL (110 to 120 g/L, or 1.71 to 1.86 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 cell 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 presence of iron from hemoglobin in these cells also results in the post-mortem darkness of these cells, which is the origin of the Latin name, substantia nigra.

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

The planet Mars

Historically, the color of blood was associated with rust, as ancient Romans associated the planet Mars with the god of war since Mars is orange-red. The color of Mars is due to the iron oxide in the Martian soil, but the red in blood is not due to the iron in hemoglobin and its oxides, which is a common misconception. The red is 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.

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

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'Hemoglobin" in 1994.

See also

• Proteopedia Hemoglobin
• 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 Edition). Harcourt. ISBN 0-03-024426-9 
• Eshaghian, S; Horwich, TB; Fonarow, GC (January 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 (Twenty-First Edition). 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 .

• Hardison, RC (June 11, 1996). "A brief history of hemoglobins: plant, animal, protist, and bacteria". Proc Natl Acad Sci USA 93 (12): 5675–9. doi:10.1073/pnas.93.12.5675. PMC 39118. PMID 8650150. http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=8650150 .
• Kneipp, J; Balakrishnan, G; Chen, R, Shen TJ, Sahu SC, Ho NT, Giovannelli JL, Simplaceanu V, Ho C, Spiro TG (November 22, 2005). "Dynamics of allostery in hemoglobin: roles of the penultimate tyrosine H bonds". J Mol Biol. PMID 16368110 .
• Steinberg, MH (2001). Disorders of Hemoglobin: Genetics, Pathophysiology, and Clinical Management. Cambridge University Press. ISBN 0-521-63266-8. http://books.google.com/books?vid=ISBN0521632668 .

External links

• Hemoglobin - Test, Levels and Information on MedicineNet
• Interactive hemoglobin saturation curves
• Interactive models of hemoglobin (Requires MDL Chime)
• Hemoglobin. Гемоглобин. Норма гемоглобина в крови
• National Anemia Action Council - anemia.org
• New hemoglobin type causes mock diagnosis with pulse oxymeters

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. 静脈血ガスおよび動脈血液ガスの代替 venous blood gases and other alternatives to arterial blood gases
• 2. 一酸化炭素中毒 carbon monoxide poisoning
• 3. 成人における確定診断を得られていない低血圧やショックの評価および初期アプローチ evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock
• 4. 小児における、アデノイド切除同時施行例を含む扁桃摘出に対する麻酔 anesthesia for tonsillectomy with or without adenoidectomy in children
• 5. Newborn screening for critical congenital heart disease using pulse oximetry

English Journal

• Impaired cerebral haemodynamic function associated with chronic traumatic brain injury in professional boxers.

• Bailey DM, Jones DW, Sinnott A, Brugniaux JV, New KJ, Hodson D, Marley CJ, Smirl JD, Ogoh S, Ainslie PN.SourceNeurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, Wales, UK. dbailey1@glam.ac.uk
• Clinical science (London, England : 1979).Clin Sci (Lond).2013 Feb;124(3):177-89. doi: 10.1042/CS20120259.
• The present study examined to what extent professional boxing compromises cerebral haemodynamic function and its association with CTBI (chronic traumatic brain injury). A total of 12 male professional boxers were compared with 12 age-, gender- and physical fitness-matched non-boxing controls. We ass
• PMID 22913765

• Multiscale analysis of hypoxemia in methemoglobin anemia.

• Sanyal T, Chakraborty S.SourceDepartment of Chemical Engineering, Indian Institute of Technology - Kharagpur, Kharagpur 721302, India.
• Mathematical biosciences.Math Biosci.2013 Feb;241(2):167-80. doi: 10.1016/j.mbs.2012.11.001. Epub 2012 Nov 27.
• Methemoglobinemia is a disease that results from abnormally high levels of methemoglobin (MetHb) in the red blood cell (RBC), which is caused by simultaneous uptake of oxygen (O(2)) and nitric oxide (NO) in the human lungs. MetHb is produced in the RBC by irreversible NO-induced oxidation of the oxy
• PMID 23201463

Japanese Journal

• 3P109 酸素化ヘモグロビン、ミオグロビンの酸化反応 : pH依存性と温度依存性(ヘム蛋白質,第48回日本生物物理学会年会)

• Wakasa Yuya,Iizuka Tetsutaro,Imai Kiyohiro
• 生物物理 50(SUPPLEMENT_2), S163-S164, 2010-08-15
• NAID 110008103041

• Eye Movement Performance and Prefrontal Hemodynamics during Saccadic Eye Movements in the Elderly

• FUJIWARA Katsuo,KIYOTA Naoe,KUNITA Kenji,YASUKAWA Midori,MAEDA Kaoru,DENG Xingyun
• Journal of physiological anthropology 29(2), 71-78, 2010-03-01
• … Measures included reaction times of both saccades, error rate during anti-saccade, and concentration of oxyhemoglobin (Δoxy-Hb) in the prefrontal cortex during both saccades. …
• NAID 10026191617

Related Links

• oxyhemoglobin - Medical Dictionary - The Free Dictionary

oxyhemoglobin. Also found in: Dictionary/thesaurus, Acronyms, Encyclopedia, Wikipedia, 0.01 sec. oxyhemoglobin /oxy·he·mo·glo·bin/ (-he″mo-glo´bin) hemoglobin that contains bound O2, a compound formed from hemoglobin on exposure ...

• Hemoglobin - Wikipedia, the free encyclopedia

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 ...

Related Pictures

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★リンクテーブル★

リンク元	「MRI」「コンピュータ断層撮影」「酸素化ヘモグロビン」「oxyhaemoglobin」「酸化ヘモグロビン」
拡張検索	「carboxyhemoglobinemia」「carboxyhemoglobin」

「MRI」

　　[★]

同

magnetic resonance imaging、核磁気共鳴画像、磁気共鳴撮像、磁気共鳴断層撮影 magnetic resonance computed tomography MR-CT、磁気共鳴映像法、磁気共鳴画像法、核磁気共鳴画像診断法

頭部MRIにて使用するシークエンス

• T1強調画像
• T2強調画像
• MR angiography

• 造影剤を使わない方法

• TOF法(time-of-flight法)

• 流入してくるプロトンの量を強調→流入する血流のみを高信号に描出

• PC法(phase contrast法)

• 流速に応じた位相の変化を利用

• 造影剤を使用する方法

• MRDSA(MR digital subtraction angiography)

• 造影剤の急速注入→適応：動静脈病変、血行動態、例えば脳動静脈奇形

• T2*強調画像：出血性病変
• ダイナミックMRI：下垂体、vascularity

Perfusion imaging：vascularity

• 3D-MRI
• FLAIR法(fluid attenuated inversion recovery)

• 頭蓋内スクリーニング(T2より病変がわかりやすい)

• 拡散強調画像 diffusion imaging

• 適応：急性期脳梗塞

• functional MRI(fMRI)：術前マッピング
• MR spectroscopy（MRS）：代謝物質

MRIの撮像条件と信号強度

		水	脂肪	骨
T1強調画像	T1WI	黒	白	黒
T2強調画像	T2WI	白	白	黒
FLAIR		黒	白	黒
拡散強調画像	DWI	黒	黒	黒

基本的な物質のMRI画像

参考2 SOR.122

T2 強 調 画 像	高信号		水					出 血 「 メ ト ヘ モ グ ロ ビ ン 」
									脂肪
					線維組織
			皮質骨 空気 血流
	低信号
		低 信 号	.	.	.	.	.	.	高 信 号
		T1強調画像

YN.J-60

• MRIの組織間信号強度
• MRIの血液信号の強度 経時的変化(脳出血)

脳のCT, MRIの比較

	CT	MRI
		T1	T2
灰白質	high	low	high
白質	low	high	low
CSF	low	low	high
血液	high	void	void

疾患とMRI

脳出血

• 超急性期：oxyhemoglobin
• 急性期：deoxyhemoglobin
• 亜急性期：methemoglobin
• 慢性期：hemosiderin

wiki_jaを引用改変

病期	ヘム鉄の性状		磁性	局在	T2WI	T1WI	CT
超急性期（24時間以内）	オキシヘモグロビン	oxyhemoglobin	Fe2+/反磁性	赤血球内	軽度高信号	軽度低信号	高吸収域
急性期（3日以内）	デオキシヘモグロビン	deoxyhemoglobin	Fe2+/常磁性	赤血球内	低信号	軽度低信号	高吸収域
急性期（7日以内）	メトヘモグロビン	methemoglobin	Fe3+/常磁性	赤血球内	低信号	高信号	高吸収域
亜急性期（2週間以内）	フリーメトヘモグロビン		Fe3+/常磁性	赤血球外	高信号	高信号	辺縁部から低下
慢性期（1か月以後）	ヘモジデリン	hemosiderin	Fe3+/常磁性	赤血球外	低信号	低信号	低吸収域

脳梗塞

• CTでは発症早期の所見は取りづらく(early CT signは除く)、12-24時間後に低吸収が出現するため、拡散強調画像(DWI)による発症1-3時間後の高信号をとらえるのが早期診断に有用である。

肝臓

SRA.482

• 正常：T1　＞筋肉、脾臓、T2　脾臓、腎臓＞　＞筋肉。
• 病変：T1　軽度低信号、T2　軽度高信号
• T1強調画像で高信号：脂肪沈着を伴う病変(脂肪肝、肝細胞癌、線種様過形成)、高蛋白貯留液を含む嚢胞性病変(粘液性嚢胞、感染後の嚢胞)、線種様過形成、常磁体物の沈着(亜急性期メトヘモグロビン)、メラニン、ガドリニウム
• T2強調画像で著明な高信号：液体の貯留　→　肝嚢胞、海綿状血管腫
• T2強調画像で低信号：水分減少を伴う病変(凝固壊死、線種様過形成)、メラニン、デオキシヘモグロビン、ヘモジデリン

DWI

• 肝臓では占拠性病変が高信号として描出される。悪性腫瘍では細胞密度が増加し水分子の拡散が制限された結果、高信号を示すと考えられている。

ADC

• 各肝腫瘍における見かけの拡散係数（ADC：apparent diffusion coefficient）を比較し、血管腫では高ADC、悪性腫瘍では低ADCであった。

血腫

参考5改変

血腫におけるヘモグロビンの変性とMRI所見
出血	血液成分	T1強調画像	T2強調画像
直後(～24時間)	オキシヘモグロビン	軽度低信号	軽度高信号
1～3日(急性期)	デオキシヘモグロビン	軽度低信号	低信号
3日～1カ月(亜急性期)	血球外メトヘモグロビン	高信号	高信号
1カ月以上(慢性期)	ヘモジデリン	軽度低信号	低信号

T1とT2

• T1が場所、T2が性質を知るために行う？

造影

• ガドリニウム：MRIで造影といえばこれ。
• 超磁性体酸化鉄粒子 SPIO：肝網内系をターゲットとした造影剤である。SPIOはKupffer細胞に貪食されリソソームにクラスター化される家庭でT2*緩和時間およびT2緩和時間を短縮させる。ゆえにKupffer細胞を含む正常肝組織の信号が低下し、含まない腫瘍とのコントラストを強調することができる。(参考1)

磁場

参考3 参考4

• 2010年現在、臨床で主流となっているMRIは1.5Tが主流。3Tも入り始めている、らしい。
• 臨床で使用可能な磁場強度の上限は厚労省が決めているらしい。

参考

• 1. 多様化する肝転移治療の選択｜肝転移の画像診断：Cancer Therapy.jp：コンセンサス癌治療

http://www.cancertherapy.jp/liver_metastasis/2007_autumn/02.html

• 2. C．産婦人科検査法 9．婦人科疾患のMRI 診断 - 日産婦誌59巻5号

http://www.jsog.or.jp/PDF/59/5905-113.pdf

• 3. MR検査室 - 慶応大学病院

http://www.hosp.keio.ac.jp/kensa/hoshasen/m0.htm

• 4. MRI開発史と科学者たち 物理学専攻 M1 24B07054 森尾豊

http://www-het.phys.sci.osaka-u.ac.jp/~higashij/lecture/coe07/4hanmorio.pdf

• 5. B．産婦人科検査法 9．婦人科疾患のMRI 診断 - 日産婦誌53巻6号

http://www.jsog.or.jp/PDF/53/5306-099.pdf

「コンピュータ断層撮影」

　　[★]

英

computed tomography CT, computerized tomography

同

CTスキャン CT scan、コンピューター断層撮影、コンピュータ断層撮影法

コンピュータ体軸断層撮影 computed axillar tomography computerized axial tomography CAT、axial computed tomography、computerized trans axial tomography、

X線CT X-ray computed tomography X-CT、CT-scanner

関

CT値

• 水：0、空気：-1000とした。脂肪は-100程度。
• 血腫：40-95　＞　灰白質：36-46　＞　白質(脂質richだから？)：2-32

脳のCT, MRIの比較

	CT	MRI
		T1	T2
灰白質	high	low	high
白質	low	high	low
CSF	low	low	high
血液	high	void	void

脳出血とCT/MRI

• 超急性期：oxyhemoglobin
• 急性期：deoxyhemoglobin
• 亜急性期：methemoglobin
• 慢性期：hemosiderin

「酸素化ヘモグロビン」

　　[★]

英

oxyhemoglobin (SP), oxygenated hemoglobin, O2Hb

同

オキシヘモグロビン、酸化ヘモグロビン

関

ヘモグロビン、メトヘモグロビン、酸素容量

[show details]

酸素化ヘモグロビン : 約 84,000 件
オキシヘモグロビン : 約 11,700 件
酸化ヘモグロビン : 約 12,900 件

「oxyhaemoglobin」

　　[★] 酸素化ヘモグロビン、オキシヘモグロビン、酸化ヘモグロビン、oxyhemoglobin

「酸化ヘモグロビン」

　　[★] オキシヘモグロビン、oxyhemoglobin

「carboxyhemoglobinemia」

　　[★]

関

カルボキシヘモグロビン

「carboxyhemoglobin」

　　[★] カルボキシヘモグロビン