Hemoglobin - Wikipedia
The red blood cells in your blood use hemoglobin to carry oxygen from your lungs to every cell in your body. So when a person .. Whats the difference between low feritan and anemia? I am permanently Thank you and God bless. Reply. Wiad Lek. Jul 1;22(13) [Relationship between the concentration of erythrocytes or hemoglobin and the hematocrit value as determined in the. Hemoglobin has been used to determine evolutionary relationships. In vertebrates, hemoglobin is found the erythrocytes or red blood cells.
Deoxygenated hemoglobin[ edit ] Deoxygenated hemoglobin is the form of hemoglobin without the bound oxygen. The absorption spectra of oxyhemoglobin and deoxyhemoglobin differ. This difference is used for the measurement of the amount of oxygen in a patient's blood by an instrument called a pulse oximeter. This difference also accounts for the presentation of cyanosisthe blue to purplish color that tissues develop during hypoxia.
Having multiple subunits contributes to hemoglobin's ability to bind oxygen cooperatively as well as be regulated allosterically. The lowest-energy form of oxygen, and the lowest energy forms of the relevant oxidation states of iron, are these: Iron II tends to exist in a high-spin 3d6 configuration with four unpaired electrons. Iron III 3d5 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 electronsnot diamagnetic.
Thus, a non-intuitive e. The two logical possibilities to produce diamagnetic no net spin Hb-O2 are: Both low-spin iron and singlet oxygen are diamagnetic.
However, the singlet form of oxygen is the higher-energy form of the molecule. Here, the iron has been oxidized has lost one electronand the oxygen has been reduced has gained one electron. Here, the iron has been oxidized by two electrons, and the oxygen reduced by two electrons.
X-ray photoelectron spectroscopy suggests iron has an oxidation state of approximately 3.
The Role Of Iron In The Body
Infrared vibrational frequencies of the O-O bond suggests a bond length fitting with superoxide a bond order of about 1. The diamagnetism in this configuration arises from the single unpaired electron on superoxide aligning antiferromagnetically with the single unpaired electron on iron in a low-spin d5 stateto give no net spin to the entire configuration, in accordance with diamagnetic oxyhemoglobin from experiment.Erythrocytes, Hemoglobin & the Iron Cycle
Model 3 leads to unfavorable separation of charge and does not agree with the magnetic dataalthough it could make a minor contribution as a resonance form.
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 methemoglobinwhen not accompanied by superoxide.
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 diamagnetic, high-energy, singlet oxygen molecule 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 energycausing 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. Cooperativity[ edit ] A schematic visual model of oxygen-binding process, showing all four monomers and hemesand protein chains only as diagrammatic 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 illustrationtugging 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.
Hemoglobin - New World Encyclopedia
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. As oxygen binds to one monomer of hemoglobin, the tetramer's conformation shifts from the T tense state to the R relaxed state.
This shift promotes the binding of oxygen to the remaining three monomer's heme groups, thus saturating the hemoglobin molecule with oxygen. The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule, with the first molecules of oxygen bound influencing the shape of the binding sites for the next ones, 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. As a consequence, the oxygen binding curve of hemoglobin is sigmoidalor 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.
Nitric oxide can also be transported by hemoglobin; it 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.
CO competes with oxygen at the heme binding site. Hemoglobin's binding affinity for CO is 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, carbon monoxide 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 carboxyhemoglobinwhich 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. All of these bind to iron in heme without changing its oxidation state, but they nevertheless inhibit oxygen-binding, causing grave toxicity.
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. 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 anhydrasecarbon dioxide reacts with water to give carbonic acidwhich decomposes into bicarbonate and protons: 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. The Bohr effect favors the T state rather than the R state.
Conversely, when the carbon dioxide levels in the blood decrease i. A reduction in the total binding capacity of hemoglobin to oxygen i. 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 lungsand efficient in unloading unloading O2 in tissues.
This phenomenon, where molecule Y affects the binding of molecule X to a transport molecule Z, is called a heterotropic allosteric effect. Hemoglobin in organisms at high altitudes has also adapted such that it has less of an affinity for 2,3-BPG and so the protein will be shifted more towards its R state.
In its R state, hemoglobin will bind oxygen more readily, thus allowing organisms to perform the necessary metabolic processes when oxygen is present at low partial pressures. The major final product of heme degradation is bilirubin, a yellow waste product. Increased levels of this chemical are detected in the blood if red cells are being destroyed more rapidly than usual.
- Interactive Tools
Improperly degraded hemoglobin protein or hemoglobin that has been released from the blood cells can clog small blood vessels, especially the delicate blood filtering vessels of the kidneys, causing kidney damage. Iron is stored in the liver or recycled into new hemoglobin. Hemoglobin and nitrogen-fixing plants Many species of leguminous plants, and some nonleguminous plants, are capable of taking atmospheric nitrogen from the air and converting it to nitrate for food for the plant.
This process, called nitrogen fixationoccurs when special kinds of bacteriaoften species of the genus Rhizobium, infect the roots of the plant and produce nodules there. Remarkably, these nitrogen-fixing nodules contain quantities of hemoglobin. Hemoglobin is otherwise unknown in the plant kingdom. The hemoglobin appears to enhance nitrogen fixation indirectly, by controlling the partial pressure of oxygen in the nodule.
Role in disease and diagnosis Decreased levels of hemoglobin, with or without an absolute decrease of red blood cellsleads 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, and 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 cellsassociated jaundice is caused by the hemoglobin metabolite bilirubin, and the circulating hemoglobin can cause renal failure. Mutations in the globin chain are associated with haemoglobinopathies, such as sickle-cell anemia and thalassemia. Sickle-cell anemia is a recessive genetic disease which causes a single amino-acid defect a valine molecule replaces a molecule of glutamic acid in one of the the protein chains of hemoglobin.
This defect causes the red blood cells to become deformed when oxygen is scarce as when the individual is exercising strenuously and they combine with each other, forming blockages to blood flow at just the time when the body needs oxygen the most. As a result, people with sickle-cell anemia tend to have intermittent illness and have shorter than normal life spans. There is a group of genetic disorders, known as the porphyrias, that are characterized by errors in metabolic pathways of heme synthesis.
To a small extent, hemoglobin A slowly combines with glucose at a certain location in the molecule. The resulting molecule is often referred to as Hb A1c. As the concentration of glucose in the blood increases, the percentage of Hb A that turns into Hb A1c increases. In diabetics whose glucose usually runs high, the percent Hb A1c also runs high. Because of the slow rate of Hb A combination with glucose, the Hb A1c percentage is representative of glucose level in the blood averaged over a longer time typically 3 months.
Hemoglobin levels are among the most commonly performed blood tests, usually as part of a full blood count. For example, hemoglobin levels are used in testing for glucose levels. Glucose levels in blood can vary widely each hour, so one or only a few samples from a patient analyzed for glucose may not be representative of glucose control in the long run. For this reason, a blood sample may be analyzed for Hb A1c, which is more representative of glucose control averaged over a longer time period.
People whose Hb A1c runs 6. Hb A1c values which are more than 7. This test is especially useful for diabetics. Other biological oxygen-binding proteins Hemoglobin is by no means unique; there are a variety of oxygen transport and binding proteins throughout the animal and plant kingdom.
Other organisms, including bacteriaprotozoans and fungiall have hemoglobin-like proteins whose known and predicted roles include the reversible binding of gaseous ligands. It is found in the muscle tissue of many vertebrates including humans, and especially common in diving mammals such as whales and seals gives muscle tissue a distinct red or dark gray color.
What Are Red Blood Cells? - Health Encyclopedia - University of Rochester Medical Center
Myoglobin is very similar to hemoglobin in structure and sequence, but it is not arranged in tetramers, it is a monomer and lacks cooperative binding, and is used to store oxygen rather than transport it. It is the second most common oxygen transporting protein found in nature. Hemocyanin is found in the blood of many arthropods and molluscs.
Hemocyanis uses copper prosthetic groups instead of iron heme groups, and it is blue in color when oxygenated. Some marine invertebrates and a few species of annelid use this iron containing non-heme protein to carry oxygen in their blood. Also known as Vanadium Chromagen, it is found in the blood of Sea squirts and are hypothesized to use the rare metal Vanadium as its oxygen binding prosthetic group; however, this hypothesis is unconfirmed.
It is found in many annelidsincluding earthworms. A giant free-floating blood protein, it contains many dozens, even hundreds, of iron heme containing protein subunits bound together into a single protein complex, with a molecular masses greater than 3. It is only seen in the mollusk Pinna squamosa.
It is a brown manganese-based porphyrin protein. This is found 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.