The Bohr effect is a physiological phenomenon first described in 1904 by the Danish physiologist Christian Bohr: the affinity of binding oxygen hemoglobin (see the oxygen-hemoglobin dissociation curve) is inversely proportional to the acidity and concentration of carbon dioxide. Because carbon dioxide reacts with water to form carbonic acid, an increase in CO 2 results in a decrease in blood pH, so that the hemoglobin protein releases its oxygen charge. In contrast, a decrease in carbon dioxide provokes an increase in pH, which results in hemoglobin taking up more oxygen.
Video Bohr effect
Experimental findings
In the early 1900s, Christian Bohr was a professor at the University of Copenhagen in Denmark, well known for his work in the field of respiratory physiology. He has spent the last two decades studying the solubility of oxygen, carbon dioxide, and other gases in various liquids, and has done extensive research on hemoglobin and its affinity for oxygen. In 1903, he began working with Karl Hasselbalch and August Krogh, two colleagues at the university, in an experimental attempt to replicate the work of Gustav von HÃÆ'¼fner, using whole blood as a substitute for hemoglobin solution. HÃÆ'¼fner suggested that the oxygen-hemoglobin-binding curve was hyperbolic, but after extensive experiments, the Copenhagen group decided that the curve was actually sigmoidal. Furthermore, in the process of plotting many dissociation curves, it soon became clear that high partial pressures of carbon dioxide caused the curve to shift to the right. Further experimentation while varying the concentration of CO 2 quickly provides conclusive evidence, confirming the existence of what will soon be known as the Bohr effect.
Controversy
There is some debate as to whether Bohr was the first to discover the relationship between CO 2 and oxygen affinity, or whether Russian physiologist Bronislav Verigo beat him, allegedly discovered the effect in 1898, six years before Bohr. Although this was never proven, Verigo did publish a paper on the hemoglobin-CO 2 relationship in 1892. His proposed model was flawed, and Bohr harshly criticized it in his own publications.
Another challenge for Bohr's invention comes from within his lab. Although Bohr quickly took full credit, his colleague Krogh, who invented the tool used to measure gas concentration in his experiments, maintained throughout his life that he himself was in fact the first to demonstrate its effect. Although there is some evidence to support this, retroactively changing the name of the famous phenomenon would be very impractical, so it remains known as the Bohr effect.
Maps Bohr effect
Physiological role
Although this reaction is usually very slow, the carbonic anhydrase enzyme (present in red blood cells) drastically accelerates conversion to bicarbonate and proton. This causes a decreased blood pH, which drives the dissociation of oxygen from hemoglobin, and allows the surrounding tissue to get enough oxygen to meet their demands. In areas where high oxygen concentrations, such as the lungs, oxygen binding cause hemoglobin to release protons, which recombine with bicarbonate to remove carbon dioxide during respiration. This opposite protonation and deprotonation reaction occurs at the same rate, resulting in a slight change in overall blood pH.
The Bohr effect allows the body to adapt to changing conditions and allows it to supply extra oxygen to the tissues that need it most. For example, when the muscles are undergoing heavy activity, they need large amounts of oxygen to do cell respiration, which results in CO 2 (and therefore HCO 3 - and H ) as a by-product. These waste products lower blood pH, which increases oxygen delivery to the active muscles. Carbon dioxide is not the only molecule that can trigger the Bohr effect. If muscle cells do not receive enough oxygen for cell respiration, they use lactic acid fermentation, which releases lactic acid as a by-product. This increases blood acidity far more than CO 2 alone, reflecting the need for larger cells for oxygen. In fact, under anaerobic conditions, the muscle produces lactic acid very quickly so that the blood pH passing through the muscle will drop to about 7.2, causing hemoglobin to begin releasing about 10% more oxygen.
Relationship to body size
The Bohr effect depends on the allosteric interaction between hemes of hemoglobin tetramer, the mechanism first proposed by Max Perutz in 1970. Hemoglobin exists in two conformations: high affinity R state and low affinity T status. When high levels of oxygen concentration, such as in the lungs, state R is preferred, allowing the maximum amount of oxygen to be bound to hemes. In capillaries, where the oxygen concentration level is lower, the T state is preferred, to facilitate the delivery of oxygen to the tissues. The Bohr effect depends on this allostery, as increased CO 2 and H help stabilize the T state and ensure greater oxygen delivery to the muscles during periods of high cellular respiration. This is evidenced by the fact that myoglobin, a monomer without alosophes, does not show Bohr effect. Mutant hemoglobin with weaker allostery may show less Bohr effect. For example, in the Hiroshima variant haemoglobinopathy, allostery in hemoglobin is reduced, and the Bohr effect is reduced. Consequently, during the exercise period, mutant hemoglobin has a higher affinity for oxygen and tissues may experience mild oxygen deprivation.
Stabilization t-state
When the hemoglobin is in its T-state, the N-terminal amino group of the -subunite and histidine C-terminals of the protonated particles, gives them a positive charge and allows these residues to participate in ionic interactions with carboxyl groups. on the nearest residue. This interaction helps withstand hemoglobin in T state. The decrease in pH (increase in acidity) stabilizes this state even more, because the decrease in pH makes this residue even more likely to be protonated, amplifying ionic interactions. In the R state, ionic pairs are absent, which means that the state stability of R increases when the pH increases, since this residue tends to be undiprotonated in a more basic environment. The Bohr effect works simultaneously to destabilize the high affinity R state and stabilize the low affinity T state, leading to an overall decrease in oxygen affinity. This can be visualized on the oxygen-hemoglobin dissociation curve by shifting the entire curve to the right.
Karbon dioksida juga dapat bereaksi secara langsung dengan gugus amino N-terminal untuk membentuk karbamat, sesuai dengan reaksi berikut:
CO 2 forms carbamates more often with a T state, which helps stabilize this conformation. This process also creates protons, which means that the formation of carbamates also contributes to the strengthening of ionic interactions, further stabilizing the T state.
Custom case
Marine mammals
Exceptions to the well-supported relationship between animal body size and hemoglobin sensitivity to pH changes were found in 1961. Based on their size and weight, many marine mammals are hypothesized to have very low and almost negligible Bohr effects.. However, when their blood is examined, this is not the case. Humpback whales weighing 41,000 kilograms have observations value of 0.82, which is roughly equivalent to the magnitude of Bohr's influence in 0.57 kg of guinea pigs. This powerful Bohr effect is hypothesized to be one of many marine mammal adaptations for deep dives, long, because it allows almost all of the oxygen bound to hemoglobin to dissociate and supply the whale body while underwater. Examination of other marine mammal species supports this. In pilot and dolphin whales, which are primarily surface feeders and seldom dive for more than a few minutes, is 0.52, proportional to the cow, which is much closer to the amount of Bohr effect expected for animals of their size.
Carbon monoxide
Another special case of the Bohr effect occurs when carbon monoxide is present. This molecule serves as a competitive inhibitor for oxygen, and binds hemoglobin to form carboxyhaemoglobin. The haemoglobin affinity for CO is about 250 times stronger than its affinity for O 2 , which means that it is highly unlikely to dissociate, and once bound, it blocks the binding of O 2 to the subunit that. At the same time, the CO is structurally quite similar to O 2 to cause carboxyhaemoglobin to support the R state, increasing the oxygen affinity of the remaining empty subunits. This combination significantly reduces oxygen delivery to body tissues, which makes carbon monoxide highly toxic. This toxicity is reduced slightly by increasing the strength of the Bohr effect in the presence of carboxyhaemoglobin. This increase is ultimately due to differences in the interaction between the heme groups in the carboxyhemoglobin relative to the oxygenated hemoglobin. This is most evident when oxygen concentrations are very low, as a last resort when the need for oxygen delivery is important. However, the physiological implications of this phenomenon remain unclear.
See also
- Allosteric rules
- Haldane effect
- The root effect
References
External links
- Impact of training
Source of the article : Wikipedia
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