Structural Biochemistry/Protein function/Hemoglobin - Wikibooks, open books for an open world
The Structure−Function Relationship of Hemoglobin in Solution at Atomic Interactions of Hemoglobin and Myoglobin with Their Ligands CN, CO, and O2. Because myoglobin and hemoglobin each bind oxygen, we can assume that there Myoglobin has a highly folded and compact structure that has 8 separate and to explain the different biological functions of hemoglobin and myoglobin. Free Essay: Myoglobin consist of single polypeptide chain that made up of amino acid and ahs a size of 18 kDa. Its three-dimensional structure was first.
The distal histidine amino acid from the hemoglobin protein molecule further stabilizes the O2 molecule by hydrogen-bonding interactions. Myoglobin is a protein molecule that has a similar structure and function to hemoglobin.
It is a smaller monomer of polypeptide structure, a globular protein with amino acids and prosthetic heme group binds to proximal histidine group while a distal histidine group interact on the other side of the plane.
It binds and stores oxygen without concerning cooperativity. Most importantly, it is the first protein structure to be studied. Myoglobin follows the Michaelis-Menten Kinetic graph as seen from the graph above.
Hemoglobin and Myoglobin
It follows the Michaelis-Menten kinetics because it is a simple chemical equilibrium. Function[ edit ] The binding affinities for oxygen between myoglobin and hemoglobin are important factors for their function. Both myoglobin and hemoglobin binds oxygen well when the concentration of oxygen is really high E.
Since hemoglobin binds oxygen less tightly than myoglobin in muscle tissues, it can effectively transport oxygen throughout the body and deliver it to the cells.
Myoglobin, on the other hand, would not be as efficient in transferring oxygen. It does not show the cooperative binding of oxygen because it would take up oxygen and only release in extreme conditions.
Myoglobin has a strong affinity for oxygen that allows it to store oxygen in muscle effectively. This is important when the body is starved for oxygen, such as during anaerobic exercise. During that time, carbon dioxide level in blood streams is extremely high and lactic acid concentration build up in muscles.
Both of these factors cause myoglobin and hemoglobins to release oxygen, for protecting the body tissues from getting damaged under harsh conditions. If the concentration of myoglobin is high within the muscle cells, the organism is able to utilize the oxygen in its lungs for a much longer period of time. The heme resides in a small hydrophobic cleft within each polypeptide. The hydrophobic residues will be shown in green, while hydrophilic are colored red. There is one heme associated with myoglobin.
There are four hemes found in hemoglobin, one in each of the subunits. Therefore, myoglobin binds reversibly to only one oxygen molecule, while and hemoglobin binds four.
These differences help to explain the different biological functions of hemoglobin and myoglobin. Hemoglobin is used to transport oxygen over large distances from the lungs to all tissueswhereas myoglobin is present in muscle and behaves as a local "storage" reservoir of oxygen.
Also, due to the intrinsic nature of hemoglobin, it can more precisely control the binding and release of oxygen in the appropriate areas of the body. The internal arrangement of heme in this cleft is very similar in myoglobin and hemoglobin.
Incidentally, when a metal ion binds to a porphyrin, which has a great number of conjugated double bonds, it will lead to a compound that is highly colored. This is why blood is red.
In plants, the porphyrin is chelated with a magnesium ion, giving chlorophyll a greenish-blue color. This prosthetic group is physically held in the cleft by hydrophobic interactions as well as a coordinate covalent bond between the iron atom and a nearby nitrogen atom, belonging to the side chain of a histidine residue. This histidine residue is often referred to as the proximal histidine.
On the side of the heme group opposite the proximal histidine, where oxygen reversibly binds, is another histidine residue called the distal histidine.
This residue serves two very important functions in the polypeptide. First, it prevents oxidation of the iron ion to a higher oxidation state by any number of possible nearby oxidizing agents. Secondly, this histidine residue acts to reduce carbon monoxide CO binding to the heme.
If the distal histidine was absent, even low levels of CO would greatly interfere with oxygen binding. The heme group alone in the absence of the surrounding protein of myoglobin or hemoglobin has a much greater bonding affinity for carbon monoxide than for oxygen.
Allostery and Hemoglobin The physical process of binding and releasing oxygen by hemoglobin has a marked effect on its three-dimensional structure.
Structural Biochemistry/Protein function/Heme group/Myoglobin
Hemoglobin in its deoxygenated state has a low affinity for oxygen compared to myoglobin. When oxygen is bound to the first subunit of hemoglobin it leads to subtle changes to the quaternary structure of the protein. Hemoglobin also helps in the transportation of carbon dioxide and hydrogen ions back to the lungs. Hemoglobin or Haemoglobin is able to bind to gaseous nitric oxide NO as well as O2. As red blood cells passes through the capillary beds of the lungs, gills in fishor other respiratory organs, oxygen is diffused into the erythrocytes and hemoglobin binds O2 and NO.
Myoglobin & Hemoglobin
Hemoglobin then unloads its cargo in the capillaries. There O2 is able to diffuse into the body cells. The NO relaxes the walls of the capillaries, allowing them to expand which in effects helps the delivery of O2 to the cells.
JPG px Hemoglobin consists of four subunits, each with a cofactor called a heme group that has an iron atom center. The iron is the main component that actually binds to oxygen, thus each hemoglobin molecule is able to carry four molecules of O2. Cooperation among the four subunits of the hemoglobin molecule is necessary for the efficient transportation of O2. The four subunits of hemoglobin actually bind to oxygen cooperatively, the binding of oxygen to one site of the four subunits will increase the likelihood of the remaining sites to bind with oxygen as well.
Hemoglobin is a protein that is used to carry oxygen through the blood stream from the lungs to the tissues. This is important for survival. Hemoglobin has a lower affinity for oxygen the lower the concentration of oxygen gets. This has great implications for the human body and has helped us adapt very effectively. The lower affinity and lower concentrations means that when we are working out, our bodies are low on oxygen which means hemoglobin has less affinity for oxygen and can more easily drop the oxygen off at human tissues.
This gives us greater oxygen in our oxygen dependent state. On the other hand, when oxygen concentration is high, the hemoglobin has a higher affinity for oxygen and therefore does not drop the oxygen where it is not needed.
This is a very complex and smart system that has evolved to keep hemoglobin as an important biological molecule for a very long time. On the otherhand, the cousin of hemoglobin, myoglobin is used to store oxygen in muscles.
- Structural Biochemistry/Protein function/Hemoglobin
- Structure-function relationships in unusual nonvertebrate globins.
This myoglobin has a slighty higher affinity for oxygen than hemoglobin especially at lower levels. This is because myoglobin has an easier job in that it only needs to store oxygen and release it for the muscles, while hemoglobin also has to transport the oxygen and release it in the correct areas. Hemoglobin is coded for by DNA just like all the other proteins.
Alterations or mutations to hemoglobin causes many blood related diseases such as sickle-cell anemia, where the cell structure is distorted and can no longer carry as much oxygen in the correct way as a normal blood cell. This highlights the underlying ideal in structural biochemistry in that structure determines function.
Myoglobin & Hemoglobin
The sickle cell anemia case is extremely interesting because it shows us how and why diseases develop. The gene for sickle cell anemia also provides protection against malaria. Therefore, in countries where malaria presented problems, there was an higher than average amount of individuals carrying the sickle cell anemia gene. The heterozygous state is best because it does not allow sickle cell anemia to develop while still preventing malaria.
Whereas, the homozygous states would produce individuals either struck with sickle cell anemia or malaria.
This is why in malaria ridden areas, there is a higher than average number of people who are heterozygous for sickle cell anemia which is also why this disease does not die out! The carrier state is actually selected by nature. Cooperation refers to the interactions among active sites, in the case of hemoglobin, cooperation allows the binding of oxygen to be increased as one site is filled, the remaining active sites will be more likely to bind to O2 as well.
The associated movement of the histdine-containing group will result in a conformational change to the rest of the hemoglobin structure. The COO- group is now interacting with the alpha-beta interface which causes conformational changes of neighboring active sites.
These conformational changes will result in an increase of O2 affinity to hemoglobin. Allostery[ edit ] Hemoglobin is an allosteric protein.