The key difference between hemoglobin and myoglobin is that hemoglobin is found in red blood cells, and it has a tetrameric structure while myoglobin is found in muscles and it has a monomeric structure.
Both hemoglobin and myoglobin are proteins that have the oxygen-carrying capacity. Since the basic function of both proteins is the same but they have many differences in them. Hemoglobin is present in red blood cells. Myoglobin is principally found in muscle cells.
Hemoglobin is composed of heme and globin chain. Heme is further composed of iron and protoporphyrin. The structure of hemoglobin is tetrameric. Two of its polypeptide chains are alpha chains and two beta chains. While the structure of myoglobin is monomeric. It contains a single polypeptide chain. Myoglobin is composed of heme and four pyrrole rings which are attached by methine bridges.
Hemoglobin is also written as Hb while myoglobin is written as Mb. The key role of hemoglobin is to transfer oxygen to the whole body cells when the blood circulates in the body. While myoglobin delivers oxygen to only muscles. Myoglobin carries oxygen from hemoglobin to mitochondria of the muscle cell, and this oxygen is used for energy production in the process of respiration. Hemoglobin has more affinity for carbon monoxide than oxygen while myoglobin has no affinity for CO. Haemoglobin can also bind with CO2, NO and hydrogen ions.
The functions of hemoglobin can be described as; it gives a red color to blood due to the presence of iron. It is the carrier of oxygen and CO2. It played the role of physiologically active catabolite. It maintains the pH of blood. It also plays a part in RBCs metabolism. The functions of myoglobin can be described as; it has the ability to store oxygen which makes the muscle to work more effectively. It also helps the body in anaerobic situations and in starvation. Myoglobin also plays a role in the regulation of body temperature. The central metal in both proteins is iron, and both are globular proteins. The ligand of both proteins is oxygen. The types of hemoglobin are Hb-A1, Hb-A2, Hb-A3, embryonic hemoglobin, fetal hemoglobin, and glycosylated hemoglobin. Myoglobin is not further divided into types.
Comparison chart
| Basis | Haemoglobin | Myoglobin |
| Definition | It is a protein which is found in red blood cells, and it has an oxygen carrying capacity. | It is a protein which is found in muscle cells. It has also an oxygen carrying capacity. |
| Composition | It is composed of heme and globin chains. Heme is further composed of iron and protoporphyrin. | It is composed of heme and four pyrrole rings which are attached by methine bridges. |
| Polypeptide chains | Two of its polypeptide chains are alpha, and two are beta. | It contains a single polypeptide chain. |
| Structure type | It has a tetrameric structure. | It has a monomeric structure. |
| Binding and storage ability | It has the ability to bind oxygen, but it cannot store oxygen. | It can bind and also store oxygen. |
| Subtypes | The types of hemoglobin are Hb-A1, Hb-A2, Hb-A3, embryonic hemoglobin, fetal hemoglobin, and glycosylated hemoglobin. | Myoglobin is not further divided into subtypes. |
| Central metal and ligand | Central metal is atom and ligand is oxygen. | Central metal is atom iron, and the ligand is oxygen. |
| Affinity for other gases | It has more affinity for CO than oxygen. It can also bind with CO2, NO and hydrogen ions. | It has the ability to bind with oxygen only. |
| Function | It transports oxygen in the whole body when blood circulates. | It carries oxygen from hemoglobin to mitochondria of the muscle cell. This oxygen is used in aerobic respiration. |
| Other functions | Other functions are, it gives a red color to blood due to the presence of oxygen. It also contributes to the metabolism of RBCs. They also play the role of physiological active catabolites. Haemoglobin also helps in maintaining the pH of blood. | One of its important functions is to store oxygen for muscle functions. It also helps in anaerobic conditions and in starvation. the It also contributes to temperature maintenance of the body. |
What is Haemoglobin?
Hemoglobin is a type of protein which is found in RBCs and has oxygen carrying capacity. It has a tetrameric structure and globular in shape. It is composed of heme and globin chain. Heme is further composed of iron and protoporphyrin. Each alpha unit further consists of 144 residues while each beta unit further consists of 146 residues. The key role of hemoglobin is to transport oxygen throughout the body when blood circulation takes place. It has more affinity for CO than oxygen. That is the reason for the “silent death” of the persons sleeping in rooms when the gas heaters are remained on during the night. It can also bind with CO2, NO and hydrogen ions. Hemoglobin gives a characteristic red color to blood due to the presence of oxygen. It also plays a role in red blood cells metabolism. It helps in maintaining the pH of blood. They are active catabolites. In short form, hemoglobin is also written as Hb. The normal range of hemoglobin for males is 13 to 16 mg per dl while the normal range for females is 12 to 14 mg per dl. The deficiency of hemoglobin is called anemia. Its oxygen binding curve is the sigmoid type.
What is Myoglobin?
Myoglobin is also a protein which is found in muscle cells, and it also has an oxygen carrying capacity. It also has a globular shape, but it is a monomeric protein. It contains only a polypeptide chain. It contains iron and four pyrrole rings which are attached by methine bridges. It binds with oxygen more tightly and firmly. It has not binding capability with other gases. Its oxygen binding curve is the hyperbolic type. In short form, it is also written as Mb. Its central atom is also iron just like hemoglobin and ligand is oxygen. Its extra quality is that it not only binds with oxygen but also can store it which helps the body in the conditions when oxygen supply is deficient. It picks up oxygen from hemoglobin and transfers it to mitochondria of the muscle cell where it is used in aerobic respiration. It also helps the body in temperature regulation. It also helps during the starvation condition.
Key Differences between Haemoglobin and Myoglobin
- Hemoglobin is an oxygen-binding protein which is found in RBCs while myoglobin is also a protein which has the oxygen-carrying capability, but it is found in muscles.
- Hemoglobin has a tetrameric structure while myoglobin has a monomeric structure.
- Myoglobin can store oxygen also, but hemoglobin cannot store it.
- Hemoglobin has further subtypes the important type of which are, Hb A1, Hb A2, and Hb f. Myoglobin does not have further subtypes.
- Hemoglobin has two alpha chains and two beta chains while myoglobin has a single polypeptide chain.
- Haemoglobin also has an affinity for some other gases like CO, CO2 and NO, etc. While myoglobin does not have an affinity for other gases.
Conclusion
Both hemoglobin and myoglobin are proteins which have the oxygen-carrying ability. Both have differences in their structure and functions. It is important for biology students to know these differences. In the above article, we learned thoroughly about hemoglobin and myoglobin.