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The key difference between haemoglobin and myoglobin is that haemoglobin is a globin protein that transfers oxygen to all parts of the organism’s body while myoglobin is a globin protein that transfers oxygen to muscle cells only.
Haemoglobin vs. Myoglobin
Respiration is a fundamental process of life. Almost every organism requires the transportation of oxygen to all the cells of its body for its survival. Haemoglobin and myoglobin are two basic globin proteins in living organisms that binds oxygen and transfer them to the cells. But, there exist a number of differences between them. Haemoglobin transfers oxygen from lungs to all parts or cells of the body in vertebrates as well as some invertebrates while myoglobin transfers oxygen to muscle cell only. Haemoglobin is composed of 4 polypeptide chains while myoglobin is composed of the single polypeptide chain. Haemoglobin is found in the blood stream while myoglobin is found in muscle cells.
What is Haemoglobin?
Haemoglobin is a multi-subunit globin protein with a quaternary structure and is made up of four polypeptide chains, two α and two β subunits. Each alpha chain is made up of 144 residues and each beta chain is made up of 146 residues. The opposites subunits like alpha and beta associate more strongly than similar subunits alpha-alpha or beta-beta. It is an iron-containing metalloprotein. In haemoglobin each of the four subunits is attached to a non-protein, prosthetic haem group, where oxygen molecule binds. So, its mean that haemoglobin can bind four oxygen molecules with four haem groups of each chain. It has low oxygen affinity in its deoxygenated state, but when first oxygen molecule binds to haemoglobin it leads to the change in its structure that makes the binding of other oxygen molecules easier. This process is called an allosteric (through space) interaction/ cooperativity. Haemoglobin is found in excess in red blood cells and give them a red colour. It involves in the transportation of oxygen and carbon dioxide to or from all parts of the body. It also involves in the metabolism of erythrocytes and also maintains the pH of blood.
Haemoglobin is divided into the following six types.
- Haemoglobin A1 (Hb-A1).
- Haemoglobin A2 (Hb-A2).
- Haemoglobin A3 (Hb-A3).
- Embryonic haemoglobin.
- Glycosylated haemoglobin.
- Foetal Haemoglobin (Hb-A1).
What is Myoglobin?
Myoglobin is a monomer globin protein which exhibits secondary structure. It is composed of a single polynucleotide chain which is composed of 153 residues. It has a single heam group attached to its single polypeptide chain. So, a single oxygen molecule may bind to it. But, its binding capacity is higher than that of haemoglobin, so it serves as an oxygen-storing protein which releases during muscle functioning. It is found in muscle cells and provides oxygen to them on the requirement. It helps the body at the starving conditions of oxygen, especially in the anaerobic conditions. It also regulates the body temperature. Myoglobin does not have any type.
- Haemoglobin is a globin protein that transfers oxygen from the lungs to all parts of the body while myoglobin is a globin protein that transfers oxygen to the muscle cells only.
- Haemoglobin has tetramer structure while myoglobin is a monomer in structure.
- Haemoglobin is composed of 4 polypeptide chains whereas myoglobin is composed of the single polypeptide chain.
- Haemoglobin is present in red blood cells while myoglobin is found in muscle
- Haemoglobin has four haem groups so it can bind four oxygen molecules, but myoglobin has a single haem group so it can bind a single oxygen molecule because haem group is the place of binding of the oxygen
- Haemoglobinmay bind with O2, CO2, CO, NO, BPH and H+ while myoglobin may bind with O2 only.
- Haemoglobin has 64 kDa molecular weight whereas myoglobin has a molecular weight of 16.7 kDa.
- Haemoglobin has a low affinity to bind with oxygen while myoglobin has a high affinity to bind with oxygen.
- Haemoglobin involves in the transportation of oxygen and carbon dioxide to or from all parts of the body, in the metabolism of erythrocytes and also maintains the pH of blood while myoglobin is found in muscle cells and provide oxygen to them on the requirement and also regulates the body temperature.
From the above discussion, it is concluded that haemoglobin is a tetramer composed of four polynucleotide chains and transport oxygen and carbon dioxide to all parts of the body while myoglobin is a monomer composed of single nucleotide chain and transport oxygen to muscle cells only on the requirement.