Function and Structure of Hemoglobin and Myoglobin

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Myoglobin consist of single polypeptide chain that made up of 153 amino acid and ahs a size of 18 kDa. Its three-dimensional structure was first determined by X-ray crystallography by John Kendrew in 1957. Myoglobin is a typical globular protein in that it is a highly folded compact structure with most of the hydrophobic amino acid residues buried in the interior and many of the polar residues on the surface. X-ray crystallography revealed that the single polypeptide chain of myoglobin consist of entirely of eight (labelled A-H) alpha-helical. Within a hydrophobic crevice formed by the folding polypeptide chain is the heme prosthetic group. This nonopolypepetide unit is noncovalently bound to myoglobin and is essential for the biological activity of the protein.

A three-dimensional structure of hemoglobin is determined by X-ray crystallography showed hemoglobin is made up of four polypeptide chains, each of those chains has a very similar three-dimensional structure to the single polypeptide chain in myoglobin. The major type of hemoglobin found in adults (HbA) is made up of two different polypeptide chains: the alpha-chain that consists of 141 amino acids residues, and the beta-chain of 146 residues. Each chain, like that in myoglobin consist of eight alpha-helices and each contains a heme prosthetic group. Therefore, hemoglobin can bind four molecules of oxygen. The four polypeptide chains, two alpha and teo beta, are packed tightly together in a tetrahedral array to form an overall spherically shaped molecule that is held together by multiple noncovalent interactions.

The heme prosthetic group, a protoporphrin IX ring structure with an iron atom ion the ferrous (Fe2+) oxidation state exist in both in myoglobin and he...

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...at high altitude, the BPG level increases, allowing Hemoglobin to release O2 more easily. However BPG is absent in most fetal hemoglobin as they lack of beta chain and instead of gamma chain to have a higher oxygen binding affinity so it optimise the transfer of oxygen from the maternal to the detal circulation.

Sickle cell anemia is the most common in hemoglobin mutation diseases due to mutation to beta-blobin gene. The substitution of valine for glutamate at position 6 of the beta chains paces a nonpolar residue on the outside of hemoglobin S. the oxygen affinity and allosteric properties of hemoglubin are virtually unaffected by this changes. However, this alternation markedly reduces the solubility of the deoxygenated but not the oxygenated form of hemoglobin. Thus, sicking occurs when there is a high concentration of the deoxygenated form of hemoglobin.

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