Function and Structure of Hemoglobin and Myoglobin Essay

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†¦show more content†¦One of these is to a histidine residue which lies eight residues along helix F of hemoglobin, the proximal hitidine (His F8). The sixth bond is to one of the oxygen atoms in a molecule of oxygen. Near to where the oxygen binds to the heme group is another histidine residue, the distal histidine (His E7). This serves two very important functions. First, preventing neightboring hemoglobin molecules coming into contact with one another and oxidizing to the Fe3+ state, cause no longer bind to oxygen. Sencond, lowering the affinity of the heme for CO by preventing carbon monoxide binding with the most favourable configuration to the Fe2+. This is important because the protein can no longer bind oxygen once CO has bound irreversibly to the heme,. Thus, although the oxygen binding site in hemoglobin and myglobin is only a small part of the whole protein, the polypeptide chain modulates the function of the heme prosthetic group. Hemoglobin can bind four molecules of oxygen due to its four-heme groups, whereas myoglobin can only bind to one oxygen. The kinetics of oxygen binding of hemoglobin and myoglobin are quite different. Myoglogin exhibit a hyperbolic oxygen binding curve and hemoglobin exhibit a sigmoidial oxygen binding curve. The sigmodial curve suggest the the cooperative exist in the hemolglobing oxygen bind mechanism. 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