why does hydrophilic residues of myoglobin replaced by hydrophobic residues of hemoglobin?
Doesn't make sense..
The substitution of hydrophilic residues in myoglobin with hydrophobic residues in hemoglobin is an evolutionary adaptation that influences the function and properties of these proteins.
To understand why this substitution occurred, it's important to first look at the roles and environments in which myoglobin and hemoglobin operate.
Myoglobin is a single-chain protein primarily responsible for oxygen storage in muscle tissues. It needs to have a strong affinity for oxygen to effectively capture and retain it until needed. Myoglobin functions in an intracellular environment, where polar (hydrophilic) residues can interact with water molecules readily.
On the other hand, hemoglobin is a complex protein composed of four subunits. It acts as an oxygen transporter, picking up oxygen from the lungs and delivering it to various tissues throughout the body. Hemoglobin operates in the bloodstream and needs to be able to release oxygen efficiently in tissues with low oxygen levels. In this extracellular environment, interacting with water is less important, but interacting with hydrophobic regions becomes advantageous.
The substitution of hydrophilic residues in myoglobin with hydrophobic residues in hemoglobin promotes the ability of hemoglobin to undergo conformational changes when binding to or releasing oxygen. The hydrophobic interactions between these residues allow for more efficient oxygen delivery and release in the extracellular environment of the bloodstream.
This substitution likely occurred through evolutionary processes, driven by natural selection. Over time, organisms with hemoglobin variants that possessed hydrophobic residues may have had a selective advantage in terms of enhanced oxygen delivery capabilities, leading to their survival and reproduction.
In summary, the replacement of hydrophilic residues in myoglobin with hydrophobic residues in hemoglobin is an adaptation that enhances the ability of hemoglobin to function as an efficient oxygen transporter in the extracellular environment of the bloodstream.