Question

Describe the concept of cooperativity increase substrate binding affinity and provide an example.

Answer 1

Molecular binding between different molecules stabilises the physical association of molecules. Cooperative binding occurs between molecular species, it can affect the rate of enzyme catalysed reactions. A model that explains the cooperative binding is called cooperative binding model. In this case the enzyme has more than one subunit and active site. In cooperative binding model binding of one substrate makes easier to bind another molecule of the substrate, it means after binding of the first substrate the newly formed second subunit has an affinity to bind other molecule of the substrate, which once bound increases the affinity for the third subunit and goes on. This increases affinity of the enzyme toward substrate forms a Sigmoid (S) curve which is simmilar to the following curve.

The example of cooperative binding is oxygen binding to Hemoglobin. Here, after the binding of one oxygen (as a ligand) to the firstunit of Hemoglobin, the newly formed 2nd unit has an increased tendency to bind other molecule of oxygen, again the third subunit also enhanced tendency to bind oxygen. Therefore the rate of reaction increases with increasing concentration of oxygen.