Question

Protein P binds to ligand L with a Kd of 10-6 M. Protein Q binds to ligand L with a Kd of 10-9 M. Which protein has higher affinity for ligand L and why? Find out the corresponding Ka values for both the proteins.

Answer 1

Protein Q has a higher affinity for ligand L because its Kd value is lower than that of Protein P. Kd is the dissociation constant, which is the concentration of free ligand at which half of the protein-ligand complex is dissociated. A lower Kd value indicates a higher affinity for the ligand.

The Ka value is the association constant, which is the reciprocal of the dissociation constant. It represents the strength of the interaction between the protein and the ligand. The Ka value can be calculated using the following formula:

Ka = 1/Kd

Therefore, the Ka value for Protein P would be:

Ka = 1/10^-6 M = 10^6 M^-1

And the Ka value for Protein Q would be:

Ka = 1/10^-9 M = 10^9 M^-1

Protein Q has a higher Ka value, indicating a stronger interaction with the ligand.