Concept #1: Protein-Ligand Equilibrium Constants

Concept #2: Protein-Ligand Dissociation Constant

Practice: Protein A has a binding site for ligand X with a K d of 54 mM. Protein B has a binding site for ligand X with a Kd of 58 mM. Answer the following questions based on this information:

A) Which protein has a stronger affinity for ligand X?

B) Convert the Kd to Ka for both proteins.

Ka for Protein A: __________ 

Ka for Protein B: __________

Practice: You prepare a solution of protein and its ligand where the initial concentrations are [P] = 10 mM and  [L] = 10 mM. At equilibrium you measure the concentration of the complex [PL] = 5 mM. If the protein-ligand reaction can be represented by P + L ⇌ PL, what is the Kd of the reaction under these conditions?