Consider a monomeric protein, P, that can bind to two different ligands, A and B. The binding sites for the two ligands overlap, such that the second ligand cannot bind to a protein molecule already complexed with the first ligand, and vice versa.

a) Derive an expression for the equilibrium fraction of protein complexed with the first ligand when both ligands are present. How does the presence of the second ligand affect protein complexation with A? What happens to the fraction bound when the KD,B is very high?