Scheme 1.
The selective precipitation proteins with oligovalent ligands. The dissociation constant (Kd) dictates the formation and stability of a bivalent protein-ligand aggregate, in which a bivalent ligand of known binding affinity is introduced into a solution containing the protein. The Kd of the monovalent and bivalent complex is assumed to be the same in this system. The increase in mass (and volume) of the aggregates, in solution, results in the decreased solubility of the protein(s), and promote precipitation.