Influence of ligand valency on ligand-influenced monomer-dimer equilibrium systems and biological control mechanisms.

Two specific ligand-influenced monomer-dimer equilibrium systems are discussed. Each has a ligand-to-dimer subunit ratio of 0.5. Equilibrium characteristics of the system are described in terms of the effect of a bivalent ligand on both experimental and theoretical analysis. It is shown that Hill expressions need to be modified for multivalent ligand systems, and care is needed in equilibrium parameter determination. Some unique properties of these systems are retained, yet others are altered in the presence of a multivalent ligand. A suggestion as to the minimum amount of information needed to describe completely a ligand-influenced monomer-dimer system is given. The estrogen-receptor system is presented as an attractive biological model for both theoretical and experimental study of ligand-influenced polymerizing systems and their role in cellular control requirements.