Search

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.

SummaryThe activation of Hageman factor (factor XII) by ellagic acid may involve a conformational change in which at least some of its hydrophobic regions, previously buried, are exposed to the surrounding environment. The fluorescent probe, l,6-diphenyl-l,3,5-hexatriene (DPH), when added to a solution of ellagic acid-activated Hageman factor, displayed substantially more fluorescence compared to solutions of the probe and the unactivated form of the protein. These studies imply that the hydrophobic regions of activated Hageman factor are exposed in such a way that the DPH probe has easy access to the hy-drophobic environment to which it binds.This work was supported in part by Research Grants HL 15195 and HL 01661 from the National Heart, Lung and Blood Institute, The National Institutes of Health, U. S. Public Health Service, and in part by grants from the American Heart Association and its Northeast Ohio Affiliate. Ms. Janet Shlaes provided invaluable technical help.