title: General thermodynamic considerations of receptor interactions.
abstract: Assuming that the biological response is directly proportional to the fractional degree of receptor occupancy, the mathematical relationships between free ligand concentration, receptor occupation and biological activity are developed for a number of equilibrium models. The models considered include simple 1:1 binding with and without conformational changes in the receptor, the coupled binding of two distinct effectors to a single macromolecule, and a system involving indirect coupling between two effectors that bind to two distinct components of the receptor system. This latter model is elaborated into the concept of a domain of receptor-enzyme pairs such that occupation of a single receptor may activate the entire domain of enzymes. This model can explain discrepancies between activation and binding isotherms as has been found with some beta-adrenergic agonist-sensitive adenylate cyclase systems.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D006150:Guanine Nucleotides / Q000502:physiology; D007700:Kinetics; D008024:Ligands; D008954:Models, Biological; D011487:Protein Conformation; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D011955:Receptors, Drug / Q000502:physiology*; D013816:Thermodynamics
chemical_list: D006150:Guanine Nucleotides; D008024:Ligands; D011943:Receptors, Adrenergic, beta; D011955:Receptors, Drug; D000262:Adenylyl Cyclases