E10 Receptor-ligand kinetics

Title

The activation of membrane receptors (the same R of E04, now treated generally) by neurotransmitters, hormones or drugs is governed by the law of mass action: the free ligand L binds reversibly to the free receptor R to form the LR complex, with association and dissociation constants that define the affinity of the system (dissociation constant K_D). At equilibrium, the fraction of occupied receptors follows a simple hyperbolic relationship or, when there is cooperative binding between multiple sites, a sigmoid Hill relationship characterized by the Hill coefficient n_H. Conservation of the total receptor links the free and bound form at all times. Many receptors, in addition, transition to a desensitized state after prolonged exposure to the ligand, reducing the response despite sustained occupation. When two ligands compete for the same binding site, their kinetics are coupled through the shared free receptor, and the resulting functional response is usually summarized by an Emax-type dose-response curve.

ID:4268