Receptor (biochemistry) - Binding and Activation

Binding and Activation

Ligand binding is an equilibrium process. Ligands bind to receptors and dissociate from them according to the law of mass action.

(the brackets stand for concentrations)

One measure of how well a molecule fits a receptor is the binding affinity, which is inversely related to the dissociation constant K_d. A good fit corresponds with high affinity and low K_d. The final biological response (e.g. second messenger cascade, muscle contraction), is only achieved after a significant number of receptors are activated.

The receptor-ligand affinity is greater than enzyme-substrate affinity. Whilst both interactions are specific and reversible, there is no chemical modification of the ligand as seen with the substrate upon binding to its enzyme.