ABSTRACT
The lifetime of a receptor-ligand complex, once it forms, is not a definite quantity. The complex may last a relatively short time or it may last a relatively long time. Even though we cannot assign a definite value to the lifetime of the glove-ball (receptor-ligand) complex, we can observe that it rarely lasts for less than some short but measurable time and it rarely lasts for more than some measurable, longer time. There are generally two things we want to know about a receptor: the affinity of the receptor and ligand for one another, and the number of receptor molecules (or more generally, the number of ligand binding sites) present. Common laboratory practice is to mix the receptors and ligands in different ratios and measure the amount of RL complex at equilibrium. Generally, this is done by holding the receptor concentration constant and varying the ligand concentration.
