Figure 3.

Partial activation of a receptor by an agonist. The agonist stabilizes a partially active form of the receptor (R^*) so that the measured agonist affinity is not equal to the ground-state affinity. Equilibrium association constants for agonist binding (K_R, K_R^*) are shown and L is defined as [R^*]/[R]. We can define a factor β for the effect of the R/R^* transition on agonist binding so that K_R^*=βK_R. If ligand-binding studies are applied to this scheme, the experimentally determined dissociation constant of an agonist (K_obs) is given by: K_obs=K_A ((1+L)/(1+βL)).