Figure 4.

An operational model of allosterism to quantify CaSR agonist, PAM, and NAM actions. Endogenous CaSR agonists such as Ca²⁺_o bind with a mean equilibrium dissociation constant, K_A, to multiple sites. When the receptor is occupied by an agonist, the agonist stimulates a response, depicted by an operational measure of efficacy, τ_A. Allosteric modulators may alter the equilibrium dissociation constant of the agonist via a cooperativity factor, α, or alter the efficacy of the orthosteric agonist via a scaling factor, β. Allosteric modulators may also have their own efficacy, τ_B.