Two simple reaction schemes. Panel A. The cyclic two-state model, cTSM, with selection and induction arrows indicating two separate but simultaneous pathways from an inactive and non-liganded receptor conformation R to an active and agonist S liganded receptor conformation R*S. A
s is an equilibrium association constant for S, L is a conformational efficacy constant for non-bound receptors, and parameter a is an efficacy constant for ligand bound receptor conformations from RS to R*S. Panel B. The ternary-complex model, TCM, in which symbol M represents the term and concentration for an additional alloster ligand. A
m is an equilibrium association constant for M, and parameter c is a cooperativity coefficient for two-ligand binding.