Three-site allosteric binding model. (A) State diagram in which symbols Rijk designate states with i, j, and k ligands bound to sites I, II, and III (i, j, k = 0 or 1). KI, KII, and KIII represent microscopic equilibrium association constants for sites I–III. Conditional cooperativity factors fJ(K,L) represent fold change in binding to site J given that sites K and L are occupied. (B) Expressions for state populations for model in A and relation between model parameters and fit parameters: p1 = KI + KII + KIII, p2 = fI(II) KI KII + fI(III) KI KIII + fII(III) KII KIII, and p3 = fII(III) fI(II,III) KI KII KIII. States and expressions are color coded black, red, blue, and purple for zero, one, two, and three bound ligands, respectively.
