Simulations from four sub-models of the ternary-complex model, TCM. For sub-model definitions see Table 2. Parameters A
s and A
m, equilibrium association constants for ligands S and M, are kept at unity. Parameter c, the cooperativity constant for binding, is varied by a factor 103 in three steps for each sub-model as indicated in the panels. Red curves indicate orthoster concentration-response curves in the absence of an alloster. In all panels the alloster M concentration is varied in four steps: in panels A-I by a factor 102 from 1x10-2 to 1x104; in panels G-K by a factor 10 from 1x10-2 to 1x101 and in panel L by a factor 102 from 1x10-3 to 1x103. Green curves with circles show the actual EC50 and the black circle represents the position of a limiting EC50 for M → ∞.