Figure 4. Scheme describing the concerted (MWC) and sequential (KNF) allosteric models for a tetramer.

According to the concerted model, the oligomer in its apo state is in equilibrium between low (T) and high (R) affinity states for the ligand (L = [R]/[T]). In the case of the concerted model with exclusive binding of the ligand to the R state (A), the values of the intrinsic binding constants corresponding to all the successive binding steps will be the same except that of the first site which will differ by a factor of L/(1+L). In the case of the concerted model with nonexclusive binding of the ligand to both the T and R states (B), the values of the intrinsic binding constants corresponding to the successive binding steps will all differ from each other but they will form a series that can be expressed as a function of L and the respective ligand binding constants of the T and R states, K_T and K_R. In the case of the sequential model (C), a simple relationship between the values of the N binding constants is not necessarily expected.