Figure 4

The kinetic scheme for the full cooperative model. Model 3: This model provides the most realistic description of the Ca²⁺-CaM-target protein complex assembly. The model assumes that both the N- and C-terminal contain two cooperatively bound EF-hand Ca²⁺-binding pairs. These sites cooperatively influence each other only and do not have any effect on Ca²⁺ binding on the other terminal. This cooperative interaction is symmetrical, in the sense that any unoccupied site in the terminal increases the affinity of its neighbour in the same way that it would be influenced by its neighbour if its neighbour bound a Ca²⁺ ion first. Both the "original" and cooperatively influenced dissociation constants are dependent on whether or not CaM is bound to a target protein.