Ligand binding reaction association/dissociation constant

The equilibrium association constant for this reaction is defined as ki/kj and provides an index of the affinity between the binding sites and the ligand. The inverse of the association constant (1/ a) is the equilibrium dissociation constant for the drug-protein complex ... 

In this equation, is the association equilibrium constant for the binding of A with L, is the association rate constant for this reaction, and is the corresponding dissociation rate constant. The terms [A], L and A-L represent the concentration of the analyte in solution at equilibrium and the surface concentrations of the ligand and analyte-ligand complex under these same conditions. 

Figure 4.24 Model for ligand binding to cell surface receptors. A single cell with R receptors is held in medium containing ligand at bulk concentrations Cl o- The system is characterized by rate constants for the intrinsic rate of association and dissociation (kon and kon), diffusion of ligand to the cell surface (D), and rate constants for the overall association and dissociation reactions (k[ and k ).

If K is the microscopic equilibrium constant for the association of the monotopic ligand A with B, the stepwise constants are K = 3K Ki =K Ks= K/3. The statistical factors are easily understood in the first equilibrium, three equivalent binding sites A are available for binding in the second, two equivalent binding sites A are available in the forward reaction but two equivalent bonds A—B can dissociate in the reverse reaction in the third, there are three equivalent bonds A—B which can dissociate in the reverse reaction. In general, for the interaction of a symmetrical m-topic ligand with a monotopic metalloporphyrin, the stepwise constants K( are given by Eq. 2, from which Eq. 3 is easily derived [20,29-31]. 

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