Association constants, receptor-ligand interaction

Resonant mirror biosensing is a superb technique for the analysis of receptor-ligand interactions in real time. Therefore, association constants may be determined directly from kinetic constants This may sound a little strange, but let us consider the binding equilibrium shown in Scheme 7.4. By definition, equilibrium is reached when the rate of association (M s ) of receptor with ligand is equalled by the rate of receptor-ligand complex dissociation diss (s )- Hence... 

In contrast, reaction of ligand 72 with 4,4 -biphenyldiboronic acid has been successful and diboronate 73 is obtained in yields of 33%. This complex acts as a receptor for the paraquat dication forming a 1 1 complex with an association constant of 320 in acetone. The intermolecular forces responsible for the complexation are ion-dipole stabilization between the dative N B dipoles and the two cationic centers in paraquat, attractive tz-tz interactions between... 

The data below describe the binding of ligand L to the oligomeric receptor R (100 juM). Create a script hie and data hie to evaluate the association constant and the number of equivalent sites. Calculate Hill s interaction coefficient by perform regression analysis. 

Figure 7.15 Ideal binding isotherms, (a) Classical hyperbolic binding isotherm obtained by plotting values of S against [L]. (b) Classical semi-log plot obtained by plotting values of S against log[L]. Appearance of sigmoidal shape implies that binding interactions between ligand and receptor are >70% saturated and binding data are therefore appropriate to derive accurate association constant Ka or dissociation constant Aj values.

In this reaction the ligand and the receptor associate, so this is called an association process (or interaction) and its equilibrium constant is an association constant, or Ka. 

In the case for a bivalent interaction, Lees proposed an extension of this model by assuming that the bivalent association constant can be expressed as three related association constants K, K2, and K-iP Each equilibrium constant is derived on the basis of certain approximations such as the number of possible permutations assumed in receptor-ligand site association, monovalent binding (each monomer of the bivalent ligand is capable of binding to one receptor), and effective concentration of bound divalent ligand. An overall divalent association constant, which provides an estimate of the enhancement factor of divalent association, is obtained as a product of the three equilibrium constants as shown in (5). The refinement in p that is afforded from Lees treatment is shown in (6). 

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