Antibody-hapten interactions electrostatic interaction

Most of the agrochemicals are relatively small molecules and the antibodies produced in animals may, by comparison, be fairly uniform with respect to complementarity. When antisera to haptens are diluted sufficiently so as to favor interaction with the most avid antibodies, the Scatchard plots often are indicative of fairly homogeneous populations of antibodies. Their affinity constants could reach as high as 1012 M 1. The intermolecular forces involved in the binding of antigens to antibody include hydrophobic, Van der Waals, electrostatic and hydrogen binding (28-31). 

The binding forces are electrostatic attractions between sites with opposite charges such as -NH3 carried by a lysine residue and a carboxylate, van der Waals forces, and hydrogen bonds. It is predicted that the first two types of bonds, which increase rapidly as the distances decrease, will be all the more efficient as the complementarity is better. The expression hydrophobic interactions is used because an exact fit drives away water molecules present close to the hydrophobic residues such as valine, leucine, isoleucine, etc. This concept, developed further in Chapter 11, implies that a decrease in surface contact with water is in itself a stabilizing factor. All these forces are reversible. When the hapten-antibody complex in solution is introduced into a dialysis bag, only the hapten can cross over the membrane, and its elimination from the interior bag causes complete dissociation of the complex through equilibrium displacement. 

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