Specific Cation Effects with Antibody to a Hapten with a Positive Charge

The binding of homologous hapten by antibody to the positively charged p-azophenyltrimethylammonium ion was found to be decreased by inorganic cations but not by anions. This appears due to the competition of the cations with the hapten for the negative charge in the specific site of the antibody molecule. The order of effect for singly charged cations is Cs+ > Rb+ > NH+4 ≥ K+ > Na+ ≥ Li+, which is in the order of the ionic radii and the inverse order of the radius of the hydrated ions. For doubly charged cations the order is Ba++ > Ca++ > Mg++.