Determination of Antibody-Hapten Equilibrium Constants by an Ammonium Sulfate Precipitation Technique

Abstract

The determination of the equilibrium constant of antibody-hapten interactions has led to important insights into the specificity and structure of antibodies (1) and into the nature and control of the immune response (2). The techniques presently used for measuring this constant all have certain disadvantages. Equilibrium dialysis (3), which must be regarded as the primary method, is relatively tedious to perform whereas other techniques, such as fluorescence quenching (4), require the use of purified antibody and of expensive equipment. We now report the satisfactory determination of the average intrinsic association constant (K₀) of hapten-antibody interaction on the basis of data obtained by precipitating antibody-hapten complexes with ammonium sulfate solutions. This represents an extension of the well-known Farr technique (5), which has previously been used to estimate the avidity of anti-bovine serum albumin antibody.