Affinity Diffusion. I. Method for Measuring Dissociation Constants of Precipitating Antibodies

Abstract

Dissociation constants (K_d) of antigen-antibody reactions can be obtained from the rates (measured by the progression of the precipitate vs. time) with which antigens diffuse into antibody-containing gels, as a function of antibody-concentration. A bovine serum albumin vs. rabbit anti-bovine serum albumin system was studied with whole antiserum and with its purified IgG fraction. A value was found for K_d of ≈1.0 × 10⁻⁵ moles per liter. It is noteworthy that in monodimensional single diffusion gel precipitation systems of this type, the rate of progression of the precipitate front is significantly faster than the molecular diffusion coefficient of the antigen.