Antibody Affinity

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Abstract
Rabbit antibody of restricted heterogeneity induced by a lactoside determinant has been specifically purified and further fractionated into functionally homogeneous populations. These preparations have been used to evaluate the association constants for binding to the bacteriophage φX174 to which had been coupled multiple lactoside groups. The constants were obtained from equilibrium neutralization experiments and compared to the association constants for the binding of a monovalent lactosyl-containing ligand. The central finding is that the constant for the binding of the antibody to bacteriophage is greater by a factor of 104 than that for the monovalent ligand. As previously suggested in another system, this effect is attributed to bivalent interaction and serves to establish the generality of the enhancement phenomenon. The use of functionally homogeneous antibody precluded the possibility that selection of high-affinity antibody was responsible for enhancement. The issue of the number of critical sites available for neutralization on the conjugated bacteriophage was clarified by comparison of the observed reactivation kinetics with the behavior predicted from a model system. It was inferred that the number of such sites did not exceed two and could be one. Thus the process of neutralization and reactivation can be adequately described by an analysis based on single-site kinetics.

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