The Reaction of Chicken Ovalbumin with Homologous Antibody in the Region of Antibody Excess

Abstract

A pronounced decrease in the amount of precipitation in the region of antibody excess has been observed in the reaction of chicken ovalbumin with the concentrated globulin fraction of its homologous rabbit antiserum. A significant decrease was observed at a molar ratio of antibody to antigen of about 50:1, with almost complete inhibition at a ratio of 300:1. The results were confirmed with radioiodinated antigen; a much larger proportion of the antigen appeared in the supernatant in the prozone. The amount of precipitate formed is dependent on the method used for mixing the two reactants. For maximum inhibition by excess antibody, it is necessary to add the antigen to antibody and to stir during the addition, so as to maintain constantly a high antibody to antigen ratio. A large effect of order of addition was observed; the inhibiting effect of excess antibody was greatly decreased when antibody was added slowly to antigen so that the proportions in the mixture passed through the equivalence zone. Attempts to dissolve precipitates by extraction with excess antibody at 0° or 56°C have been unsuccessful. A high free energy of activation in the transformation of precipitate to soluble complexes is indicated.