Effects of the extent of DNP substitution on the apparent affinity constant and cooperation between sites in the reactions od dinitrophenylated human serum albumin with anti-DNP and anti-HSA antibodies coupled to agarose

Increments in the extent of dinitrophenyl (DNP)^* substitution of human serum albumin (HSA) increases the apparent affinity constant of its reaction with anti-DNP antibodies coupled to agarose and decreases that of its reaction with anti-HSA antibodies also fixed to the same solid phase. An ascending limb of the Scatchard plot in the low levels of bound ligand is described and is shown to be also dependent of the degree of DNP substitution of the antigen. Resulta are discussed as indicative of a probabilistic effect of the antigens' valence on the apparent affinity constant for antibodies coupled to agarose while the ascending limb of the Scatchard plots as compatible with cooperation between antibody active sites.