NONPRECIPITATING PIG ANTI-DINITROPHENYL ANTIBODY - FACTORS INFLUENCING THE CONVERSION INTO PRECIPITATING ANTIBODY

A high affinity nonprecipitating anti‐2,4‐dinitrophenyl (DNP) IgG antibody constitutes a major fraction of circulating anti‐DNP antibodies at the decline of the anti‐ DNP antibody response in pigs. The purified nonprecipitating antibody forms exclusively soluble complexes with DNP‐PSA (pig serum albumin) or DNP‐PGG (pig IgG). The binding sites are accessible to large ligands; one antibody molecule can combine with two molecules of DNP‐PSA simultaneoulsy. The formation of complexes with DNP‐PSA was studied in various media. No precipitate was formed in saline, in 0.9 M or 0.05 M sodium chloride, in 0.5 M potassium thiocyanate and in several nonionic detergent solutions (0.5% and 1%). Normal pig or guinea pig sera were found to contain a factor, removable by an antigen‐antibody precipitate that caused a partial precipitation of the complexes. A mild alteration of the integrity of the antibody molecule by cleavage of interchain disulfide bonds did not affect the nonprecipitating character of the antibody. In media containing hydrophilic polymers, i.e. various dextrans, polyethylene glycols or a soluble polyamide (poly‐α,β5‐[N(2‐hydroxyethyl)‐DL‐aspartamide]), a functional conversion occurred; the antibody behaved like a precipitin. The precipitate with DNP‐PSA could not be resolubilized upon removal of the polymer by washing. The magnitude of the functional conversion depended on the concentration of the polymer and on its molecular weight, larger molecules being more effective. The effect of the hydrophilic polymers could be potentiated by replacing water in the solvent partly by deuterium oxide. The findings are compatible with a notion, that in polymer‐containing media the nonprecipitating antibody acquires a conformation functionally equivalent to the conformation of a precipitating antibody and that the altered conformation is stabilized by the lattice of the precipitate with DNP‐PSA. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim