Specificity of antigenic recognition of antibody heavy chain

Abstract

The specificity of antigenic recognition of the component chains of purified dinitrophenyl and trinitrophenyl antibodies was examined. Heavy chains were rendered soluble at neutral pH, either by prior reaction of the parent antibodies with D,L-alanine N-carboxy anhydride, or by mixing heavy chain with light chain of non-specific IgG. The degree of homologous light chain contamination of these heavy chain preparations was found to be less than 2%, either by immune precipitation, or by end-group analysis. Association constants of the heavy chains of both antibodies with several closely related haptenes were measured by fluorescence quenching. Heavy chains differentiated among these haptenes in the same manner as the parent antibodies, though considerable binding affinity was lost. When specific homologous light chains were added to the heavy chain preparations, association constants were increased, but without change in relative selectivity. Binding activity of light chains alone could not be measured. The heavy chain, then, appears to bear the specificity of its parent molecule. Whether or not homologous light chain contributes additional specific information with respect to antigenic recognition or simply plays a non-specific modulating role cannot be answered from these experiments.