A Homologous Series of Affinity Labeling Reagents and Their Use in the Study of Antibody Binding Sites

A series of new radioactive affinity-labeling reagents for anti-DNP antibodies was synthesized. The chemically reactive group in these reagents (bromoacetyl derivatives of DNP haptens) is situated at an increasing distance from the DNP ring. This series thus provides a useful tool for the systematic mapping of antibody binding sites. Each of the reagents reacts specifically with the combining site of anti-DNP antibodies as shown by a variety of chemical and physicochemical criteria, such as stoichiometric bonding to a specific antibody only, and protection of the site by DNP haptens. Using a homologous series of reagents it was possible to show that both tyrosine and lysine become labeled and are apparently present at the combining sites of goat anti-DNP antibodies. The distribution of the label between these two amino acids was different with antibodies from different animals and is probably an individual trait of tne animal.