Affinity labeling of anti-dinitrophenyl antibodies with bromoacetyl derivatives of homologous haptens

Affinity labeling (1) was used extensively by Singer and his colleagues to study the combining sites of antibodies (2). In these studies diazonium affinity labeling reagents were used and in most cases the reagent formed an azo linkage to tyrosine residues at the combining site (2). In an attempt to develop affinity labeling reagents with a reactive group of different chemical specificity we prepared the bromoacetyl derivatives of some dinitrophenyl (DNP) haptens and tested their specific covalent binding to anti-DNP antibodies. We report here the affinity labeling of anti-DNP antibodies by α-N-bromoacetyl, ε, N-DNP-L-lysine and by N-bromoacetyl, N¹-DNP-ethylene diamine. Both reagents are very specific but differ in their efficiency of labeling. More than 95% of the labeling was due to O-alkylation of tyrosine residue in the antibody combining site and after acid hydrolysis O-carboxymethyltyrosine was identified as the labeled residue.