The effect of limited nitration on antibodies to dinitrophenyl group

Abstract

The studies of Singer and his colleagues, using aftinity labelling, have demonstrated that tyrosine residues are present in the combining sites of antibodies of a fairly wide range of specificities, including antibodies to the 2,4dinitrophenyl (DNP) group [ 1,2] . Iodination studies also inferred tyrosine to be present in the combining site of different antibodies [3,4]. However, in the iodination experiments a substantial decrease in antibody activity was achieved only when a relatively large number of iodine (about 30 atoms per molecule) have been incorporated into antibody. Tetranitromethane (TNM) was recently introduced as a mild specific reagent for nitration of tyrosyl residues of proteins [5] and it has been demonstrated that in certain cases TNM reacts selectively with unique tyrosyl residues [6,7]. We report here the effect of TNM on anti-DNP antibodies. Nitration of an average of two tyrosyl residues per anti-DNP molecule destroyed about 50% of the antibody combining sites. In addition the precipitation of the nitrated antibody with DNP-ovalbumin became dependent on the ionization of the nitrotyrosyl residues. Both effects could be prevented by the presence of hapten during the nitraItion.