Antigenic structure of sperm whale myoglobin. II. Characterization of antibodies preferentially reactive with peptides arising in response to immunization with the native protein.

The antigenicity of peptide fragments derived from CNBr-cleaved sperm whale Mb has been tested in competitive inhibition assays. These peptides appeared to be very poor inhibitors in a reaction involving radiolabeled sperm whale Mb with antipeptide antibodies, requiring about 10(4)-fold excess of peptides to achieve the same level of inhibition as cold native Mb. However, cold peptides competed much better with radiolabeled peptides for antibody binding than the native protein. These antibodies, preferentially reactive with peptides, originated from sera of animals immunized with the native molecule. This indicates heterogeneity of the antibodies produced against Mb and suggests the presence of diverse antibody subpopulations reactive with different antigenic forms of the protein. Results presented in this paper illustrate that competitive radioimmunoassays preferentially measure antibodies to the radiolabeled species, and this phenomenon can be used to demonstrate distinct populations among antibodies isolated to a single peptide.