Dimerization of an antigenic peptide leads to strong interaction with its antibody

A sequential epitope reacting with a monoclonal antibody against Panulirus interruptus hemocyanin was localized in the C-terminal CNBr peptide. As the antibody reacted with about equal affinity with different subunits of this and with hemocyanin from another spiny lobster, Palinurus vulgaris, the epitope was assigned to a conserved sequence region. The CNBr peptide, which was linked to another peptide via a disulfide bridge, was reduced and reoxidized. As a result, not the heterodimer but only the two disulfide-linked homodimers were formed. The dimeric C-terminal peptide had a much higher affinity for the monoclonal antibody than the monomeric peptide. This may be explained by the presence of two independent mobile interaction sites in each of the two reacting molecules.