Specificity of antibodies: primary structural basis of hapten binding.

The primiary structure of the 83 residues of the NH(2)-terminus of the V(II), region was determined for each of three different antibodies to hapten which were produced in inbred guinea pigs. Each antibody had a different and distinctive primary structure within each of the two "hypervariable" regions (Hv1 and Hv2) included in the analyzed part of the variable region of the heavy chain. The sequences of Hvl and Hv2 in the three antibodies were either unique or of restricted variability compared with those of "normnal" immunoglobulin G2. Further implication of Hv1 and Hv2 in contributing to ligand-binding specificity of antibodies came from the placement of residues modified by affinity labeling reagents in these hypervariable regions.