ANTIGEN RECOGNITION BY AN ANTIBODY LIGHT-CHAIN

A monoclonal antibody to vasoactive intestinal polypeptide (VIP) was r educed and alkylated and its light and heavy chains were purified by d enaturing gel filtration. Following renaturation, the light chain disp layed sequence-specific binding of VIP. The specific VIP binding activ ity of several fractions spanning the light chain peak recovered from the gel filtration column was constant, the light chain was electropho retically homogeneous, the VIP binding activity was precipitated by an tilight chain antibody but not anti-heavy chain antibody and the activ ity remained associated with a light chain fraction recovered by resol utive chromatography on a hydroxylapatite column. N-terminal amino aci d sequencing of the light and heavy chain, fractions confirmed the pur ity of these proteins and suggested that the V(L) and V(H) regions bel onged to kappa-family II and gamma-family III, respectively. The VIP-b inding affinity of the light chain was only 5-fold lower than that of the parent antibody and the light chain did not bind unrelated peptide s. These observations suggest that light chains display structural cha racteristics necessary for high affinity antigen binding.