Vasoactive intestinal peptide hydrolysis by antibody light chains.

This paper describes evidence for hydrolysis of a neuropeptide, vasoactive intestinal peptide (VIP), by light chains purified from the IgG of a human subject positive for VIP binding antibodies. Purified IgG was digested with papain, resultant fragment antigen binding (Fab) fragments were reduced with 2-mercaptoethanol and alkylated with iodoacetamide, and light chains were purified by chromatography on immobilized antibodies to light chains and immobilized antibodies to heavy chains. Non-immunoglobulin components were undetectable in the light chain preparation, judged by sodium dodecyl sulfate-electrophoresis and Western blotting with anti-heavy and anti-light chain antibodies. The light chains hydrolyzed VIP with specific activity 32-fold greater than that of Fab, the pH optimum for light chain-mediated VIP hydrolysis was 7.0-7.5, and the hydrolytic activity was saturable (Vmax, 0.19 pmol/min/microgram light chains; substrate concentration at Vmax/2,380 nM).