PROTEOLYTIC ACTIVITY OF AN ANTIBODY LIGHT-CHAIN

The light chain (L chain) of a mAb raised against unactivated vasoacti ve intestinal peptide (VIP) hydrolyzed this peptide, whereas the heavy chain (H chain) and an irrelevant L chain were without activity. The reaction kinetics were consistent with efficient substrate recognition by the anti-VIP L chain compared with conventional proteases. The L c hain cleaved four peptide bonds clustered between residues 16 and 21 i n VIP. Mixtures of the L chain with its H chain partner displayed redu ced hydrolytic activity compared with the free L chain, suggesting tha t the H chain is a modulator of the catalytic activity. These observat ions suggest: 1) the immune system can generate catalytic sites in the L chain subunit of Abs found in response to polypeptide Ags,and 2) fr ee L chains found in vivo could display an Ag-specific catalytic funct ion.