Irreversible inhibition of a monoclonal antibody by a nitrophenyl ester

TEPC-15 is a phosphorylcholine-binding mouse myeloma protein which reacts with an ester-containing phosphorylcholine, the p-nitrophenyl ester of 6-(phosphorylcholine)hexanoic acid (PEPCH). The rate of nitrophenolate release mediated by the antibody is pH-dependent and increases with increasing pH. The antibody becomes inactive during the reaction with the ester. The inactive antibody is not reactivated even after treatment with hydroxylamine. Antibody activity is associated with the Fab' fragment. These observations together with the pH profile of the reaction suggest that the ester acylates a lysine side chain near the antibody-binding site.