THE IMPORTANCE OF ELECTROSTATIC INTERACTIONS IN THE BINDING OF PARAQUAT TO ITS ELICITED MONOCLONAL-ANTIBODY

In this study the pH-dependent interactions interactions between a paraquat-specific murine monoclonal antibody and two antigens: paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride), and a p-nitrophenol analogue (1-(N-methyl-4,4'-bipyridinium)-1-(2-hydroxy-5-nitrophenyl)methane dichloride; PQNP) were determined by ELISA. In each case the KAS-pH profile reflected the titration of a single amino acid residue. pK'a values derived from these plots were 8.90 (paraquat) and 8.13 (PQNP). Increasing pH led to a significant increase in the association constant for each antibody complex. A spectrophotometric titration of PQNP in the presence and absence of excess antibody indicated the presence of another charged amino acid residue at the binding site, which could be assigned as a carboxylic acid. From these studies, a model for paraquat-antibody binding has been proposed. © 1990.