Kinetics of haloperidol binding to monoclonal antibodies as measured by direct fluorescence quenching

Monoclonal antibodies which bind small neurogenic ligands may mimic certain aspects of the stereospecific binding present in the natural biological receptor, and may prove useful in designing engineered protein receptors, provided their interactions are correctly understood. We report here the kinetic and equilibrium characteristics of ligand-antibody complexes of haloperidol, a dopaminergic antagonist, with three of its monoclonal antibodies as studied by fluorescence quenching techniques. These antibodies possessed moderate to high affinity constants, ranging from 10(5) to 10(9) M-1, and caused fluorescence quenching of a fluorescein-labeled haloperidol as well as quenching (40-60%) of the internal tryptophan fluorescence. The dissociation rates of the ligand from the complexes were measured at different conditions of temperature, pH and ionic strength. The results provide important information regarding the kinetic and thermodynamic parameters of the binding pockets of these antibodies.