Effect of monoclonal antibodies against peroxidase on peroxidase-catalyzed oxidation of o-phenylenediamine

Horseradish peroxidase (HRP)-specific monoclonal antibodies (MABs) 2C, 9D, and 9F, interacting with domain I of the enzyme, have been shown to activate HRP in the reaction of o-phenylenediamine (OPD) oxidation at moderate H2O2 concentrations (<10 mM). In contrast, the monoclonal antibody 3E, interacting with domain II, inhibited the oxidation of OPD over a broad range of H2O2 concentrations. HRP-specific polyclonal antibodies (PABs) were inhibitory irrespective of H2O2 Concentration. Similar effects were observed when OPD was oxidized by a hydrophobic conjugate of HRP with nine molecules of cortisol. Possible mechanisms underlying the activation and inhibition of the enzyme are discussed.