Identification of an Antigenic Determinant on Anionic Peanut Peroxidase by Monoclonal Antibodies

Two monoclonal antibodies (46–12-C12 and 23–6-C12) raised against anionic peanut peroxidase were found to have independent epitope sites. These topographic sites were found to be located within a tryptic glycopeptide (Atgp) from the anionic isozyme by both indirect and non-competive ELISA and Western blotting. The Atgp has a Mr equal to 11 000 of which 70% is carbohydrate and the peptide is probably highly hydrophobic as determined by its high RF (0.83) value and the amino acid composition. McAb 23–6-C12 recognized a contiguous epitope which encompassed also the sole N-linked oligosaccharide on the anionic isozyme. That the monoclonal antibody also recognized the oligosaccharide on the α-amylase, β-glucosidase, acid phosphatase, and horse-radish peroxidase may be related to similarities in sugars. Sugar removal from the Atgp or from the cross-reactive peptide of enzymes caused loss of antibody affinity. The monoclonal antibody 46–12-C12 recognized specifically a conformational epitope near the region of the cysteine, tryptophane and methionine residue on Atgp. Digestion of the anionic isozyme by trypsin resulted in a 40-fold loss of affinity with this monoclonal antibody. Moreover, treatment of the Atgp with performic acid or trifluoromethane sulphonic acid caused a loss of affinity between the treated Atgp and this monoclonal antibody.