A monoclonal antibody recognizing the FAD-binding site of 4-aminobenzoate hydroxylase from Agaricus bisporus.

A monoclonal antibody against 4-aminobenzoate hydroxylase (EC 1.14.13.27) from Agaricus bisporus, a common edible mushroom, has been produced by the fusion of BALB/c mouse spleen cells immunized with the denatured enzyme and P3x63Ag8U1 myeloma cells in order to locate and characterize the catalytic site of the enzyme. The monoclonal antibody immunoblotted the enzyme and immunoprecipitated its apoenzyme. The immunoprecipitation was inhibited in the presence of FAD, and the monoclonal antibody competitively inhibited the binding of FAD to the apoenzyme. The monoclonal antibody, therefore, recognizes the FAD-binding site of 4-aminobenzoate hydroxylase. Interestingly, it was shown that the monoclonal antibody was cross-reactive with FAD-dependent enzymes such as salicylate hydroxylase (EC 1.14.13.1) and D-amino acid oxidase (EC 1.4.3.3), and that it was specific for the FAD-binding sites of these enzymes. This fact suggests that these FAD-dependent enzymes have immunologically similar structures on their FAD-binding sites.