Oxidoreductase activity of multifunctional monoclonal antibody B13-DE1

The monoclonal antibody B13-DE1 binds fluorescein, several fluorescein derivatives, and three peptide mimotopes. Our results revealed that this antibody also catalyzed the redox reaction of resazurin to resorufin, which are both structurally related to fluorescein. By using sodium sulfite as a reducing agent, the antibody B13-DE1 lowered the activation energy of this reaction. The Michaelis-Menten constant and turnover number of the catalyzed reaction were determined as 4.2 µmol/l and 0.0056 s(-1) , respectively. Because the results showed that fluorescein inhibited the catalytic activity of the antibody, we assume that the antigen-binding site and the catalytic active site are identical.