| Affiliation: | 1. Department of Biology and Biotechnology “Lazzaro Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy These authors contributed equally to this work.;2. Department of Drug Chemistry and Technologies, Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy;3. Department of Biology and Biotechnology “Lazzaro Spallanzani”, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy |
| Abstract: | Diphenylene iodonium (DPI) is known for its inhibitory activities against many flavin- and heme-dependent enzymes, and is often used as an NADPH oxidase inhibitor. We probed the efficacy of DPI on two well-known drug targets, the human monoamine oxidases MAO A and B. UV-visible spectrophotometry and steady-state kinetics experiments demonstrate that DPI acts as a competitive and reversible MAO inhibitor with Ki values of 1.7 and 0.3 μM for MAO A and MAO B, respectively. Elucidation of the crystal structure of human MAO B bound to the inhibitor revealed that DPI binds deeply in the active-site cavity to establish multiple hydrophobic interactions with the surrounding side chains and the flavin. These data prove that DPI is a genuine MAO inhibitor and that the inhibition mechanism does not involve a reaction with the reduced flavin. This binding and inhibitory activity against the MAOs, two major reactive oxygen species (ROS)-producing enzymes, will have to be carefully considered when interpreting experiments that rely on DPI for target validation and chemical biology studies on ROS functions. |
