LED fluorescence spectroscopy for direct determination of monoamine oxidase B inactivation

In this work, we report an alternative assay for the determination of the inhibitory effect on monoamine oxidase B (MAO-B) activity of probe compounds. Enzyme MAO-B exhibits fluorescence emissions when it is excited at 412 nm. Using an inexpensive blue LED-like excitation source, we measured the quenching of fluorescence intensity of MAO-B enzyme during the reaction with inhibitors. The applicability of the procedure is demonstrated by assays with l-deprenyl and berberine as inhibitors through the use of fluorescence studies. The IC50 values of l-deprenyl and berberine were 0.04 and 90 μM, respectively. The KI values were 0.020 and 47 μM for l-deprenyl and berberine, respectively. These IC50 and KI values were similar to the values obtained with a standard method. These results demonstrate the feasibility of this method as an alternative to follow the inhibitory effect on MAO-B.