*2.5. Monoamine Oxidase (MAO) Activity Assay*

MAO-B activity was measured using the MAO assay kit (Cell Biolabs, San Diego, CA, USA) according to the manufacturer's instructions. Human MAO-B (50 μg/mL; Sigma-Aldrich) was incubated with 1 mM WY dipeptide or 1 mM tryptophan for 30 min. The substrates for MAO-B were added and the amount of hydrogen peroxide in the reaction was measured.
