Bioluminescent Assay for MAO Enzyme Inhibition

The two-step bioluminescent assay (MAO-Glo™ Assay Systems; Promega, Madison, WI, United States) was performed in Nunc white, 96-well, flat-bottom assay plates (Life Technologies Europe B.V., Zug, Switzerland) as described previously (Van Der Toorn et al., 2019 (link)). Fluostar Omega 96 Microplate reader (BMG LABTECH GmbH, Ortenberg, Germany) was used to measure the luminescent signal and to determine the IC₅₀ (half maximal inhibitory concentration). Z’ scores were between 0.75 and 0.86 for both MAO A and B assays. The constant (Km) of MAO A was 17.1 and 2.6 µM for MAO B. The substrate concentrations (S) were 20 µM for MAO A assay and 3 µM for MAO B. The Ki values referred in the discussion were calculated accordingly to the following formula: $Ki=I{C}_{50}/\left(1+\frac{Km}{S}\right)$ .