Radioenzymatic Assay: The enzyme activity was assessed with a radioenzymatic assay using the substrate 14C-phenylethylamine (PEA) specific for MAO-B.The mitochondrial pellet (500 μg protein) was resuspended in 0.1 M phosphate buffer (pH 7.4). 200 μl of the suspension were added to a 50 μl solution of the test compound or buffer, and incubated for 30 min at 37° C. (preincubation) then the substrate (50 μl) was added. The incubation was carried out for 10 minutes at 37° C. (14C-PEA, 0.5 μM).The reaction was stopped by adding 0.2 ml of perchloric acid. After centrifugation, the deaminated metabolites were extracted with 3 ml of toluene and the radioactive organic phase containing the neutral and/or acidic metabolites formed as a result of MAO-B activity was measured by liquid scintillation spectrometry at 90% efficiency.
Inhibition Assay: Test compound is dissolved in DMSO 500× the highest final concentration desired in the IC50 assay. 30 ml of deionized water is pre-warmed to 37° C. and all kit components are placed on ice. For each well of column 1, 149.4 μL of NADPH-Cofactor Mix, (187.5 μl of Cofactors, 150 μl of G6PDH, 100 μl of Control Protein and 14.56 ml of 37° C. water) are added. In each well from Column 2 to 12, 100 μl of Cofactor/DMSO mix (40 μL DMSO in 9.96 ml of NADPH-Cofactor Mix) are added. To each well of column 1, 0.6 μl of test compound or positive control are added. 50 μl from each well of column 1 are serially diluted to column 8. The extra 50 μl from column 8 are discarded. The plate is covered and pre-incubated at 37° C. for 10 minutes. Preparation of enzyme/substrate mix: 7.92 ml of pre-warmed deionized water, 75 μl of enzyme, 3 μl of 10 mM AMMC and 2 ml of pre-warmed buffer are mixed. After the pre-incubation time (10'), 100 μl of enzyme/substrate mix to each well from column 1 to 10 are added. The plate is incubated at 37° C. for 30 minutes. After this time, 75 μl of Stop Reagent to each well are added. For blank controls, 100 μl of enzyme/substrate mix are added to columns 11 and 12.