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| | Fluorescence-Based (Inhibitor)-Screening Assay |
| Description: | In order to monitor MAO enzymatic activities and/or their inhibition rate by inhibitor(s) of interest, a fluorescence-based (inhibitor)-screening assay was set up. 3-(2-Aminophenyl)-3-oxopropanamine (kynuramine dihydrobromide, Sigma Aldrich), a non fluorescent compound was chosen as a substrate. Kynuramine is a non-specific substrate for both MAO-A and MAO-B activities. While undergoing oxidative deamination by MAO activities, kynuramine is converted into 4-hydroxyquinoline (4-HQ), a resulting fluorescent product.The monoamine oxidase activity was estimated by measuring the conversion of kynuramine into 4-hydroxyquinoline. Assays were conducted in 96-well black plates with clear bottom (Corning) in a final volume of 100 uL. The assay buffer was 100 mM HEPES, pH 7.5. Each experiment was performed in duplicate within the same experiment.Briefly, a fixed amount of MAO (0.25 ug for MAO-A and 0.5 ug for MAO-B) was incubated on ice for 15 minutes in the reaction buffer, in the absence and/or in the presence of at least eight 3-fold serial dilutions each. Clorgyline and Deprenyl (Sigma Aldrich) was used as a control for specific inhibition of MAO-A and MAO-B respectively. After leaving the enzyme(s) interacting with the inhibitor, KM of kynuramine was added to each reaction for MAO-B and MAO-A assay respectively, and the reaction was left for 1 hour at 37° C. in the dark. The oxidative deamination of the substrate was stopped by adding 50 uL of NaOH 2N. The conversion of kynuramine to 4-hydroxyquinoline, was monitored by fluorescence (excitation at 320 nm, emission at 360 nm) using a microplate reader (Infinite 200, Tecan). Arbitrary units were used to measure levels of fluorescence produced in the absence and/or in the presence of inhibitor. The maximum of oxidative deamination activity was obtained by measuring the amount of 4-hydroxyquinoline formed from kynuramine deamination in the absence of inhibitor and corrected for background fluorescence in the absence of MAO enzymes. The IC50 values of each inhibitor were calculated with GraphPad Prism Software. |
| Affinity data for this assay | |
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