CHEMBL5736836

Biochemical Assay: The purpose of GSK3β assay is to evaluate the inhibition (% inhibition, Kiapp and Ki values) of small molecule inhibitors by using a fluorescence-based microfluidic mobility shift assay. GSK3β catalyzes the production of ADP from ATP that accompanies the phosphoryl transfer to the substrate peptide FL-Peptide-15 (5-FAM-KRREILSRRPpSYR-COOH, CPC Scientific, Sunnyvale, Calif.) (SEQ ID NO:2). The mobility shift assay electrophoretically separates the fluorescently labeled peptides (substrate and phosphorylated product) following the kinase reaction. Both substrate and product are measured and the ratio of these values is used to generate % conversion of substrate to product by the LabChip EZ Reader. Active GSK3β (H350L) was purchased from Upstate/Millipore. Typical reaction solutions (50 μL final reaction volume) contained 2% DMSO (±inhibitor), 4 mM MgCl2, 1 mM DTT, 40 μM ATP (ATP Km=9.43 μM), 0.005% Tween-20, 2 μM FL-Peptide-15, and 0.6 nM GSK3β in 25 mM HEPES buffer at pH 7.5. The assay was initiated with the addition of ATP, following 15 minutes pre-incubation of enzyme and inhibitor at room temperature in the reaction mixture. The reaction was stopped after 30 minutes at room temperature by the addition of 50 μL of 80 mM EDTA. The Ki value was determined from the fit of the data to the Morrison tight-binding competitive inhibition equation with the enzyme concentration as a variable.