| Assay Method Information | |
| | Enzyme Activity Assay |
| Description: | Btk enzyme activity is measured using the IMAP (immobilized metal ion affinity-based fluorescence polarization) assay as outlined below.Btk enzyme (His-Btk (Millipore catalog #14-552), is diluted to 0.4 U/mL in KR buffer (10 mM Tris-HCl, 10 mM MgCl2, 0.01% Tween-20, 0.05% NaN3, 1 mM DTT, 2 mM MnCl2, pH 7.2).Serial dilution log 10 from 2 mM to 63.2 nM of test compounds are made in 100% DMSO. The dilutions in DMSO are then diluted 50-fold in KR-buffer. Final compound concentration range in the assay from 10 μM to 0.316 nM.5 μL/well of test compound in KR buffer (final DMSO concentration in the assay is 1%) is mixed with 5 μl/well of 0.4 U/mL Btk enzyme (final concentration in the assay is 0.1 U/mL). Test compounds and Btk enzyme are pre-incubated 60 minutes at room temperature, before adding 5 μL/well of 200 nM Fluorescin labeled substrate peptide (Blk/Lyntide substrate, e.g. #R7188/#R7233, Molecular Devices) in KR-buffer. Final peptide substrate concentration in assay is 50 nM. The kinase assay is started by adding 5 μL/well is of 20 μM ATP in KR-buffer (final ATP concentration is 5 μM ATP, Km ATP in Btk IMAP assay). Following incubation for 2 h at room temperature the enzyme reaction is stopped by adding 40 μL/well IMAP Progressive Binding Solution (according to suppliers (Molecular Devices) protocol using 75% 1× buffer A and 25% 1× buffer B with 1:600 Progressive Binding Solution). After 60 min incubation at room temperature in the dark the FP signal is read. Fluorescence at 535 nm is measured using parallel and perpendicular filters to determine differences in rotation due to binding of the phosphorylated substrate peptide to the beads. Values are calculated as percentage of the difference in readout (ΔmPi) of the controls with and without ATP. |
| Affinity data for this assay | |
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