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Assay Method Information

Assay Name:  JAK Enzyme Assays
Description:  The activity of the isolated recombinant JAK1 and JAK2 kinase domain was measured by monitoring phosphorylation of a peptide derived from JAK3 (Val-Ala-Leu-Val-Asp-Gly-Tyr-Phe-Arg-Leu-Thr-Thr, fluorescently labeled on the N-terminus with 5-carboxyfluorescein) using the Caliper LabChip® technology (Caliper Life Sciences, Hopkinton, Mass.). To determine inhibition constants (Ki), compounds were diluted serially in DMSO and added to 50 μL kinase reactions containing purified enzyme (1.5 nM JAK1, or 0.2 nM JAK2), 100 mM HEPES buffer (pH 7.2), 0.015% Brij-35, 1.5 μM peptide substrate, ATP (25 μM), 10 mM MgCl2, 4 mM DTT at a final DMSO concentration of 2%. Reactions were incubated at 22° C. in 384-well polypropylene microtiter plates for 30 minutes and then stopped by addition of 25 μL of an EDTA containing solution (100 mM HEPES buffer (pH 7.2), 0.015% Brij-35, 150 mM EDTA), resulting in a final EDTA concentration of 50 mM. After termination of the kinase reaction, the proportion of phosphorylated product was determined as a fraction of total peptide substrate using the Caliper LabChip® 3000 according to the manufacturer's specifications. Ki values were then determined using the Morrison tight binding model (Morrison, J. F., Biochim. Biophys. Acta. 185:269-296 (1969); William, J. W. and Morrison, J. F., Meth. Enzymol., 63:437-467 (1979)) modified for ATP-competitive inhibition [Ki=Ki,app/(1+[ATP]/Km,app)].
Affinity data for this assay
 

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Last update November 1, 2007
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