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Assay Method Information

Assay Name:  JAK Enzymatic Assay
Description:  Enzyme inhibition studies were performed using recombinant JAK1 (amino acids 866-1154, Life Technologies, #PV4774, Carlsbad, Calif.), JAK2 (amino acids 831-1132), or JAK3 (amino acids 781-1124) under buffer conditions of 50 mM HEPES pH 7.3, 1 mM DTT, 0.01% TweenŽ 20, 50 μg/mL BSA, and 10 mM MgCl2. JAK enzyme was expressed as an N-terminal GST fusion in insect cells and purified by glutathione-affinity and size-exclusion chromatographies. Enzymes were assayed both at their respective ATP Km (JAK1: 55 μM, JAK2: 15 μM, JAK3: 3 μM) and the approximated high end of physiological ATP concentration of 5 mM, in the presence of inhibitor dosed at 30, 3, 0.3, 0.03, 0.003 and 0 μM final test concentrations. For JAK1, 6 nM of enzyme (for Km ATP assay) or 4 nM enzyme (for high ATP assay) was incubated with 1.5 μM peptide substrate (FITC-C6-KKHTDDGYMPMSPGVA-NH2 (SEQ ID NO:1), Intonation, Boston, Mass.). For JAK2, 0.8 nM of enzyme (for Km ATP assay) or 0.3 nM enzyme (for high ATP assay) was incubated with 1.5 μM peptide substrate (5FAM-GEEPLYWSFPAKKK-NH2 (SEQ ID NO:2), Intonation, Boston, Mass.). For JAK3, 0.2 nM of enzyme (for Km ATP assay) or 0.1 nM enzyme (for high ATP assay) was incubated with 1.5 μM peptide substrate (5FAM-GEEPLYWSFPAKKK-NH2 (SEQ ID NO:2), Intonation, Boston, Mass.). Phosphorylated and unphosphorylated peptides were separated and quantified by a Caliper LC3000 system (Caliper Life Sciences, MA) for calculating percent inhibition. The results of this assay are shown in Table 16 and indicate that the compounds of Formula (I), (Ia), (Ib) and Table 1 exhibit preferential inhibition of JAK1 over JAK2 (in many cases demonstrating over 100 times selectivity for inhibition of JAK1 vs. JAK2).
Affinity data for this assay
 

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Last update November 1, 2007
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