|Protein Kinase Assays
||The in vitro kinase assays are performed in 96-well plates (30 μL) at ambient temperature for 15–45 min using the recombinant glutathione S-transferase-fused kinase domains (4-100 ng, depending on specific activity). [γ33P]ATP is used as phosphate donor and polyGluTyr-(4:1) peptide as acceptor. With the exception of protein kinase C-α, cyclin-dependent kinase 1/cycB and protein kinase A are protamine sulfate (200 μg/mL), histone H1 (100 μg/mL), and the heptapeptide Leu-Arg-Arg-Ala-Ser-Leu-Gly (known as Kemptide Bachem) respectively and are used as peptide substrates. Assays are optimized for each kinase using the following ATP concentrations: 1.0 μM (c-Kit, c-Met, c-Fms, c-Raf-1, and RET), 2.0 μM (EGFR, erbB2, ErbB3, and ErbB4), 5.0 μM (c-abl), 8.0 μM (Flt-1, Flt-3, Flt-4, Flk, KDR, FGFR-1, and Tek), 10.0 μM (PDGFR-β, protein kinase C-α, and cyclin-dependent kinase 1), and 20.0 μM (c-Src and protein kinase A). The reaction is terminated by the addition of 20 μL 125 mM EDTA. Thirty μL (c-abl, c-Src, insulin-like growth factor-1R, RET-Men2A, and RET-Men2B) or 40 μL (all other kinases) of the reaction mixture is transferred onto Immobilon-polyvinylidene difluoride membrane, presoaked with 0.5% H3PO4 and mounted on a vacuum manifold. Vacuum is then applied and each well rinsed with 200 μL 0.5% H3PO4. Membranes are removed and washed four times with 1.0% H3PO4 and once with ethanol. Dried membranes are counted after mounting in a Packard TopCount 96-well frame and with the addition of 10 μL/well of Microscint. IC50 values (±SE) are calculated by linear regression analysis of the percentage inhibition and are averages of at least three determinations.