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Assay Method Information

Assay Name:  A2 PI3Kdelta Scintillation Proximity Assay
Description:  Lipid kinase substrate, phosphoinositol-4,5-bisphosphate (PIP2), are purchased from Echelon Biosciences (Salt Lake City, Utah). PI3K isoforms α, β, δ and γ are purchased from Millipore (Bedford, Mass.). ATP, MgCl2, DTT, EDTA, MOPS and CHAPS are purchased from Sigma-Aldrich (St. Louis, Mo.). The kinase reaction are conducted in clear-bottom 96-well plate from Thermo Fisher Scientific in a final volume of 24 μL. Inhibitors are first diluted serially in DMSO and added to the plate wells before the addition of other reaction components. The final concentration of DMSO in the assay is 0.5%. The PI3K assays are carried out at room temperature in 20 mM MOPS, pH 6.7, 10 mM MgCl2, 5 mM DTT and CHAPS 0.03%. The reaction mixture is prepared containing 50 μM PIP2, kinase and varying concentration of inhibitors. Reactions are initiated by the addition of ATP containing 2.2 μCi [γ-33P]ATP to a final concentration of 1000 μM. The final concentration of PI3K isoforms α, β, δ and γ in the assay were 1.3, 9.4, 2.9 and 10.8 nM, respectively. Reactions are incubated for 180 minutes and terminated by the addition of 100 μL of 1 M potassium phosphate pH 8.0, 30 mM EDTA quench buffer. A 100 μL aliquot of the reaction solution are then transferred to 96-well Millipore MultiScreen IP 0.45 μm PVDF filter plate (The filter plate is prewetted with 200 μL 100% ethanol, distilled water, and 1 M potassium phosphate pH 8.0, respectively). The filter plate is aspirated on a Millipore Manifold under vacuum and washed with 18200 μL wash buffer containing 1 M potassium phosphate pH 8.0 and 1 mM ATP. After drying by aspiration and blotting, the plate is air dried in an incubator at 37 C. overnight. Packard TopCount adapter (Millipore) is then attached to the plate followed with addition of 120 μL Microscint 20 scintillation cocktail (Perkin Elmer) in each well. After the plate sealing, the radioactivity of the product is determined by scintillation counting on Topcount (Perkin-Elmer). IC50 determination is performed by fitting the curve of percent control activity versus the log of the inhibitor concentration using the GraphPad Prism 3.0 software.
Affinity data for this assay
 

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Last update November 1, 2007
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