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Assay Method Information

Assay Name:  ERalpha (Wild Type), ERalpha (Y537ERalpha (Wild Type), ERalph (Y537S Mutant) and ERbeta Competition Binding Assay
Description:  The purpose of the following ER competition binding assays is to determine the affinity of a test compound against ERα (wild type), ERα (Y537S mutant), and ERβ.Run the competition binding assay in a buffer containing 50 mM HEPES, pH 7.5, 1.5 mM EDTA, 150 mM NaCl, 10% glycerol, 1 mg/mL ovalbumin, and 5 mM DTT, using 0.025 μCi per well 3H-estradiol (118 μCi/mmol, 1 mCi/mL), 7.2 ng/well ERα (wild type), or 7.2 ng/well ERα (Y537S mutant) or 7.7 ng/well ERβ receptor. Add the test compound at 10 different concentrations ranging from 10,000 nM to 0.5 nM, and determine nonspecific binding in the presence of 1 μM of 17-β estradiol. Incubate the binding reaction (140 μL) for 4 hours at room temperature, and then add cold dextran-charcoal buffer (70 μL) (containing per 50 mL of assay buffer, 0.75 g of charcoal and 0.25 g of dextran) to each reaction. Mix the plates for 8 minutes on an orbital shaker at 4° C. and then centrifuge at 3000 rpm at 4° C. for 10 minutes. Transfer an aliquot (120 μL) of the mixture to another 96-well, white flat bottom plate (Costar) and add Perkin Elmer Optiphase Supermix scintillation fluid (175 μL) to each well. Seal the plates and shake vigorously on an orbital shaker. After an incubation of 2.5 hours, read the plates in a Wallac Microbeta counter. Calculate the IC50 using a 4-parameter logistic curve fit and calculate % inhibition at 10 μM. Convert the IC50 values for the compound to Ki using Cheng-Prusoff equation. The results of this assay demonstrate Examples 1, 1A, and 1B (and others) bind to recombinant ERα wild type and ERα mutant (Y537S) as shown in Table 7 below and Example 1B was also determined to bind to ERβ with a Ki (nM) ERβ competition of 0.11±0.07, n=3.
Affinity data for this assay
 

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Last update November 1, 2007
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