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Assay Method Information |
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| | Inhibition In Vitro Assay |
| Description: | PDE4A, PDE4B, PDE4C, PDE4D, and PDE5 human recombinant proteins are expressed and purified from Saccharomyes cerevisiae that lack endogenous PDEs. The phosphodiesterase enzymes are diluted on ice with enzyme dilution buffer (25 mM Tris, pH 7.5, 0.1 mM DTT, 5.0 mM MgCl2, 100 mM NaCl, 5 μM ZnSO4, 100 μg/mL BSA) to give approximately 20%-40% hydrolysis of cyclic nucleotide monophosphate (cNMP) in the absence of inhibitor. The stock solution of test compounds are diluted on the Beckman BioMek 1000 workstation to span a concentration range of 4.5 log units in 0.5 log increments. The DMSO concentration in the final test system is 2.5% for all PDE enzymes. The final test compound concentration tested ranged from 0.03 nM to 1 μM. The assay is performed in a 96-well microtiter plate format on a Beckman BioMek 1000 robotic station. Each row of the plate represents a 10-point dose response curve containing blank (no enzyme), non-inhibited control, and inhibitor dilutions spanning 4.5 log units in concentration in 0.5 log increments. Assay stock solutions are loaded into the Biomek reservoirs (water, inhibitor diluent [2.5% or 10% DMSO], 5× PDE assay buffer, substrate, inhibitor solutions, enzyme solutions, snake venom nucleotidase, and charcoal suspension). The reaction is initiated with enzyme, and incubated for 15 minutes at 30° C. An excess of Crotalus atrox snake venom nucleotidase (5 μL/well) is then added and the mixture is incubated for an additional 3 minutes. The reaction is terminated by the addition of 200 μL of activated charcoal suspension, after which the plate is centrifuged for 5 minutes at 750×g. A transfer program is run in which 200 μL of supernatant is removed and placed into a new plate. The amount of radioactivity released as phosphate is determined in a Wallac MicroBeta Plate counter. |
| Affinity data for this assay | |
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