| Assay Method Information | |
| | Enzyme Assays |
| Description: | All 3′, 5′ cyclic nucleotide phosphodiesterase (PDE) enzyme activities are measured with a radiometric enzyme assay based on SPA detection system (scintillation proximity assay). Compounds to be tested are diluted in pure dimethyl sulfoxide (DMSO) using ten point concentration response curves. Maximal compound concentration in the reaction mixture is either 10 or 100 μM. Compounds at the appropriate concentration are pre-incubated with either of the PDE enzymes for 30 minutes before the reaction is started by the addition of substrate. Reactions are allowed to proceed for 60 minutes at room temperature. Next, reactions are stopped by addition of SPA beads. Samples are read 12 hours later in a MICROBETA TRILUX Counter. IC50 refers to the concentration of the compound that produces 50% of the maximal inhibitory response possible for that compound. IC50 values are calculated by plotting the normalized data vs. log [compound] and fitting the data using a four parameter logistic equation. PDE1B, PDE1A, and PDE1C: The assay buffer is prepared to give a final concentration in the assay of 50 mM Tris-HCl, 50 mM MgC2, 4 mM CaCl2, 0.1% Bovine serum albumin and 6 U/ml Calmodulin in water, at pH 7.5. The final enzyme concentration is 0.25, 0.074 and 0.0012 nM, for PDE1A, PDE1B and PDE1C respectively. PDE3A,and PDE4D: he assay buffer is prepared to give a final concentration in the assay of 50 mM Tris-HCl, 8.3 mM MgCl2, 1.7 mM ethylenediarninetetraacetic acid (EDTA) and 0.1% Bovine serum albumin at pH 7.5. Final enzyme concentrations are 0.008 and 0.021 nM for PDE3A and PDE4D, respectively. PDE6A/6B: The catalytic active form of human PDE6 is a dimer composed of a α (human PDE6A) and β subunit (human PDE6B). The dimer of human PDE6A/6B is produced by the expression and purification strategy, using two purification steps, i.e., NiNTA and anti-FLAG Sepharose chromatography. The assay buffer is prepared to give a final concentration in the assay of 50 mM Tris-HCl, 8.3 mM MgC2, 1.7 mM EDTA and 0.1% Bovine serum albumin at pH 7.5. The final enzyme concentration is 5 nM. The reactions are started by addition of the substrate, [3H]cGMP, to give a final concentration of 80 nM. |
| Affinity data for this assay | |
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