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Assay Method Information

Assay Name:  TR-FRET Assay
Description:  The β-secretase enzyme used in the TR-FRET is prepared as follows: The cDNA for the soluble part of the human β-Secretase (AA 1-AA 460) was cloned using the ASP2-Fc 10-1-IRES-GFP-neoK mammalian expression vector. The gene was fused to the Fc domain of IgG1 (affinity tag) and stably cloned into HEK 293 cells. Purified sBACE-Fc was stored in −80 C. in Tris buffer, pH 9.2 and had a purity of 40%.The enzyme (truncated form) was diluted to 6 μg/mL (stock 1.3 mg/mL) and the substrate (Europium)CEVNLDAEFK(Qsy7) to 200 nM (stock 120 μM) in reaction buffer (NaAcetate, chaps, triton x-100, EDTA pH4.5). The robotic systems Biomek FX and Velocity 11 were used for all liquid handling and the enzyme and substrate solutions were kept on ice until they were placed in the robotic system. Enzyme (9 μl) was added to the plate then 1 μl of compound in dimethylsulphoxide was added, mixed and pre-incubated for 10 minutes. Substrate (10 μl) was then added, mixed and the reaction proceeded for 15 minutes at r.t. The reaction was stopped with the addition of Stop solution (7 μl, NaAcetate, pH 9). The fluorescence of the product was measured on a Victor II plate reader with an excitation wavelength of 340 nm and an emission wavelength of 615 nm. The assay was performed in a Costar 384 well round bottom, low volume, non-binding surface plate (Corning #3676). The final concentration of the enzyme was 2.7 g/ml; the final concentration of substrate was 100 nM (Km of 250 nM). The dimethylsulphoxide control, instead of test compound, defined the 100% activity level and 0% activity was defined by wells lacking enzyme (replaced with reaction buffer). A control inhibitor was also used in dose response assays and had an IC50 of 150 nM.
Affinity data for this assay
 

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Last update November 1, 2007
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