Assay Method Information

Assay Name:  FRET-displacement assay
Description:  FRET assays to determine Ki for the compounds of Table I were carried out as described previously (Lee et al. Analytical Biochemistry 434 (2013) 259-268). In order to prevent leaching of fluorescence impurities from the plastic tube and non-specific binding to sEH inhibitors, the inhibitor stock solution (10 mM, DMSO) was stored in glass vials. In addition, sEH was diluted to desired concentration (20 nM) with sodium phosphate buffer (PB) (100 mM sodium phosphate, pH 7.4, 0.01% gelatin) to avoid loss of protein from non-specific binding to the cuvette surface. All buffer used in this assay was filtered by sterilized filtration unit (Millipore Durapore PVDF Membrane, pore size: 0.22 um).Measurement in 96-Well PlatesAll the measurement for FRET-based displacement assay in 96-well plate format were done in TECAN Infinite M1000 Pro 96 well fluorescence plate reader.Pre-Treatment of 96-Well PlateIn order to prevent non-specific binding of sEH or inhibitor on the 96-well plate, the 96 well plates were pre-incubated with PB with 0.1% gelatin overnight at rt. The gelatin coats the plate and prevents non-specific binding of sEH and sEH inhibitors to the plate. The buffer was discarded and the plate was dried before use.Assay ProcedureThe sEH stock was diluted to the desired concentration (20 nM) by PB (100 mM sodium phosphate, 0.1% gelatin, pH 7.4). ACPU (one equivalent to sEH, 10 mM, Ethanol) was added to the sEH solution and was incubated for 2 h at rt. The sEH-ACPU mixture (20 nM, 100 mM sodium phosphate, 0.1% gelatin, pH 7.4, 150 uL) was added to each well.The baseline fluorescence (F0) (λexcitation at 280 nm, λemission at 450 nm) of the samples was measured after the z-position and gain were optimized automatically by the fluorometers. The z and gain value was noted and will be used for the later fluorescent measurement. Because DMSO has been known to quench fluorescence. 1% DMSO in PB was served as a control (FDMSO). The desired concentration of inhibitors which is the concentration that 100% of sEH was bound to inhibitor, was added at the first well and was further diluted by 2-fold across the rest of the wells. Based on our study, 12 datum points which correspond to 12 different concentrations of the inhibitor, provide significant data to calculate the accurate Ki for the inhibitors. The samples were incubated at 30 C. for 1.5 h. Then, the fluorescence (λexcitation at 280 nm, λemission at 450 nm) of the samples was measured using the z-position and gain values that previously obtained.
Affinity data for this assay
 

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