| Assay Method Information | |
| | In Vitro Testing of Human Factor Xa Assay |
| Description: | Measurement of active human Factor Xa using a specific chromogenic substrate which is labeled with a p-nitro-anilino group (pNA). The cleavage in between the binding of the peptide substrate and the pNA-group is followed by a color change, which can be detected at 405 nm. The amount of cleaved substrate is directly proportional to the amount of active Xa.0.8 mg (100 U) human Factor Xa (Enzyme Research Laboratories; HFXa1011) were solved in 0.444 ml H2O (Millipore), which accords to a stock solution of 19.28 μM or 225 U/ml. Further dilutions were made in the assay buffer (Tris 100 mM, NaCL 150 mM, adjusted to a pH of 7.8 with HCL, containing 0.1% BSA and 0.05% Tween20). 25 mg (1 vial) of the chromogenic substrate S2765 (Chromogenix; S2765) was solved in 3.5 ml H2O (Millipore) to achieve a stock solution of 10 mM.Compounds were solved and diluted in DMSO where the final dilution in the assay is 1:10 resulting in a final concentration of 1% DMSO.compounds solved in H2O were diluted in H2O the prefinal dilution step was 1:10 in the assay buffer containing 11% DMSO resulting in 10% DMSO final dilution in the assay is 1:10 resulting in a final concentration of 1% DMSO Compounds were tested at final concentrations of 10 μM to 0.003 nM or lower. 5 μl human factor Xa (final concentration 0.86 nM), 2 μl compound dilution or assay buffer (containing 10% DMSO) and 8 μl assay buffer were pipetted in triplicates into a 384-well plate and incubated in the Thermomix at 24° C. for 10 minutes. After addition of 5 μl chromogenic substrate (final concentration 0.5 mM) the enzyme-substrate reaction started and the kinetic measurement with the SpectraMax Monochromator was started within 1-2 minutes. Parameter of measurement: (Spectra ax, Monochromator) Absorbance; 1.LM 405 nM Kinetic: 16 min each 2nd minute (9 times) Negative Control (NC) 5 μl human factor Xa+10 μl assay buffer+5 μl Substrate Positive Control (PC): 5 μl human factor Xa+2 μl Nafamostat (commercially available, final concentration: 1 μM)+8 μl assay buffer+5 μl Substraten Blank (optional): 15 μl assay buffer+5 μl Substrate Calculation of IC50, KI and the % effect at the highest concentration (Ratio). |
| Affinity data for this assay | |
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