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Assay Method Information

Assay Name:  Factor XIa Assay
Description:  The effectiveness of a compound of the present invention as an inhibitor of Coagulation Factor XIa can be determined using a relevant purified serine protease, and an appropriate synthetic substrate. The rate of hydrolysis of the chromogenic or fluorogenic substrate by the relevant serine protease was measured both in the absence and presence of compounds of the present invention. Assays were conducted at rt or at 37 C. Hydrolysis of the substrate resulted in release of amino trifluoromethylcoumarin (AFC), which was monitored spectrofluorometrically by measuring the increase in emission at 510 nm with excitation at 405 nm. A decrease in the rate of fluorescence change in the presence of inhibitor is indicative of enzyme inhibition. Such methods are known to one skilled in the art. The results of this assay are expressed as the inhibitory constant, Ki.Factor XIa determinations were made in 50 mM HEPES buffer at pH 7.4 containing 150 mM NaCl, 5 mM CaCl2, and 0.1% PEG 8000 (polyethylene glycol; JT Baker or Fisher Scientific). Determinations were made using purified human Factor XIa at a final concentration of 40 pM (Sekisui Diagnostics) and he synthetic substrate, Z-Gly-Pro-Arg-AFC, TFA salt (Sigma #C0980) at a concentration of 100 μM.Activity assays were performed by diluting a stock solution of substrate at least tenfold to a final concentration ≤0.1 Km into a solution containing enzyme or enzyme equilibrated with inhibitor. Times required to achieve equilibration between enzyme and inhibitor were determined in control experiments. Initial velocities of product formation in the absence (Vo) or presence of inhibitor (Vi) were measured. Assuming competitive inhibition, and that unity is negligible compared Km/[S], [I]/e, and [I]/e (where [S], [I], and e respectively represent the total concentrations, of substrate, inhibitor and enzyme), the equilibrium constant (Ki) for dissociation of the inhibitor from the enzyme can be obtained from the dependence of Vo/Vi on [I] shown in the following equation.
Affinity data for this assay
 

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Last update November 1, 2007
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