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Assay Method Information

Assay Name:  Factor XIa Assay
Description:  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 the synthetic substrate, Z-Gly-Pro-Arg-AFC, TFA salt (Sigma #C0980) at a concentration of 10004.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.V o /V i=1+[I]/Ki.
Affinity data for this assay
 

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Last update November 1, 2007
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