Inhibition Assay : Inhibitory activity against factor IXa was tested using the substrate SPECTROFLUOR FIXa (american diagnostica inc.; 500 West Avenue, Stamford, Conn. 06902 USA; Pr. No. 299F) and human factor IXa (american diagnostica inc.; Pr. No. 449b). Test substances dissolved in buffer A (50 mM α,α,α-tris (hydroxymethyl)methylamine (Tris), 100 mM NaCl, 5 mM CaCl2, 15% (v/v) ethylene glycol, pH 8.0) were mixed with factor IXa (2.0 μg/ml final concentration). The enzyme reaction was started by addition of SPECTROFLUOR FIXa (100 μM final concentration). After incubation for 60 minutes at room temperature, the reaction was stopped by the addition of 20% (v/v) acetic acid solution, and then measured the fluorescence value (Excitation Wavelength: 355 nm, Emission Wavelength; 460 nm) in a microtiter plate reader (ARVO 1420 Multilabel Counter; PerkinElmer).