Human factor XIa (fXIa and active-site labeled
fluorescein-EGR-fXIa (fEGR-fXIa)) was purchased from
Haematologic Technologies (Essex Junction, VT). Recombinant fXIa containing
only the catalytic domain (fXIa-CD) was a gift from Dr. Alireza Rezaie
(St. Louis University, MO). Chromogenic substrate S-2366 (l-pyroglutamyl-l-prolyl-l-arginine-p-nitroaniline) was purchased from Diapharma (West Chester, OH). Stock
solutions of fXIa were prepared in 0.05 M Tris-HCl buffer, pH 7.4,
containing 0.15 M NaCl and 0.1% PEG8000. The buffer used in inhibition
studies was 0.05 M Tris-HCl buffer, pH 7.4, containing 0.15 M NaCl,
0.1% PEG8000, and 0.02% Tween80, while that used for all other studies
was devoid of 0.02% Tween80. All of the other chemicals were of biochemical
grade and purchased either from Sigma-Aldrich (St. Louis, MO) or from
Fisher Scientific (Pittsburgh, PA). The sulfated small molecules used
in this study were prepared earlier, as described in a series of articles,22 (link),24 (link)−33 (link) and were more than 95% pure. In these studies, purity was assessed
by a combination of techniques including HPLC/UPLC, HR-MS, and/or
elemental analysis.