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Updated: Jul 21, 2026

A Novel In vitro Model for Studying the Interactions Between Human Whole Blood and Endothelium
Published on: November 21, 2014
Factor XI activation in a revised model of blood coagulation
1Department of Medicine, Jewish Hospital, Washington University Medical Center, St. Louis, MO 63110.
Abstract:
Coagulation factor XI is activated in vitro by factor XIIa in the presence of high molecular weight kininogen (HMWK) and a negatively charged surface. Factor XII deficiency is not associated with bleeding, which suggests that another mechanism for factor XI activation exists in vivo. A revised model of coagulation is proposed in which factor XI is activated by thrombin. In the absence of cofactors, thrombin is more effective (kcat/Km = 1.6 x 10(5)) than factor XIIa (1.7 x 10(4)) in activating factor XI. Dextran sulfate enhances activation of factor XI by thrombin 2000-fold; part of this effect is due to autoactivation of factor XI by activated factor XI.
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