Polyphosphate accelerates factor V activation by factor XIa

• DOI: 10.1160/th14-06-0515
• Publication Date: 2014-10-23T13:13:47Z
• Authors: Sharon Choi; Stephanie Smith; James Morrissey
• Keywords: Prothrombinase; Factor V; Polyphosphate

Factor Va enhances the rate of prothrombin activation by factor Xa four to five orders magnitude. Production initiating levels from its precursor, V, is a critical event early in haemostasis, as V exhibits negligible cofactor activity. While thrombin most potent physiological back-activator first prothrombinase complexes require source prior generation. A recent study Whelihan et al. (J Thromb Haemost 2010; 8:1532-1539) identified XIa candidate for initial thrombin-independent although this reaction was slow and required relatively high concentrations factors XIa. Activated platelets secrete polyphosphate, which we previously showed be potently procoagulant. We now report that polyphosphate greatly accelerates XIa, supported polymers size secreted activated human platelets. This finding provides additional evidence XIa-mediated generation may contribute initiation haemostasis.