A cofactor for factor XI activation

Abstract

During formation of a blood clot, the key enzyme thrombin is formed through the coordinated activities of a group of plasma proteases (factors VIIa, IXa, Xa, and XIa). Central to this process are protein "cofactors" (tissue factor, and factors Va and VIIIa) that facilitate the activation and/or activity of the plasma proteases on membranes of platelets and tissues. In this issue of Blood, Choi and colleagues present intriguing results showing that a nonprotein, inorganic polyphosphate (PolyP), can enhance thrombin generation by serving as a cofactor for formation of factor XIa.