von Willebrand Factor

a.k.a. vWF is a multimeric protein produced in the endothelium and subendothelial tissues, and also in the alpha granules within platelets. vWF is bound to Factor VIII while inactive and released by the influence of thrombin and binds to subendothelial collagen during vessel trauma and damage. vWF then binds to platelets via the GPIb receptor. Additional platelets bind via vWF and the process repeats. The breakdown of vWF multimers is by ADAMTS13, a metalloproteinase.