Physiological activation of protein C on the endothelial cell surface requires the binding of protein C to the endothelial protein C receptor PROCR (EPCR) as well as binding of thrombin to thrombomodulin (TM) (Stavenuiter et al. 2013). PROCR binding to protein C (Fukudome & Esmon 1994) augments by at least 5-fold the effect of thrombin-thrombomodulin on the rate of protein C activation (Stearns-Kurosawa et al. 1996, Taylor et al. 2001).