Effect of fibrinogen γ′ peptides on protein C activation by the thrombin/sTM complex. Purified protein C (500 nM) was activated with thrombin (5 nM) and sTM (10 nM) in the presence of 0 to 500 µM WT-S12 (A) or SCR-S12 (B) peptide. Subsamples were taken from the activation mix after 30 and 60 minutes and were assayed for APC activity. Rates of protein C activation were plotted as a function of peptide concentration and fitted to the equation of a rectangular hyperbola (C).