Plasma thrombin clotting assay. (A) Time to clot formation after addition of various concentrations of α-thrombin (listed at bottom) to pooled normal plasma collected into 0.32% sodium citrate in the absence of recalcification. The column at the extreme left shows results for plasma in the absence of recalcification or added thrombin, whereas the second column from the left shows that plasma does not clot after recalcification in the absence of added thrombin. (B) Time to clot formation after addition of various concentrations of Mz-IIa, β-IIa, or γ-IIa to pooled normal plasma collected into 0.32% sodium citrate in the absence of recalcification. Forms and final concentrations indicated at the bottom of the panel. (C-F) Time to clot formation after addition of (C) 1.25nM α-IIa, (D) 2.5nM rMz-IIa, (E) 5nM β-IIa, or (F) 10nM γ-IIa to pooled normal plasma collected into 0.32% sodium citrate, with (+Ca²⁺) or without (−Ca²⁺) recalcification. Recalcified reactions were run in the presence of vehicle (V), an IgG that blocks FIX activation by FXIa (O1A6), an IgG that blocks FXI activation by FXIIa (14E11), or a FXIIa inhibitor (CTI). For panel F, reactions are also run in the presence of ovomucoid trypsin inhibitor (OTI). For all panels, each symbol indicates a single clotting time, and bars indicate the mean clotting time for each group.