Thrombomodulin-dependent protein C activation. Samples of thrombin (IIa), meizothrombin(desF1) (aaMZdesF1a), and meizothrombin (aaMZa) were incubated for 30 minutes with protein C in the presence of membrane-associated recombinant human thrombomodulin (▪) or mutant thrombomodulin IdE5 lacking the fifth EGF domain (□). The activated protein C product was quantitated by hydrolysis of chromogenic substrate S-2366. Error bars represent standard error of the mean (SEM).