Kinetics of TAFI and protein C activation by the thrombin-Solulin complex in HEPES-buffered saline. TAFI activation (●) was fit by nonlinear regression to the Michaelis-Menten model of enzyme kinetics, yielding a K_m of 0.71μM and a k_cat of 1.09/s, implying a catalytic efficiency of 1.53/μM/s. The kinetic parameters K_m and k_cat cannot be determined for protein C activation by the thrombin-Solulin complex (○); however, the slope provides a reasonable estimate of the catalytic efficiency (k_cat/K_m = 0.02/μM/s).