Equilibrium and kinetics of EP compound binding to thrombin. (A) Comparison of equilibrium binding titrations of 0.12 and 1.2nM thrombin with EP217609 monitored from the decrease in the initial rate of S2366 substrate hydrolysis by thrombin. Solid lines indicate fits by the equation for tight binding competitive inhibition. (B) Plot of kobs versus the effective [EP compound], obtained by dividing by the factor, 1 + [S]o/KM, for the binding of EP42675 (○) and EP217609 (●) to thrombin. kobs was measured from exponential progress curves of the time-dependent inhibition of thrombin hydrolysis of the low KM substrate, tosyl-GPR-AMC. The slope of this plot provided kon and the intercept provided koff.