Comparison of the amidolytic activity of plasma factor IXa and factor IXaR94S. Varying concentrations of plasma factor IXa (○) or factor IXaR94S (•) were incubated with 2.5 mmol/L CHG-GR-pNA in TBS containing 0.1% BSA, and the increase in absorbance at 405 nm with time was measured. The initial velocity of p-nitroaniline formation is expressed as a function of enzyme concentration. The solid lines represent the linear regression fit to the data. The observed rate of hydrolysis of CHG-GR-pNA by plasma factor IXa and factor IXaR94S was 1.51 ± 0.06 min⁻¹ and 1.68 ± 0.02 min⁻¹, respectively.