Comparison of the factor X–activating activity of plasma factor IXa and factor IXaR94S in the presence of polylysine. Human factor X (600 nmol/L) was activated by 50 nmol/L plasma factor IXa (○) or factor IXaR94S (•) in the presence of polylysine (60 nmol/L) in 0.1 mol/L triethanolamine, 0.1 mol/L NaCl, 0.1% PEG 6000, pH 9.0 buffer at 37°C. At discrete time intervals, aliquots of the reactions were assayed for factor Xa concentration using CHG-GR-pNA. The results are expressed as concentration of factor Xa formed as a function of time. The solid lines represent the linear regression fit to the data. The initial rate of factor X activation by plasma factor IXa and factor IXaR94S was 2.54 ± 0.07 nmol/L/min⁻¹ and 0.19 ± 0.01 nmol/L/min⁻¹, respectively.