Fig. 2.
Time course of the pentasaccharide-catalyzed inhibition of factor Xa or prothrombinase by human plasma antithrombin.
Factor Xa (1 nM) was incubated with 500 nM plasma antithrombin in complex with 5 nM pentasaccharide in the absence (○) or the presence of 50 μM PC/PS minus (●) or plus 5 nM factor Va (■) in TBS buffer containing 1 mg/mL BSA, 0.1% PEG 8000, and 2.5 mM Ca++. At the indicated time points, aliquots of the reaction were removed to 500 μM SpFXa containing 1 mg/mL Polybrene (Sigma), and the remaining enzyme activity was determined by an amidolytic activity assay using Spectrozyme Fxa (American Diagnostica). Solid lines are nonlinear regression fit of data to a pseudo first-order rate equation, as described in “Materials and methods.”