Kinetics of the Inhibitory Effect of Factor IXBm in the Activation of Factor X by Factor VII and Bovine Tissue Factor

B. Østerud, C.K. Kasper, S.I. Rapaport
1979 VIIth International Congress on Thrombosis and Haemostasis   unpublished
F.IXBm is giving a prolonged prothrombin time with bovine tissue factor (T.F.). In the present study the inhibitory effect of purified F.IXBm was tested in a F.VII assay that measures the ability of F.VII to activate F.X in the presence of bovine T.F. and Ca++, followed by the quantitation of formed F.Xa by the synthetic substrate benzoyl -L-Ile-Glu-Gly-L-Arg-p-nitroanilide. Experiments were carried out with different concentrations of F.IXBm and F.X, keeping the concentrations of F.VII and
more » ... ne T.F. constant. Lineweaver-Burk plot of the data showed that all the curves crossed the l/V axis in one point - no inhibition by F.IXBm at infinite concentratlons of F.X. Thus, F.IXBm acts as competitive in inhibitor to F.X in the activation of F.X by F.VII and bovine T.F. By plotting the 1/V against the inhibitor concentrations (F.IXBm conc), a Dixon plot, the Ki for F.IXBm was determined to be 0.017 μM.Normal F.IX was also found to be a competitive inhibitor to F.X but 4-5 times higher concentrations of F.IX were needed to give the same inhibition as F.IXBm. Utilizing human T.F. instead of bovine T.F. in this assay resulted in no significant inhibition by either F.IX of F.IXBm.
doi:10.1055/s-0039-1684667 fatcat:iawase55ibagzod4fqwgfkxemy