Figure 4. Kinetics of intrinsic tenase on activated platelets.

(A) Dependence of the initial rate of fX activation on concentration of thrombin-activated platelets. Theoretical dependence (solid curve) is obtained using Model 2 (eqns A60, A57, A58 and A59). The values of the constants are listed in Table 2. The conditions of the experiment were 500 nM fX, 50 nM fIXa, 0.1 nM fVIIIa and increasing concentrations of platelets. From Rosing, J., van Rijn, J. L., Bevers, E. M., van Dieijen, G., Comfurius, P. and Zwaal, R. F. (1985) The role of activated human platelets in prothrombin and factor X activation. Blood 65, 319–332. Copyright American Society of Haematology, used with permission. (B) Dependence of the apparent V_max (▪) and the apparent K_m (○) of fX activation by the intrinsic tenase on concentration of thrombin-activated platelets. The calculations were carried out using Model 2 (eqns A60, A57, A58 and A59). The values of the constants are listed in Table 2. The conditions of the simulation were 0.1 nM fIXa, 5 nM fVIIIa and increasing concentrations of platelets. To find V_max and K_m, the rate of fXa production is calculated at 5, 10, 20, 50 and 100 nM of fX, and dependence of the activation rate on fX concentration is approximated with the non-linear least-squares method (see the Materials and methods section). The solid lines are drawn with the help of B-spline interpolation.