2001/08/31 by Maria P. McGee, Tom Chou
Physics and Astronomy · Biochemistry, Genetics and Molecular Biology · #cond-mat.soft #physics.bio-ph #q-bio.QM
published as J. Biological Chemistry, 276, (2001), 7827-7835 · 6 .eps figs, 25pp
arxiv created 2001/08/31 · arxiv updated 2009/11/30
The initial surface reactions of the extrinsic coagulation pathway on live cell membranes were examined under flow conditions. Generation of fXa (activated coagulation factor X) was measured on spherical monolayers of epithelial cells with a total surface area of 41-47 cm2 expressing TF(tissue factor) at >25 fmol/cm2. Concentrations of reactants and product were monitored as a function of time with radiolabeled proteins and a chromogenic substrate at resolutions of 2-8 s. At physiological concentrations of fVIIa and fX, the reaction rate was 3.05 ± 0.75 fmol fXa/s/cm2, independent of flux, and 10 times slower than that expected for collision-limited reactions. Rates were also independent of surface fVIIa concentrations within the range 0.6-25 fmol/cm2. The transit time of fX activated on the reaction chamber was prolonged relative to transit times of nonreacting tracers or preformed fXa. Membrane reactions were modeled using a set of nonlinear kinetic equations and a lagged normal density curve to track the expected surface concentration of reactants for various hypothetical reaction mechanisms. The experimental results were theoretically predicted only when the models used a slow intermediate reaction step, consistent with surface diffusion. These results provide evidence that the transfer of substrate within the membrane is rate-limiting in the kinetic mechanisms leading to initiation of blood coagulation by the tissue factor pathway.