Analysis of the kinetics of factor X activation by tissue factor-factor VIIA.

In this paper we consider the assumptions that apply to the classical Michaelis-Menten enzyme kinetics and examine their applicability to a two-dimensional catalytic system. While we specifically address the kinetics of factor X activation catalyzed by a complex of tissue factor and factor VIIa, these concepts are applicable to any system in which both enzyme and substrate are membrane-bound. We emphasize the fact that the membranes become crowded with substrate and product molecules, thus rendering the assumption of "sparseness" inappropriate. Data from computer simulations are considered as well as preliminary laboratory experiments.