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. 1995 Aug;69(2):362–371. doi: 10.1016/S0006-3495(95)79908-8

Surface-mediated enzymatic reactions: simulations of tissue factor activation of factor X on a lipid surface.

R Gentry 1, L Ye 1, Y Nemerson 1
PMCID: PMC1236260  PMID: 8527649

Abstract

Blood coagulation proceeds via reactions in which zymogen coagulation factors are activated to proteases. An essential step is the activation of factor X by a complex of tissue factor and factor VIIa. This complex usually is studied using phospholipid vesicles into which tissue factor is inserted. Because factor X exists free in solution and bound to the lipid-surface, it is difficult to establish experimentally the kinetic contribution of surfaces. We therefore developed a stochastic model to simulate such reactions and generate initial velocity data from which Michaelis-Menten parameters are estimated. Simulated Km values decrease slightly when substrate binding to lipid is increased and by a factor of four when the rates of surface diffusion are increased to that of fluid phase-diffusion. Simulations with various size planar surfaces established an enzyme capture radius of 32-64 nm. Simulations with different modes of enzyme-substrate complex assembly show that if the true substrate is lipid-bound, under certain conditions, the true Kcat is not measured; rather, the product "leaving rate" from the complex is the rate-limiting step that is measured as substrate is taken to infinity. This model is applicable to any surface-bound enzyme reaction.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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