Gentry R, Ye L, Nemerson Y
Department of Mathematics and Statistics, University of Guelph, Ontario, Canada.
Biophys J. 1995 Aug;69(2):356-61. doi: 10.1016/S0006-3495(95)79907-6.
Many in vivo enzymatic processes, such as those of the tissue factor pathway of blood coagulation, occur in environments with facilitated substrate delivery or enzymes bound to cellular or lipid surfaces, which are quite different from the ideal fluid environment for which the Michaelis-Menten equation was derived. To describe the kinetics of such reactions, we propose a microscopic model that focuses on the kinetics of a single-enzyme molecule. This model provides the foundation for macroscopic models of the system kinetics of reactions occurring in both ideal and nonideal environments. For ideal reaction systems, the corresponding macroscopic models thus derived are consistent with the Michaelis-Menten equation. It is shown that the apparent Km is in fact a function of the mechanism of substrate delivery and should be interpreted as the substrate level at which the enzyme vacancy time equals the residence time of ES-complexes; it is suggested that our microscopic model parameters characterize more accurately an enzyme and its catalytic efficiency than does the classical Km. This model can also be incorporated into computer simulations of more complex reactions as an alternative to explicit analytical formulation of a macroscopic model.
许多体内酶促过程，如凝血组织因子途径的那些过程，发生在底物传递便利或酶与细胞或脂质表面结合的环境中，这与推导米氏方程所依据的理想流体环境大不相同。为了描述此类反应的动力学，我们提出了一个微观模型，该模型聚焦于单个酶分子的动力学。此模型为理想和非理想环境中发生的反应的系统动力学宏观模型提供了基础。对于理想反应系统，由此推导的相应宏观模型与米氏方程一致。结果表明，表观Km实际上是底物传递机制的函数，应解释为酶空时等于ES复合物停留时间时的底物水平；有人认为，与经典的Km相比，我们的微观模型参数能更准确地表征一种酶及其催化效率。该模型也可纳入更复杂反应的计算机模拟中，作为宏观模型显式解析公式的替代方法。
