Stoner C D
Department of Surgery, Ohio State University, Columbus 43210.
Biochem J. 1993 Apr 15;291 ( Pt 2)(Pt 2):585-93. doi: 10.1042/bj2910585.
Methods are given whereby the steady-state kinetic characteristics of multienzyme reactions consisting of individual single-enzyme reactions linked by freely diffusible intermediates can be determined quantitatively from the experimentally determined complete algebraic rate equations for the individual reactions. The approach is based on the fact that a valid steady-state rate equation for such a multienzyme reaction, in terms of the rate equations for the individual reactions, can be obtained simply from knowledge of the relative rates of the individual reactions when the multienzyme reaction is in the steady state. A number of model multienzyme reactions, which differ as to structural arrangement of the individual reactions, are examined by this approach. Simple mathematical methods which are applicable to most of these models are given for direct calculation of dependent variables. It is either pointed out or demonstrated with Mathematica that the rate equations for all of these models can be handled very easily with the aid of a personal computer equipped with appropriate equation-solving software. Since the approach permits evaluation of all dependent variables for any specific combination of values for the kinetic parameters and independent variables, numerical values for the flux control coefficients of the individual enzymes can be obtained by direct calculation for a wide variety of conditions and can be compared with those obtained according to the methods of Metabolic Control Analysis. Several such comparisons have been made and in all cases identical results were obtained. The intuitive notion that the individual enzymes of a multienzyme reaction would be equally rate limiting if the total amount of enzyme were being used with maximum efficiency is tested and shown to be incorrect. In the course of this test the flux control coefficient for the individual enzymes were found to be appropriate indicators of relative rate limitation or control by the enzymes and to account properly for differences in specific activity among the enzymes.
文中给出了一些方法，通过这些方法，可以根据实验测定的各个单酶反应的完整代数速率方程，定量地确定由可自由扩散的中间体连接的单酶反应组成的多酶反应的稳态动力学特征。该方法基于这样一个事实：对于这样一个多酶反应，就各个反应的速率方程而言，一个有效的稳态速率方程可以简单地从多酶反应处于稳态时各个反应的相对速率的知识中获得。通过这种方法研究了一些模型多酶反应，这些反应在各个反应的结构排列上有所不同。给出了适用于这些模型中大多数的简单数学方法，用于直接计算因变量。文中指出或用Mathematica证明，借助配备适当方程求解软件的个人计算机，可以非常容易地处理所有这些模型的速率方程。由于该方法允许评估动力学参数和自变量的任何特定值组合的所有因变量，因此可以通过直接计算在各种条件下获得各个酶的通量控制系数的数值，并将其与根据代谢控制分析方法获得的数值进行比较。已经进行了几次这样的比较，在所有情况下都得到了相同的结果。对多酶反应中各个酶如果以最大效率使用酶总量时将同样成为速率限制因素这一直观概念进行了检验，并证明是不正确的。在这个检验过程中，发现各个酶的通量控制系数是酶相对速率限制或控制的合适指标，并且能够恰当地解释酶之间比活性的差异。
