Giersch C
Institut für Botanik der Technischen Hochschule Darmstadt, Germany.
Eur J Biochem. 1995 Aug 1;231(3):587-92.
An established method to determine flux control coefficients is the enzyme titration method in which the change in pathway flux upon a change in the enzyme concentration is measured. In this study, the application of this method to a simple reconstituted pathway was investigated by simulated measurements. The pathway was assumed to be in the quasi-steady-state, which is the experimental realization of the mathematical construct 'steady state'. It was shown that flux control coefficients, calculated in a way that mimics their experimental determination, were strongly time dependent. Initially, the calculated flux control coefficient was high for the enzyme adjacent to the reaction monitoring the flux, and the steady-state value was overestimated. Likewise, flux control coefficients were underestimated for enzymes further away from the monitoring reaction. The observed time course of simulated flux control coefficients was shown to reflect the fact that experimental systems are not steady state but quasi-steady-state. For a pathway in the quasi-steady-state, some of the problems with enzyme titration experiments can be overcome by allowing the system to relax for a time interval that is large compared with the turnover time of the pooled pathway intermediates.
一种确定通量控制系数的既定方法是酶滴定法，即测量酶浓度变化时途径通量的变化。在本研究中，通过模拟测量研究了该方法在简单重构途径中的应用。该途径被假定处于准稳态，这是数学概念“稳态”的实验实现。结果表明，以模拟实验测定方式计算出的通量控制系数强烈依赖于时间。最初，对于紧邻监测通量的反应的酶，计算出的通量控制系数较高，且稳态值被高估。同样，对于远离监测反应的酶，通量控制系数被低估。模拟通量控制系数的观测时间进程表明，实验系统不是稳态而是准稳态。对于处于准稳态的途径，通过使系统在与合并的途径中间体周转时间相比足够长的时间间隔内弛豫，可以克服酶滴定实验中的一些问题。
