Brand M D
Department of Biochemistry, University of Cambridge, UK.
Mol Cell Biochem. 1998 Jul;184(1-2):13-20.
This paper reviews top-down elasticity analysis, which is a subset of metabolic control analysis. Top-down elasticity analysis provides a systematic yet simple experimental method to identify all the primary sites of action of an effector in complex systems and to distinguish them from all the secondary, indirect, sites of action. In the top-down approach, the complex system (for example, a mitochondrion, cell, organ or organism) is first conceptually divided into a small number of blocks of reactions interconnected by one or more metabolic intermediates. By changing the concentration of one intermediate when all others are held constant and measuring the fluxes through each block of reactions, the overall kinetic response of each block to each intermediate can be established. The concentrations of intermediates can be changed by adding new branches to the system or by manipulating the activities of blocks of reactions whose kinetics are not under investigation. To determine how much an effector alters the overall kinetics of a block of reactions, the overall kinetic response of the block to the intermediate is remeasured in the presence of the effector. Blocks that contain significant primary sites of action will display altered kinetics; blocks that change rate only because of secondary alterations in the concentrations of other metabolites will not. If desired, this elasticity analysis can be repeated with the primary target blocks subdivided into simpler blocks so that the primary sites of action can be defined with more and more precision until, with sufficient subdivision, they are mapped onto individual kinetic steps. Top-down elasticity analysis has been used to identify the targets of effectors of oxygen consumption in mitochondria, hepatocytes and thymocytes. Effectors include poisons such as cadmium and hormones such as triiodothyronine. However, the method is more general than this; in principle it can be applied to any metabolic or other steady-state system.
本文回顾了自上而下的弹性分析，它是代谢控制分析的一个子集。自上而下的弹性分析提供了一种系统而简单的实验方法，用于识别复杂系统中效应物的所有主要作用位点，并将它们与所有次要的、间接的作用位点区分开来。在自上而下的方法中，首先将复杂系统（例如线粒体、细胞、器官或生物体）在概念上划分为少量由一种或多种代谢中间体相互连接的反应模块。当所有其他中间体的浓度保持不变时，通过改变一种中间体的浓度并测量通过每个反应模块的通量，可以确定每个模块对每种中间体的整体动力学响应。中间体的浓度可以通过向系统中添加新的分支或通过操纵其动力学未被研究的反应模块的活性来改变。为了确定效应物对一个反应模块的整体动力学有多大影响，在效应物存在的情况下重新测量该模块对中间体的整体动力学响应。包含重要主要作用位点的模块将显示出改变的动力学；仅由于其他代谢物浓度的次要变化而改变速率的模块则不会。如果需要，可以将主要目标模块进一步细分为更简单的模块，重复这种弹性分析，以便越来越精确地定义主要作用位点，直到经过足够的细分后，它们被映射到各个动力学步骤上。自上而下的弹性分析已被用于识别线粒体、肝细胞和胸腺细胞中氧气消耗效应物的靶点。效应物包括镉等毒物和三碘甲状腺原氨酸等激素。然而，该方法的应用更为广泛；原则上它可以应用于任何代谢或其他稳态系统。
