Qian Hong, Elson Elliot L
Department of Applied Mathematics, University of Washington, Seattle, WA 98195, USA.
Proc Natl Acad Sci U S A. 2004 Mar 2;101(9):2828-33. doi: 10.1073/pnas.0305962101. Epub 2004 Feb 17.
In living cells, biochemical reaction networks often function in nonequilibrium steady states. Under these conditions, the networks necessarily have cyclic reaction kinetics that are maintained by sustained constant input and output, i.e., pumping. To differentiate this state from an equilibrium state without flux, we propose a microscopic method based on concentration fluctuation measurements, via fluorescence correlation spectroscopy, and statistical analyses of high-order correlations and cross correlations beyond the standard fluorescence correlation spectroscopy autocorrelation. We show that, for equilibrium systems with time reversibility, the correlation functions possess certain symmetries, the violation of which is a measure of steady-state fluxes in reaction cycles. This result demonstrates the theoretical basis for experimentally measuring reaction fluxes in a biochemical network in situ and the importance of single-molecule measurements in providing fundamental information on nonequilibrium steady-states in biochemistry.
在活细胞中，生化反应网络通常在非平衡稳态下发挥作用。在这些条件下，网络必然具有循环反应动力学，这种动力学通过持续的恒定输入和输出（即泵浦）来维持。为了将这种状态与无通量的平衡状态区分开来，我们提出了一种微观方法，该方法基于通过荧光相关光谱法进行的浓度波动测量，以及对超出标准荧光相关光谱自相关的高阶相关性和交叉相关性的统计分析。我们表明，对于具有时间可逆性的平衡系统，相关函数具有某些对称性，而这些对称性的违背是反应循环中稳态通量的一种度量。这一结果证明了原位实验测量生化网络中反应通量的理论基础，以及单分子测量在提供生物化学中非平衡稳态基本信息方面的重要性。
