Laboratory of Thermodynamics, Department of Biochemical and Chemical Engineering, Technische Universitaet Dortmund, Emil-Figge-Str. 70, 44227 Dortmund, Germany.
Laboratory of Thermodynamics, Department of Biochemical and Chemical Engineering, Technische Universitaet Dortmund, Emil-Figge-Str. 70, 44227 Dortmund, Germany.
Biophys Chem. 2020 Mar;258:106330. doi: 10.1016/j.bpc.2020.106330. Epub 2020 Jan 13.
The glycolytic pathway is present in most organisms and represents a central part of the energy production mechanism in a cell. For a general understanding of glycolysis, the investigation from a thermodynamic point of view is essential and allows realising thermodynamic feasibility analyses under in vivo conditions. However, available literature standard Gibbs energies of reaction, Δg', are calculated using equilibrium-molality ratios K', which might lead to a misinterpretation of the glycolytic pathway. It was the aim of this work to thermodynamically investigate the triosephosphate isomerase (TPI) reaction to provide new activity-based reaction data. In vitro equilibrium experiments were performed, and activity coefficients were predicted with the equation of state electrolyte PC-SAFT (ePC-SAFT). The combination of experimental concentrations and predicted activity coefficients yielded the thermodynamic equilibrium constant K and a new value for Δg'(298.15 K, pH 7) = 7.1 ± 0.3 kJ mol. The availability of the new Δg' value allowed predicting influences of the reaction medium on the reaction equilibrium of the TPI reaction. In this work, influences of the initial substrate concentration, pH and Mg concentration on the reaction equilibrium were investigated and a method is presented to predict these influences. The higher the substrate concentration and the higher the temperature, the stronger the reaction equilibrium is shifted on the product side. While the pH did not have a significant influence on the reaction equilibrium, Mg yielded a shift of the reaction equilibrium to the substrate side. All these effects were predicted correctly with ePC-SAFT. Based on the ePC-SAFT predictions we concluded that a charge-reduction of the product by complexation of the product with Mg was responsible for the strong influence of Mg on the reaction equilibrium. Finally, the standard enthalpy of reaction of Δh(pH 7) = 18 ± 7 kJ mol was determined with the equilibrium constants K at 298.15 K, 304.15 K and 310.15 K using the van 't Hoff equation.
糖酵解途径存在于大多数生物体中，是细胞能量产生机制的核心部分。为了全面了解糖酵解，从热力学角度进行研究是必不可少的，这可以实现在体内条件下进行热力学可行性分析。然而，现有的文献标准吉布斯自由能变化，Δg'，是使用平衡摩尔比 K'计算的，这可能导致对糖酵解途径的错误解释。本工作的目的是从热力学上研究磷酸丙糖异构酶（TPI）反应，提供新的基于活性的反应数据。进行了体外平衡实验，并使用状态方程电解质 PC-SAFT（ePC-SAFT）预测了活度系数。实验浓度与预测活度系数的结合产生了热力学平衡常数 K 和新的Δg'（298.15 K，pH 7）= 7.1 ± 0.3 kJ mol。新的Δg'值的可用性允许预测反应介质对 TPI 反应平衡的影响。在这项工作中，研究了初始底物浓度、pH 和 Mg 浓度对反应平衡的影响，并提出了一种预测这些影响的方法。底物浓度和温度越高，产物侧的反应平衡就越强。虽然 pH 对反应平衡没有显著影响，但 Mg 会使反应平衡向底物侧转移。所有这些影响都被 ePC-SAFT 正确预测。基于 ePC-SAFT 的预测，我们得出结论，产物通过与 Mg 络合而发生电荷还原是 Mg 对反应平衡产生强烈影响的原因。最后，使用平衡常数 K 在 298.15 K、304.15 K 和 310.15 K 下，根据 van't Hoff 方程，用 ePC-SAFT 预测确定了标准焓变Δh（pH 7）= 18 ± 7 kJ mol。
