Influence of cytosolic conditions on the reaction equilibrium and the reaction enthalpy of the enolase reaction accessed by calorimetry and van ‘t HOFF

Thermodynamics and Kinetics of Glycolytic Reactions. Part II: Influence of Cytosolic Conditions on Thermodynamic State Variables and Kinetic Parameters

“…At the highest concentration of crowding agents (250 g kg −1 ) the reaction enthalpy change decreased to 70 ± 3% (PEG 20,000), to 69 ± 1% (PEG 6000) and to 66 ± 9% (BSA). The influence of cytosolic conditions on the reaction enthalpy change of reaction 9 has already been investigated in a previous paper where we also showed that cytosolic conditions have a strong effect on the reaction enthalpy change, especially pH, high sodium ion concentration and crowding [6]. When comparing the results of both reactions, it is noticeable that the change in pH value and the introduction of crowding agents had the greatest influence on the reaction enthalpy change.…”

“…The increase of the PEG concentration to 250 g kg −1 for PEG 20.000 or PEG 6000 and a BSA concentration of 250 g kg −1 did not change the reaction enthalpy change significantly compared to 113 g kg −1 . The influence of the cytosolic conditions on the reaction enthalpy change of reaction 9 was different for some conditions (Table S4 in supplementary materials) [6]. A reaction enthalpy change of 2.4 ± 0.1 kJ mol −1 was determined under basic conditions.…”

“…Unfortunately the reasons for this result were not discussed in the respective publications. Three explanations for the influence of PEG are imaginable [6]. The Gibbs free energy change of the reaction (∆ R G) is composed of the reaction enthalpy change and the entropy change (Equation 7in the Section 4).…”

“…Kinetic investigations, especially for glycolytic reactions, can be found in the literature in large numbers. Some of these reactions have been monitored using calorimetry [1][2][3][4][5][6]. Isothermal titration calorimetry (ITC) is well suited for such measurements.…”

“…The influence of macromolecular crowding is worth mentioning in particular, as cells contain between 200 and 300 g L −1 of proteins [28]. Therefore, it is not surprising that this influence can significantly change both the thermodynamic state variables and kinetic parameters of the reactions [3,6,29] compared to pure buffer solutions. Another important factor that has often been neglected is the reversibility of some glycolytic reactions.…”