A thermodynamic investigation of the glucose-6-phosphate isomerization

Abstract

In this work, ΔRg+ values for the enzymatic G6P isomerization were determined as a function of the G6P equilibrium molality between 25°C and 37°C. The reaction mixtures were buffered at pH=8.5. In contrast to standard literature work, ΔRg+ values were determined from activity-based equilibrium constants instead of molality-based apparent values. This yielded a ΔRg+ value of 2.55±0.05kJmol−1 at 37°C, independent of the solution pH between 7.5 and 8.5. Furthermore, ΔRh+ was measured at pH=8.5 and 25°C yielding 12.05±0.2kJmol−1.Accounting for activity coefficients turned out to influence ΔRg+ up to 30% upon increasing the G6P molality. This result was confirmed by predictions using the thermodynamic model ePC-SAFT.Finally, the influence of the buffer and of potassium glutamate as an additive on the reaction equilibrium was measured and predicted with ePC-SAFT in good agreement.