The influence of enzyme immobilization on the main thermodynamic quantities of glucose isomerization to fructose and vice versa was studied in batch tests by using a commercial immobilized glucose isomerase. The values calculated for the immobilized system showed, when compared with those reported for the native enzyme, higher equilibrium constants at T > 70 degrees C and simultaneous increases in both standard enthalpy and entropy changes of reaction. Activation enthalpy and entropy changes of both forward and reverse enzyme-catalyzed reactions were calculated from the initial glucose isomerase activity evaluated at different temperatures by the Briggs-Haldane model. The activation enthalpy of the forward reaction was about 24% less than that of the native enzyme. Enzyme inactivation tests performed at different temperatures and sugar equilibrium concentrations confirmed the existence of the so-called substrate protection phenomenon which resulted in a 29-36% reduction in the decay constant. A slight increase in the activation free enthalpy of the inactivation reaction was also shown.