A study on intra-particle diffusion effects in enzymatic reactions: glucose-fructose isomerization

In this work different aspects of the glucose-fructose enzymatic isomerization, using immobilized glucose isomerase, are studied and quantified. Reaction temperatures range from 40 degrees C to 60 degrees C. Intra-particle effective diffusivities (D-e), determined after uptake experiments, are between 1.20 x 10(-6) cm(2)/s, at 40 degrees C, and 2.52 x 10(-6) cm(2)/s, at 60 degrees C. The estimated energy of activation for diffusion (E-aD) is 7.71 kcal/mol. No significant adsorption of the sugars on the support gel matrix is observed. Crushed particles (phi = 150-350 mu) are used during kinetic experiments. For this range of particle diameters, inherent kinetics is approached. A reversible Michaelis-Menten rate equation is fitted to the data, providing the following parameters at pH = 7.0: k(0) = 2.15 x 10(-6) g/IU/s; E-a/R = 8998 K. Glucose (K-G) and fructose (K-F) affinity constants are essentially the same, ranging from 0.190 M, at 40 degrees C to 0.305 M, at 60 degrees C. The thermodynamic equilibrium constant is determined for the three temperatures, and the heat of reaction, estimated from a Van't Hoff plot, is Delta H = 1682 cal/mol. Independent experiments, where the reaction occurs in the presence of significant intra-particle mass transfer resistance, are used as validation tests.