Kinetics of glucose isomerization to fructose by immobilized glucose isomerase: anomeric reactivity of D-glucose in kinetic model.

The substrate specificity of immobilized D-glucose isomerase (EC 5.3. 1.5) is investigated with an immobilized enzyme-packed reactor. A series of isomerization experiments with alpha-, beta-, and equilibrated D-glucose solutions indicates that beta anomer as well as alpha anomer is a substrate of the glucose isomerase at pH 7.5 and 60 degrees C. For substrate concentration of 0.028 mol l(-1) (1% w/v), the initial conversion rate of alpha-D-glucose was 43% higher than that with equilibrated glucose at the same concentration and 113% higher than beta-D-glucose conversion rate. This anomeric reactivity of glucose isomerase is mathematically described with a set of kinetic equations based on the reaction steps complying with Briggs-Haldane mechanism and the experimentally determined kinetic constants. The proposed reaction mechanism includes the mutarotation and the isomerization reactions of alpha- and beta-D-glucose with different rate constants.