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 a anomer is a substrate of the glucose isomerase at pH 7.5 and 60 degreesC. 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-HaIdane 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. (C) 2000 Elsevier Science B.V. All rights reserved.