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) i s investigated with an immobilized enzyme-packed reactor. A series of isome rization experiments with alpha-, beta-, and equilibrated D-glucose solutio ns indicates that beta anomer as well as a anomer is a substrate of the glu cose 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 a nd 113% higher than beta -D-glucose conversion rate. This anomeric reactivi ty of glucose isomerase is mathematically described with a set of kinetic e quations based on the reaction steps complying with Briggs-HaIdane mechanis m and the experimentally determined kinetic constants. The proposed reactio n mechanism includes the mutarotation and the isomerization reactions of al pha- and beta -D-glucose with different rate constants. (C) 2000 Elsevier S cience B.V. All rights reserved.