Isomerization of D-Glucose with Glucose-isomerase. A Mechanistic Study.

Abstract

The isomerization of D-glucose to D-fructose by the enzyme glucose-isomerase proceeds without participation of solvent molecules for a soluble as well as an immobilized form of the enzyme. The stereospecificity of the enzymatic reaction was determined using D-glucose labeled with deuterium in the 1- or 2-position, respectively. Both are isomerized to D-fructose labeled with 2H at C-1, the former with the 1S configuration and the latter with the 1R configuration. The reaction was followd by 2H and 13C NMR spectroscopy; both .alpha.-D-glucopyranose and .beta.-D-fructofuranose are substrates for the enzyme. In addition, the substrate specificity for the immobilized enzyme was investigated and it was shown that 3-, 5- and 6-deoxy-D-glucose together with 3-0- and 6-0-methyl-D-glucose are substrates for the enzyme, whereas 4-deoxy- and 4-O-methyl-D-glucose cannot be isomerized.