The extraction and mechanism of a novel isomaltulose-synthesizing enzyme from Erwinia rhapontici

Biochem J. 1984 May 15;220(1):213-20. doi: 10.1042/bj2200213.


The single enzyme that mediates the bioconversion is demonstrated to be located in the cells' periplasmic space, a site that facilitates its use as an industrial biocatalyst, and to be a previously undescribed hexosyltransferase with four novel features. The enzyme is sucrose-specific, and has an intramolecular mechanism in which both glucose and fructose residues appear to be enzyme-bound. Thirdly, it is reaction-non-selective, forming simultaneously isomaltulose and a second hitherto uncharacterized alpha-(1----1)-linked disaccharide (trehalulose), by hydrolysis of sucrose followed by reaction of glucose with the C-6 and C-1 positions of the fructofuranose respectively. Finally, on extended incubation an unusual recycling mechanism caused the concentration of isomaltulose, the kinetically preferred product, to reach a transient maximum concentration and then fall, and the concentration of trehalulose, the thermodynamically favoured product, to rise slowly.

MeSH terms

  • Carbohydrate Epimerases / isolation & purification
  • Carbohydrate Epimerases / metabolism*
  • Chemical Phenomena
  • Chemistry
  • Chromatography, Thin Layer
  • Disaccharides / biosynthesis
  • Erwinia / enzymology*
  • Fructose / metabolism
  • Glucose / metabolism
  • Hexosyltransferases
  • Intramolecular Transferases*
  • Isomaltose / analogs & derivatives
  • Isomaltose / biosynthesis
  • Substrate Specificity
  • Sucrose / metabolism


  • Disaccharides
  • Fructose
  • Sucrose
  • Isomaltose
  • Hexosyltransferases
  • Carbohydrate Epimerases
  • Intramolecular Transferases
  • isomaltulose synthase
  • trehalulose
  • Glucose
  • isomaltulose