The extraction and mechanism of a novel isomaltulose-synthesizing enzyme from Erwinia rhapontici.
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.
D002238:Carbohydrate Epimerases / Q000302:isolation & purification / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D002855:Chromatography, Thin Layer; D004187:Disaccharides / Q000096:biosynthesis; D004885:Erwinia / Q000201:enzymology*; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006602:Hexosyltransferases; D019751:Intramolecular Transferases; D007534:Isomaltose / Q000031:analogs & derivatives / Q000096:biosynthesis; D013379:Substrate Specificity; D013395:Sucrose / Q000378:metabolism
D004187:Disaccharides; D005632:Fructose; D013395:Sucrose; D007534:Isomaltose; D006602:Hexosyltransferases; D002238:Carbohydrate Epimerases; D019751:Intramolecular Transferases; C042002:isomaltulose synthase; C042003:trehalulose; D005947:Glucose; C008189:isomaltulose