title: Hidden Reaction: Mesophilic Cellobiose 2-Epimerases Produce Lactulose.
abstract: Lactulose (4-O-β-d-galactopyranosyl-d-fructofuranose) is a prebiotic sugar derived from the milk sugar lactose (4-O-β-d-galactopyranosyl-d-glucopyranose). In our study we observed for the first time that known cellobiose 2-epimerases (CEs; EC 5.1.3.11) from mesophilic microorganisms were generally able to catalyze the isomerization reaction of lactose into lactulose. Commonly, CEs catalyze the C2-epimerization of d-glucose and d-mannose moieties at the reducing end of β-1,4-glycosidic-linked oligosaccharides. Thus, epilactose (4-O-β-d-galactopyranosyl-d-mannopyranose) is formed with lactose as substrate. So far, only four CEs, exclusively from thermophilic microorganisms, have been reported to additionally catalyze the isomerization reaction of lactose into lactulose. The specific isomerization activity of the seven CEs in this study ranged between 8.7 ± 0.1 and 1300 ± 37 pkat/mg. The results indicate that very likely all CEs are able to catalyze both the epimerization as well as the isomerization reaction, whereby the latter is performed at a comparatively much lower reaction rate.
authors.affiliation: Department of Biotechnology and Enzyme Science, Institute of Food Science and Biotechnology, University of Hohenheim , Garbenstrasse 25, D-70599, Stuttgart, Germany.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Kuschel
authors.affiliation: Department of Biotechnology and Enzyme Science, Institute of Food Science and Biotechnology, University of Hohenheim , Garbenstrasse 25, D-70599, Stuttgart, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Seitl
authors.affiliation: Department of Biotechnology and Enzyme Science, Institute of Food Science and Biotechnology, University of Hohenheim , Garbenstrasse 25, D-70599, Stuttgart, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Glück
authors.affiliation: State Key Laboratory of Food Science and Technology, Jiangnan University , Wuxi, Jiangsu 214122, China.
authors.forename: Wanmeng
authors.identifier: http://orcid.org/0000-0001-6597-527X
authors.initials: W
authors.lastname: Mu
authors.affiliation: State Key Laboratory of Food Science and Technology, Jiangnan University , Wuxi, Jiangsu 214122, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.affiliation: Department of Biotechnology and Enzyme Science, Institute of Food Science and Biotechnology, University of Hohenheim , Garbenstrasse 25, D-70599, Stuttgart, Germany.
authors.forename: Timo
authors.identifier: http://orcid.org/0000-0001-9392-4031
authors.initials: T
authors.lastname: Stressler
authors.affiliation: Department of Biotechnology and Enzyme Science, Institute of Food Science and Biotechnology, University of Hohenheim , Garbenstrasse 25, D-70599, Stuttgart, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Fischer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001439:Bacteroides / Q000201:enzymology / Q000235:genetics; D055162:Biocatalysis; D002238:Carbohydrate Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002475:Cellobiose / Q000737:chemistry / Q000378:metabolism*; D004795:Enzyme Stability; D005417:Flavobacterium / Q000201:enzymology / Q000235:genetics; D007785:Lactose / Q000378:metabolism; D007792:Lactulose / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002475:Cellobiose; D007792:Lactulose; D002238:Carbohydrate Epimerases; D007785:Lactose
keywords: RaCE; cellobiose 2-epimerase; epimerization; isomerization; lactose; lactulose