posted on 2017-03-02, 00:00authored byBeatrice Kuschel, Ines Seitl, Claudia Glück, Wanmeng Mu, Bo Jiang, Timo Stressler, Lutz Fischer
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.