title: Characterization of a novel beta-galactosidase from Bifidobacterium adolescentis DSM 20083 active towards transgalactooligosaccharides.
abstract: This paper reports on the effects of both reducing and nonreducing transgalactooligosaccharides (TOS) comprising 2 to 8 residues on the growth of Bifidobacterium adolescentis DSM 20083 and on the production of a novel beta-galactosidase (beta-Gal II). In cells grown on TOS, in addition to the lactose-degrading beta-Gal (beta-Gal I), another beta-Gal (beta-Gal II) was detected and it showed activity towards TOS but not towards lactose. beta-Gal II activity was at least 20-fold higher when cells were grown on TOS than when cells were grown on galactose, glucose, and lactose. Subsequently, the enzyme was purified from the cell extract of TOS-grown B. adolescentis by anion-exchange chromatography, adsorption chromatography, and size-exclusion chromatography. Beta-Gal II has apparent molecular masses of 350 and 89 kDa as judged by size-exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively, indicating that the enzyme is active in vivo as a tetramer. Beta-Gal II had an optimal activity at pH 6 and was not active below pH 5. Its optimum temperature was 35 degrees C. The enzyme showed highest V(max) values towards galactooligosaccharides with a low degree of polymerization. This result is in agreement with the observation that during fermentation of TOS, the di- and trisaccharides were fermented first. Beta-Gal II was active towards beta-galactosyl residues that were 1-->4, 1-->6, 1-->3, and 1 <--> 1 linked, signifying its role in the metabolism of galactooligosaccharides by B. adolescentis.
authors.affiliation: Laboratories for Food Chemistry, Department of Food Technology and Nutritional Sciences, Wageningen University, Wageningen, The Netherlands.
authors.forename: K M
authors.initials: KM
authors.lastname: Van Laere
authors.forename: T
authors.initials: T
authors.lastname: Abee
authors.forename: H A
authors.initials: HA
authors.lastname: Schols
authors.forename: G
authors.initials: G
authors.lastname: Beldman
authors.forename: A G
authors.initials: AG
authors.lastname: Voragen
mesh_terms: D001644:Bifidobacterium / Q000201:enzymology* / Q000254:growth & development; D003470:Culture Media; D005690:Galactose; D007700:Kinetics; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D003470:Culture Media; D009844:Oligosaccharides; D001616:beta-Galactosidase; D005690:Galactose