title: Characterization of β-galactosidase isoforms from Bacillus circulans and their contribution to GOS production.
abstract: A β-galactosidase preparation from Bacillus circulans consists of four isoforms called β-gal-A, β-gal-B, β-gal-C, and β-gal-D. These isoforms differ in lactose hydrolysis and galacto-oligosaccharide (GOS) synthesis at low substrate concentrations. For this reason, using a selection of the isoforms may be relevant for GOS production, which is typically done at high substrate concentrations. At initial lactose concentrations in between 0.44 % and 0.68 % (w/w), β-gal-A showed the least oligosaccharide formation, followed by β-gal-B and β-gal-C; most oligosaccharides were formed by β-gal-D. The differences in behavior were confirmed by studying the thermodynamics of lactose conversion with isothermal titration calorimetry since especially β-gal-A showed a different profile than the other isoforms. Also during the conversion of allolactose and 4-galactosyllactose at 0.44 % and 0.61 % (w/w), respectively, β-gal-A and β-gal-D showed clear differences. In contrast to above findings, the selectivity of the isoforms did hardly differ at an initial lactose concentration of 30 % (w/w), except for a slightly higher production of galactose with β-gal-A. These differences were hypothesized to be related to the different accessibility of the active sites of the isoforms for different-sized reactants. The initial GOS formation rates of the isoforms indicate that β-gal-A and β-gal-B are the best isoforms for GOS production at high lactose concentrations.
authors.affiliation: Food Process Engineering Group, Wageningen University, P.O. Box 8129, 6700 EV, Wageningen, The Netherlands. anja.warmerdam@wur.nl
authors.forename: Anja
authors.initials: A
authors.lastname: Warmerdam
authors.forename: Ekaraj
authors.initials: E
authors.lastname: Paudel
authors.forename: Wanqing
authors.initials: W
authors.lastname: Jia
authors.forename: Remko M
authors.initials: RM
authors.lastname: Boom
authors.forename: Anja E M
authors.initials: AE
authors.lastname: Janssen
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D020134:Catalytic Domain; D004789:Enzyme Activation; D005690:Galactose / Q000378:metabolism; D006868:Hydrolysis; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D008970:Molecular Weight; D013816:Thermodynamics; D014312:Trisaccharides / Q000378:metabolism; D001616:beta-Galactosidase / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007527:Isoenzymes; D014312:Trisaccharides; C001970:allolactose; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose