title: Characterization and molecular cloning of a heterodimeric beta-galactosidase from the probiotic strain Lactobacillus acidophilus R22.
abstract: Beta-galactosidase from the probiotic strain Lactobacillus acidophilus R22 was purified to apparent homogeneity by ammonium sulphate fractionation, hydrophobic interaction, and affinity chromatography. The enzyme is a heterodimer consisting of two subunits of 35 and 72 kDa, as determined by gel electrophoresis. The optimum temperature of beta-galactosidase activity was 55 degrees C (10-min assay) and the range of pH 6.5-8, respectively, for both o-nitrophenyl-beta-D-galactopyranoside (oNPG) and lactose hydrolysis. The Km and Vmax values for lactose and oNPG were 4.04+/-0.26 mM, 28.8+/-0.2 micromol D-glucose released per min per mg protein, and 0.73+/-0.07 mM, 361+/-12 micromol o-nitrophenol released per min per mg protein, respectively. The enzyme was inhibited by high concentrations of oNPG with Ki,s=31.7+/-3.5 mM. The enzyme showed no specific requirements for metal ions, with the exception of Mg2+, which enhanced both activity and stability. The genes encoding this heterodimeric enzyme, lacL and lacM, were cloned, and compared with other beta-galactosidases from lactobacilli. Beta-galactosidase from L. acidophilus was used for the synthesis of prebiotic galacto-oligosaccharides (GOS) from lactose, with the maximum GOS yield of 38.5% of total sugars at about 75% lactose conversion.
authors.affiliation: Research Centre Applied Biocatalysis, Petersgasse, Graz, Austria.
authors.forename: Thu-Ha
authors.initials: TH
authors.lastname: Nguyen
authors.forename: Barbara
authors.initials: B
authors.lastname: Splechtna
authors.forename: Stanimira
authors.initials: S
authors.lastname: Krasteva
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kneifel
authors.forename: Klaus D
authors.initials: KD
authors.lastname: Kulbe
authors.forename: Christina
authors.initials: C
authors.lastname: Divne
authors.forename: Dietmar
authors.initials: D
authors.lastname: Haltrich
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D003001:Cloning, Molecular; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007779:Lactobacillus acidophilus / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D019936:Probiotics; D020539:Sequence Analysis, Protein; D013696:Temperature; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002412:Cations; D009844:Oligosaccharides; D001616:beta-Galactosidase