alexa Characterization and molecular cloning of a heterodimeric β-galactosidase from the probiotic strain Lactobacillus acidophilus R22


Journal of Food & Industrial Microbiology

Author(s): ThuHa Nguyen, Barbara Splechtna, Stanimira Krasteva, Wolfgang Kneifel, Klaus D Kulbe, Christina Divne, Dietmar Haltrich

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b -Galactosidase from the probiotic strain Lactobacillus acidophilus R22 was purified to apparent homogeneity by ammonium sulphate fractionation, hydro- phobic 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 b -galactosidase activity was 55 1 C (10-min assay) and the range of pH 6.5–8, respectively, for both o -nitrophenyl- b - D -galactopyr- anoside ( o NPG) and lactose hydrolysis. The K m and V max values for lactose and o NPG were 4.04  0.26 mM, 28.8  0.2 m mol D -glucose released per min per mg protein, and 0.73  0.07 mM, 361  12 m mol o -nitrophenol released per min per mg protein, respectively. The enzyme was inhibited by high concentrations of o NPG with K i,s = 31.7  3.5 mM. The enzyme showed no specific requirements for metal ions, with the exception of Mg 2 1 , which enhanced both activity and stability. The genes encoding this heterodimeric enzyme, lacL and lacM , were cloned, and compared with other b -galactosidases from lactobacilli. b -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.

This article was published in Microbiology Letters and referenced in Journal of Food & Industrial Microbiology

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