Purification and Characterization of \beta-Galactosidase from the Streptococcus thermophilus Strain RSKK 667

Authors: Ufuk GÜNDÜZ, Ressa REJAEE

Abstract: 13-Galactosidase (Lactase) was extracted from the Streptococcus thermophilus strain RSKK 667 grown in M 17 medium. The enzyme was purified by acetone and ammonium sulfate fractionation, gel filtration on Sephadex G-200 and ion exchange chromatography on DEAE-Sephadex A-50. Mg{^2+} stimulated the activity while the enzyme was strongly inhibited by EDTA. The K_m and V {_max} for o-nitrophenyl-\beta-D-galactopyranoside (ONPG) as substrate was 0.56 mM and 163 units/mg of protein, respectively. Galactose showed competitive inhibition with a K_i value of 50.9 mM.

Keywords: 13-Galactosidase, Iactase, Streptococcus thermophilus