Characteristics of a Bifidobacterium longum LL04 beta-galactosidase (recombinant) produced in Escherichia coli

Abstract

Recombinant beta-galactosidase from Bifidobacterium longum LL04 was expressed in Escherichia coli and partially purified by ammonium sulphate precipitation and anion-exchange chromatography (Mono-Q). The optimum temperature and pH of the partially purified enzyme were 50 degrees C and pH 7.0-8.0, respectively, when o-nitrophenyl-beta-D-galactopyranoside was used as a substrate. The enzyme was stable over the pH range of 5.0-9.0, and was active at 40 degrees C for more than 60 min at pH 7.0. The enzyme was significantly activated by Na+ and K+. Maximal activity was observed at the concentration of 10 mM for both Na+ and K+. The enzyme activity was strongly inhibited by most bivalent metal ions. The Kin and Vmax on ONPG at 37 and 50 degrees C were 0.72, 167.9, and 0.507 mM, 310.9 U/mL, respectively.