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Z. Naturforsch.
69c, 479 – 487
(2015)
doi:10.5560/ZNC.2014-0061
Expression and Characterization of Two β-Galactosidases from Klebsiella pneumoniae 285 in Escherichia coli and their Application in the Enzymatic Synthesis of Lactulose and 1-Lactulose
1 State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China
2 Tianmu College, Zhejiang Agriculture and Forestry University, Zhuji 311800, China
3 School of Food Science and Technology, Jiangnan University, Wuxi 214122, China. Fax: +86-510-85919150. E-mail:
yrj@jiangnan.edu.cn
*Author for correspondence and reprint requests
Received March 16 / October 30, 2014 / published online December 22, 2014
The two genes lacZ1 and lacZ2 from Klebsiella pneumoniae 285, encoding β-galactosidase isoenzymes II and III (KpBGase-II and -III), were each cloned downstream of a T7 promoter for expression in Escherichia coli BL21(DE3), and the resulting recombinant enzymes were characterized in detail. The optimum temperature and pH value of KpBGase-II were 40 °C and 7.5, and those of KpBGase-III were 50 °C and 8.0, respectively. KpBGase-III was more stable than KpBGase-II at higher temperature (>60 °C). Both β-galactosidases were more active towards o-nitrophenyl-β-d-galactopyranoside as compared to lactose. The enzymatic synthesis of lactulose and 1-lactulose catalyzed by KpBGase-II and KpBGase-III was
investigated. Using 400 g/L lactose and 200 g/L fructose as substrates, the resulting lactulose and 1-lactulose yields with KpBGase-II were 6.2 and 42.3 g/L, while those with KpBGase-III were 5.1 and 23.8 g/L, respectively. KpBGase-II has a potential for the production of 1-lactulose from lactose and fructose. Like other β-galactosidases, the two isozymes catalyze the transgalactosylation in the presence of fructose establishing the β-(1→1) linkage.
Key words: Klebsiella pneumoniae, β-Galactosidase, 1-Lactulose