Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
Appl Microbiol Biotechnol. 2011 Feb;89(3):645-54. doi: 10.1007/s00253-010-2862-2. Epub 2010 Sep 18.
The gene encoding homodimeric β-galactosidase (lacA) from Bacillus licheniformis DSM 13 was cloned and overexpressed in Escherichia coli, and the resulting recombinant enzyme was characterized in detail. The optimum temperature and pH of the enzyme, for both o-nitrophenyl-β-D: -galactoside (oNPG) and lactose hydrolysis, were 50°C and 6.5, respectively. The recombinant enzyme is stable in the range of pH 5 to 9 at 37°C and over a wide range of temperatures (4-42°C) at pH 6.5 for up to 1 month. The K(m) values of LacA for lactose and oNPG are 169 and 13.7 mM, respectively, and it is strongly inhibited by the hydrolysis products, i.e., glucose and galactose. The monovalent ions Na(+) and K(+) in the concentration range of 1-100 mM as well as the divalent metal cations Mg²(+), Mn²(+), and Ca²(+) at a concentration of 1 mM slightly activate enzyme activity. This enzyme can be beneficial for application in lactose hydrolysis especially at elevated temperatures due to its pronounced temperature stability; however, the transgalactosylation potential of this enzyme for the production of galacto-oligosaccharides (GOS) from lactose was low, with only 12% GOS (w/w) of total sugars obtained when the initial lactose concentration was 200 g/L.
来自地衣芽孢杆菌 DSM 13 的同源二聚体β-半乳糖苷酶（lacA）的基因被克隆并在大肠杆菌中过表达，所得重组酶得到了详细的表征。该酶的最适温度和 pH 值分别为 50°C 和 6.5，用于 o-硝基苯-β-D：-半乳糖苷（oNPG）和乳糖水解。该重组酶在 pH 5 到 9 范围内在 37°C 下稳定，并且在 pH 6.5 下在 4-42°C 的宽温度范围内稳定长达 1 个月。LacA 对乳糖和 oNPG 的 K(m)值分别为 169 和 13.7 mM，并且被水解产物葡萄糖和半乳糖强烈抑制。单价离子 Na(+)和 K(+)在 1-100 mM 的浓度范围内以及二价金属阳离子 Mg²(+)、Mn²(+)和 Ca²(+)在 1 mM 的浓度下略微激活酶活性。由于其显著的热稳定性，该酶可有益于在乳糖水解中的应用，尤其是在较高温度下；然而，该酶的转半乳糖基化潜力用于从乳糖生产半乳糖低聚糖（GOS）较低，当初始乳糖浓度为 200 g/L 时，仅获得 12%（w/w）的总糖为 GOS。
