Abstract：
A novel β-galactosidase gene (PbBgal35A) from Pedobacter sp. CAUYN2 was cloned and expressed in Escherichia coli. The gene had an open reading frame of 1917 bp, encoding 638 amino acids with a predicted molecular mass of 62.3 kDa. The deduced amino acid sequence of the gene shared the highest identity of 41% with a glycoside hydrolase family 35 β-galactosidase from Xanthomonas campestris pv. campestris (AAP86763.1). The recombinant β-galactosidase (PbBgal35A) was purified to homogeneity with a specific activity of 65.9 U/mg. PbBgal35A was optimally active at pH 5.0 and 50 °C, respectively, and it was stable within pH 4.5‒7.0 and up to 45 °C. PbBgal35A efficiently synthesized galacto-oligosaccharides from lactose with a conversion ratio of 32% (w/w) and fructosyl-galacto-oligosaccharides from lactulose with a conversion ratio of 21.9% (w/w). Moreover, the enzyme catalyzed the synthesis of galacto-oligosaccharides from low-content lactose in fresh milk, and the GOS conversion ratios of 17.1% (w/w) and 7.8% (w/w) were obtained when the reactions were performed at 45 and 4 °C, respectively. These properties make PbBgal35A an ideal candidate for commercial use in the manufacturing of GOS-enriched dairy products.
摘要：
一种新的β-半乳糖苷酶基因（PbBgal35A）。克隆CAUYN2并在大肠杆菌中表达。该基因的开放阅读框为1917bp，编码638个氨基酸，预测分子量为62.3kDa。该基因的推导氨基酸序列与来自油菜黄单胞菌pv的糖苷水解酶家族35β-半乳糖苷酶具有41％的最高同一性。樟脑(AAP86763.1)。将重组β-半乳糖苷酶(PbBgal35A)纯化至均一,比活性为65.9U/mg。PbBgal35A在pH5.0和50°C下具有最佳活性，分别,它在pH4.5-7.0和高达45°C的范围内稳定。PbBgal35A从乳糖以32%(w/w)的转化率有效地合成了低聚半乳糖,并从乳果糖以21.9%(w/w)的转化率有效地合成了果糖基低聚半乳糖。此外，该酶催化鲜奶中低含量乳糖合成低聚半乳糖，当反应在45和4°C下进行时，获得了17.1%(w/w)和7.8%(w/w)的GOS转化率，分别。这些特性使PbBgal35A成为商业上用于制造富含GOS的乳制品的理想候选物。
