Biotechnol Prog. 2014 Jan-Feb;30(1):38-47. doi: 10.1002/btpr.1828.
Many β-galactosidases show large differences in galacto-oligosaccharide (GOS) production and lactose hydrolysis. In this study, a kinetic model is developed in which the effect of lactose, glucose, galactose, and oligosaccharides on the oNPG converting activity of various β-galactosidases is quantified. The use of oNPG as a competing substrate to lactose yields more information than can be obtained by examining only the conversion of lactose itself. The reaction rate with lactose or oligosaccharides as substrate relative to that with water as acceptor is much higher for the β-galactosidase of Bacillus circulans than the bgalactosidases of Aspergillus oryzae and Kluyveromyces lactis. In addition, the β-galactosidase of B.circulans has a high reaction rate with galactose as acceptor, in contrast to those of A. oryzae and K. lactis. The latter two are strongly inhibited by galactose. These differences explain why β-galactosidase of B. circulans gives higher yields in GOS production than other β-galactosidases. Many of the reaction rate constants for the β-galactosidase isoforms of B. circulans increase with increasing molecular weight of the isoform. This indicates that the largest isoform β-gal-A is most active in GOS production. However, its hydrolysis rate is also much higher than that of the other isoforms, which results in a faster hydrolysis of oligosaccharides as well.
许多β-半乳糖苷酶在半乳糖低聚糖（GOS）生产和乳糖水解方面表现出很大的差异。在本研究中，建立了一个动力学模型，其中定量了乳糖、葡萄糖、半乳糖和低聚糖对各种β-半乳糖苷酶的 oNPG 转化活性的影响。与仅检查乳糖本身的转化相比，使用 oNPG 作为竞争底物可以提供更多信息。以乳糖或低聚糖为底物与以水为受体的反应速率对于环状芽孢杆菌的β-半乳糖苷酶比米曲霉和乳酸克鲁维酵母的β-半乳糖苷酶高得多。此外，与米曲霉和乳酸克鲁维酵母的β-半乳糖苷酶相比，环状芽孢杆菌的β-半乳糖苷酶具有较高的以半乳糖为受体的反应速率。后两者受半乳糖强烈抑制。这些差异解释了为什么环状芽孢杆菌的β-半乳糖苷酶在 GOS 生产中比其他β-半乳糖苷酶产生更高的产量。随着同工酶分子量的增加，环状芽孢杆菌β-半乳糖苷酶同工型的许多反应速率常数增加。这表明最大的同工酶β-Gal-A 在 GOS 生产中最活跃。然而，它的水解速率也比其他同工型高得多，这导致低聚糖的水解更快。
