Ohtsu N, Motoshima H, Goto K, Tsukasaki F, Matsuzawa H
Research Center, Yotsuba Milk Products Co., Ltd., Hokkaido, Japan.
Biosci Biotechnol Biochem. 1998 Aug;62(8):1539-45. doi: 10.1271/bbb.62.1539.
We purified and characterized a thermophilic beta-galactosidase from Thermus sp. A4 isolated from the Atagawa hot spring (Shizuoka, Japan). The enzyme was monomeric, and its molecular mass was estimated to be 75 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme was extremely thermostable and retained its full activity after incubation at 70 degrees C for 20 h. The Km observed were 5.9 mM for ortho-nitrophenyl beta-D-galactopyranoside and 19 mM for lactose. We cloned and analyzed the complete sequence of the gene encoding this enzyme. It was found to consist of 645 amino acid residues. We propose that this enzyme and seven other unclassified beta-galactosidases are new members of family 42 of the glycosyl hydrolases.
我们从日本静冈县热川温泉分离出的嗜热栖热菌（Thermus sp.）A4中纯化并鉴定了一种嗜热β-半乳糖苷酶。该酶为单体，通过SDS-聚丙烯酰胺凝胶电泳估计其分子量为75 kDa。该酶具有极高的热稳定性，在70℃孵育20小时后仍保留其全部活性。观察到的对邻硝基苯基β-D-吡喃半乳糖苷的Km为5.9 mM，对乳糖的Km为19 mM。我们克隆并分析了编码该酶的基因的完整序列。发现它由645个氨基酸残基组成。我们认为该酶和其他七种未分类的β-半乳糖苷酶是糖基水解酶家族42的新成员。
