Chang B S, Mahoney R R
Department of Food Science and Nutrition, University of Massachusetts, Amherst 01003.
J Dairy Res. 1989 Feb;56(1):117-27. doi: 10.1017/s0022029900026285.
beta-Galactosidase from an autolytic strain of Streptococcus salivarius subsp. thermophilus was purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 592 o-nitrophenyl beta-D-galactopyranoside U/mg at 37 degrees C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116,000. Enzyme stability was 37-83 times greater in milk than in buffer in the range 60-65 degrees C. At 60 degrees C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was approximately 0.5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35.1 kJ/mol.
来自嗜热唾液链球菌自溶菌株的β-半乳糖苷酶被纯化了109倍，达到近乎纯的状态。纯化酶的产率为41%，在37℃时比活性为592对硝基苯基β-D-吡喃半乳糖苷单位/毫克。存在两种同工酶，但仅检测到一个亚基，其分子量为116,000。在60 - 65℃范围内，酶在牛奶中的稳定性比在缓冲液中高37 - 83倍。在60℃时，在牛奶中的半衰期为146分钟。在缓冲液中的变性是一级反应，但在牛奶中，相对于酶浓度的总反应级数约为0.5。在牛奶中变性的活化能为453 kJ/mol，在缓冲液中为372 kJ/mol。在牛奶中乳糖水解的活化能为35.1 kJ/mol。
