Life Science College, Yuncheng University, Yuncheng 044000, China.
Folia Microbiol (Praha). 2012 Sep;57(5):447-53. doi: 10.1007/s12223-012-0160-3. Epub 2012 May 13.
A halophilic isolate Thalassobacillus sp. LY18 producing extracellular amylase was isolated from the saline soil of Yuncheng Salt Lake, China. Production of the enzyme was synchronized with bacterial growth and reached a maximum level during the early stationary phase. The amylase was purified to homogeneity with a molecular mass of 31 kDa. Major products of soluble starch hydrolysis were maltose and maltotriose, indicating an α-amylase activity. Optimal enzyme activity was found to be at 70°C, pH 9.0, and 10 % NaCl. The α-amylase was highly stable over broad temperature (30-90°C), pH (6.0-12.0), and NaCl concentration (0-20 %) ranges, showing excellent thermostable, alkalistable, and halotolerant nature. The enzyme was stimulated by Ca(2+), but greatly inhibited by EDTA, indicating it was a metalloenzyme. Complete inhibition by diethyl pyrocarbonate and β-mercaptoethanol revealed that histidine residue and disulfide bond were essential for enzyme catalysis. The surfactants tested had no significant effects on the amylase activity. Furthermore, it showed high activity and stability in the presence of water-insoluble organic solvents with log P (ow) ≥ 2.13.
从中国运城盐湖的盐土中分离到一株产胞外淀粉酶的嗜盐菌，命名为 Thalassobacillus sp. LY18。该酶的合成与菌体生长同步，在静止期早期达到最大水平。淀粉酶经纯化后为 31 kDa 的单一条带，为同源蛋白，确定为胞外α-淀粉酶。该酶最适反应条件为 70℃、pH9.0、10%NaCl，具有较宽的温度（30-90℃）、pH（6.0-12.0）和 NaCl 浓度（0-20%）范围，表现出良好的热稳定性、碱性稳定性和耐盐性。该酶对 Ca2+有激活作用，对 EDTA 有强烈抑制作用，说明其为金属酶。二乙基焦碳酸酯和β-巯基乙醇的完全抑制表明组氨酸残基和二硫键对酶催化作用是必需的。测试的表面活性剂对酶活性没有显著影响。此外，它在 log P (ow)≥2.13 的疏水性有机溶剂中具有较高的活性和稳定性。
