Simpson H D, Haufler U R, Daniel R M
Department Biological Sciences, University of Waikato, Hamilton, New Zealand.
Biochem J. 1991 Jul 15;277 ( Pt 2)(Pt 2):413-7. doi: 10.1042/bj2770413.
Endo-1,4-beta-xylanase (EC 3.2.1.8) was isolated from the culture supernatant of Thermotoga sp. strain FjSS3-B.1, an extremely thermophilic anaerobic eubacterium which grows optimally at 80 degrees C. Activity was purified 165-fold by anion-exchange and hydroxyapatite chromatography. The enzyme has an Mr of 31,000 as determined by SDS/PAGE and 35,000 by analytical gel filtration. The optima for activity and stability for purified xylanase were between pH 5.0 and 5.5. At pH 5.5, which is the optimum pH for thermostability, t1/2 (95 degrees C) is 90 min. The thermostability was improved by immobilization of the xylanase on to porous glass beads; t1/2 (105 degrees C) is 10 min. Several additives, such as sorbitol and xylan, were also found to increase the thermostability. At 130 degrees C, the half-life of immobilized xylanase in the presence of 90% sorbitol was 1.3 min. At 130 degrees C in molten sorbitol half of the enzyme denatured rapidly, but the remainder appeared to have a half-life of about 60 min.
内切-1,4-β-木聚糖酶（EC 3.2.1.8）是从嗜热栖热菌属菌株FjSS3-B.1的培养上清液中分离得到的，该菌株是一种极端嗜热厌氧真细菌，在80℃时生长最佳。通过阴离子交换和羟基磷灰石色谱法将活性纯化了165倍。经SDS/PAGE测定，该酶的相对分子质量为31000，经分析凝胶过滤测定为35000。纯化的木聚糖酶的活性和稳定性最佳pH值在5.0至5.5之间。在pH 5.5（热稳定性的最佳pH值）时，t1/2（95℃）为90分钟。通过将木聚糖酶固定在多孔玻璃珠上提高了热稳定性；t1/2（105℃）为10分钟。还发现几种添加剂，如山梨醇和木聚糖，可提高热稳定性。在130℃时，固定化木聚糖酶在90%山梨醇存在下的半衰期为1.3分钟。在130℃的熔融山梨醇中，一半的酶迅速变性，但其余部分的半衰期约为60分钟。
