嗜热脂肪芽孢杆菌耐热木糖异构酶的特性

CHARACTERISTICS OF XYLOSE ISOMERIZATION CATALYZED BY THERMOSTABLE XYLOSE ISOMERASE FROM B. STEAROTHERMOPHILUS

嗜热脂肪芽抱杆菌在木糖或木聚糖诱导下产生木糖异构酶。从破碎细胞中分离到该酶。经硫酸铵沉淀，热处理及SephadexG-200柱层析等步骤获得纯化了19倍的酶制备物。该酶反应的最适pH值为7.5，在pH6．2～8．0范围内稳定，最适反应温度为80℃，低于此温度时酶有很好稳定性。该酶对底物木糖的Km值为6．67mmol／L，Mg2+、Co2+和Mn2+对该酶有激活作用，而Zn2+、Cu2+和Fe2+对酶有抑制作用。酶制备物转化木糖为木酮糖产率为18％。

Xylose isomerase was produced by Bacillus stearothermophilus when the medium contained xylose or xylan. The enzyme was isolated from the cells and purified by ammonium sulphate precipitation, heat-treatment and chromatography on Sephadex G-200 column. The enzyme preparation catalyzed the conversion reaction of xylose to xylulose with the optimum PH 7.5 and the optimum temperature 80℃. Under conditions of PH 6.2～8.0 and temperature below 80℃, the enzyme was stable. The Km of the enzyme was 6.67 mM when xylose was used as the substrate. The enzyme was activated by Mg2+, Co2+ and Mn2+ and inhibited by Zn2+, Cu2+ and Fe3+.