Liao W X, Earnest L, Kok S L, Jeyaseelan K
Department of Biochemistry, Faculty of Medicine, National University of Singapore.
Biochem Mol Biol Int. 1995 Jun;36(2):401-10.
The gene (xylA) encoding a thermostable xylose isomerase has been isolated and characterized from a thermophilic Bacillus species for the first time. The xylA open reading frame of 1323 bp encoded a protein containing 441 amino acids with a calculated molecular weight of 50,176. The amino acid sequence of this protein showed 76% homology to xylose isomerase isolated from Bacillus subtilis and contained all the important catalytic domains of the enzyme. The gene complemented the xyl-5 mutation and produced a functional enzyme constitutively in Escherichia coli. The crude cell-free extract of E. coli recombinants exhibited xylose isomerase activity over a wide range of temperatures from 60 to 100 degrees C with an optimal enzyme activity of 10.4 Units/mg protein at 85 degrees C. This optimal temperature was one of the highest reported so far for thermostable xylose isomerases. The recombinant enzyme was found to be a tetramer with each subunit having molecular weight of 50,000.
首次从嗜热芽孢杆菌属中分离并鉴定了编码热稳定木糖异构酶的基因（xylA）。1323 bp的xylA开放阅读框编码一种含有441个氨基酸的蛋白质，计算分子量为50,176。该蛋白质的氨基酸序列与从枯草芽孢杆菌中分离的木糖异构酶具有76%的同源性，并包含该酶的所有重要催化结构域。该基因弥补了xyl-5突变，并在大肠杆菌中组成型产生功能性酶。大肠杆菌重组体的粗无细胞提取物在60至100摄氏度的宽温度范围内表现出木糖异构酶活性，在85摄氏度时最佳酶活性为10.4单位/毫克蛋白质。这个最佳温度是迄今为止报道的热稳定木糖异构酶中最高的之一。发现重组酶是一种四聚体，每个亚基的分子量为50,000。
