Yoon Ran-Young, Yeom Soo-Jin, Kim Hye-Jung, Oh Deok-Kun
Department of Bioscience and Biotechnology, 1 Hwayang-dong, Gwangjin-gu, Konkuk University, Seoul 143-701, Republic of Korea.
J Biotechnol. 2009 Jan 1;139(1):26-32. doi: 10.1016/j.jbiotec.2008.09.012. Epub 2008 Oct 15.
A substrate specificity study of the recombinant D-ribose-5-phosphate isomerase (RpiB) from Clostridium thermocellum was performed. Among all aldopentoses and aldohexoses, the RpiB enzyme displayed activity with L-talose, D-ribose, D-allose, L-allose, L-ribose, and D-talose in decreasing order. The products released were L-tagatose, D-ribulose, D-psicose, L-psicose, L-ribulose, and D-tagatose, respectively. The enzyme showed specificity for aldose substrates possessing hydroxyl groups oriented in the same direction at the C2, C3, and C4 positions. Molecular modeling of the enzyme suggests that the novel substrate specificity may be explained by substrate interactions with residues Tyr42, His98, and His9, which interact with the hydroxyl groups of C2, C3, and C4, respectively, oriented in the same direction. L-Talose and D-ribulose exhibited the highest activity among the aldoses and ketoses, respectively. Ribose 5-phosphate isomerase catalyzed the conversion of L-talose to L-tagatose with an 89% conversion yield after approximately 90 min, while D-ribulose was converted to D-ribose with a 38% conversion yield.
对来自嗜热栖热梭菌的重组D-核糖-5-磷酸异构酶（RpiB）进行了底物特异性研究。在所有戊醛糖和己醛糖中，RpiB酶对L-塔罗糖、D-核糖、D-阿洛糖、L-阿洛糖、L-核糖和D-塔罗糖表现出活性，活性依次降低。释放的产物分别是L-塔格糖、D-核酮糖、D-阿洛酮糖、L-阿洛酮糖、L-核酮糖和D-塔格糖。该酶对在C2、C3和C4位置具有同向羟基的醛糖底物具有特异性。该酶的分子模型表明，新的底物特异性可能是由底物与Tyr42、His98和His9残基的相互作用所解释，这些残基分别与同向的C2、C3和C4羟基相互作用。L-塔罗糖和D-核酮糖在醛糖和酮糖中分别表现出最高活性。核糖5-磷酸异构酶在约90分钟后催化L-塔罗糖转化为L-塔格糖，转化率为89%，而D-核酮糖转化为D-核糖的转化率为38%。
