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Utilization of xylitol dehydrogenase in a combined microbial/enzymatic process for production of xylitol from D-glucose

机译:木糖醇脱氢酶在微生物/酶结合工艺中从D-葡萄糖生产木糖醇的应用

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The production of xylitol from D-glucose occurs through a three-step process in which D-arabitol and D-xylulose are formed as the first and second intermediate product, respectively, and both are obtained via microbial bioconversion reactions. Catalytic hydrogenation of D-xylulose yields xylitol; however, it is contaminated with D-arabitol. The aim of this study was to increase the stereoselectivity of the D-xylulose reduction step by using enzymatic catalysis. Recombinant xylitol dehydrogenase from the yeast Galactocandida mastotermitis was employed to catalyze xylitol formation from D-xylulose in an NADH-dependent reaction, and coenzyme regeneration was achieved by means of formate dehydrogenase-catalyzed oxidation of formate into carbon dioxide. The xylitol yield from D-xylulose was close to 100%. Optimal productivity was found for initial coenzyme concentrations of between 0.5 and 0.75 mM. In the presence of 0.30 M (45 g/L) D-xylulose and 2000 U/L of both dehydrogenases, exhaustive substrate turnover was achieved typically in a 4-h reaction time. The enzymes were recovered after the reaction in yields of approx 90% by means of ultrafiltration and could be reused for up to six cycles of D-xylulose reduction. The advantages of incorporating the enzyme-catalyzed step in a process for producing xylitol from D-glucose are discussed, and strategies for downstream processing are proposed by which the observed coenzyme turnover number of approx 600 could be increased significantly. [References: 21]
机译:由D-葡萄糖产生木糖醇是通过三步过程进行的,其中D-阿拉伯糖醇和D-木酮糖分别形成为第一和第二中间产物,并且两者均通过微生物生物转化反应获得。 D-木酮糖的催化加氢产生木糖醇。但是,它被D-阿拉伯糖醇污染了。这项研究的目的是通过使用酶催化来增加D-木酮糖还原步骤的立体选择性。酵母半乳杆菌乳腺炎的重组木糖醇脱氢酶用于催化NADH依赖性反应中D-木酮糖形成木糖醇的过程,并通过甲酸脱氢酶催化将甲酸氧化成二氧化碳来实现辅酶的再生。 D-木酮糖的木糖醇产率接近100%。发现初始辅酶浓度在0.5至0.75 mM之间时,生产率最佳。在存在0.30 M(45 g / L)D-木酮糖和2000 U / L两种脱氢酶的情况下,通常在4小时的反应时间内即可达到详尽的底物周转率。反应后通过超滤回收酶,收率约90%,可重复使用多达六个D-木酮糖还原循环。讨论了将酶催化步骤整合到由D-葡萄糖生产木糖醇的过程中的优势,并提出了下游加工策略,通过该策略可以显着增加约600的观察到的辅酶转换数。 [参考:21]

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