title: Utilization of xylitol dehydrogenase in a combined microbial/enzymatic process for production of xylitol from D-glucose.
abstract: 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.
authors.affiliation: Division of Biochemical Engineering, Institute of Food Technology, University of Agricultural Sciences Vienna, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Mayer
authors.forename: Klaus D
authors.initials: KD
authors.lastname: Kulbe
authors.forename: Bernd
authors.initials: B
authors.lastname: Nidetzky
mesh_terms: D001173:Arthrobacter / Q000201:enzymology; D050542:D-Xylulose Reductase; D020576:Gluconobacter / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007700:Kinetics; D008828:Microbiological Techniques / Q000379:methods; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000378:metabolism; D004718:Saccharomycetales / Q000378:metabolism; D013401:Sugar Alcohol Dehydrogenases / Q000378:metabolism*; D013402:Sugar Alcohols / Q000378:metabolism; D014993:Xylitol / Q000378:metabolism*; D014996:Xylulose / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D013402:Sugar Alcohols; D009243:NAD; D014996:Xylulose; D013401:Sugar Alcohol Dehydrogenases; D050542:D-Xylulose Reductase; D005947:Glucose; D014993:Xylitol; C014999:arabitol