Novel Enzymatic Method for the Production of Xylitol fromD-Arabitol byGluconobacter oxydans

Cloning of the Xylitol Dehydrogenase Gene fromGluconobacter oxydansand Improved Production of Xylitol fromD-Arabitol

“…The xylitol-producing reaction was done at pH 6.0 over 48 h, sparging the air at a ‰ow rate of 0.75 vvm, with the temperature at 339 C and an agitation rate of 400 rpm. Since we observed in the previous report that the addition of ethanol to the reaction mixture increased xylitol productivity by the resting cell reaction with G. oxydans, 13) xylitol productivity in the presence of ethanol was also examined. The initial agitation rate was 600 rpm and the oxidation of D-arabitol to D-xylulose was allowed to proceed for 9 h, after which 9 ml ethanol was added to the reaction mixture and the agitation rate was reset to 400 rpm.…”

“…13) When the reaction mixture was prepared with 10z (w W v) of intact G. oxydans cells as a catalyst, 29.2 g W l xylitol was produced from 52.4 g W l D-arabitol in 27 h; however, when the cell content was reduced to 1z (w W v), only 9 g W l xylitol was produced from 100 g W l D-arabitol over 48 h, and some D-xylulose still remained in the reaction mixture. From a practical point of view, increasing the conversion rate of D-xylulose to xylitol would greatly improve the xylitol yield and reˆne the manufacturing process.…”

Transaldolase/Glucose-6-phosphate Isomerase Bifunctional Enzyme and Ribulokinase as Factors to Increase Xylitol Production fromD-Arabitol inGluconobacter oxydans

“…Our previous stu dies suggested that enhancement of NADH supply was essential for increasing the yield of xylitol from Darabitol in G. oxydans, 8,10) but the NADH genera tion mechanism of G. oxydans remained unclear.…”

“…G. oxydans has a membranebound AraDH and irrever sibly converts Darabitol to Dxylulose. 8,9) Neverthe less, some Dxylulose still remained in the reaction mixture, even using recombinant strains of G. oxyd ans that had 11fold higher XDH activity than the wildtype strain. 10) From a practical point of view, increasing the conversion rate of Dxylulose to xylitol would improve the yield of xylitol and rene the manufacturing process.…”

“…It was suggested that the ethanol was oxidized by an NADdependent soluble alcohol dehydrogenase, resulting in the regeneration of NADH. 8,10) Since XDH is highly specic for NADH, it requires a sup ply of NADH for the ecient conversion of Dxylu lose to xylitol.…”