Production of l-xylose from l-xylulose using Escherichia coli l-fucose isomerase

l-Xylulose was used as a raw material for the production of l-xylose with a recombinantly produced Escherichia coli l-fucose isomerase as the catalyst. The enzyme had a very alkaline pH optimum (over 10.5) and displayed Michaelis-Menten kinetics for l-xylulose with a K _m of 41mM and a V _max of 0.23μmol/(mgmin). The half-lives determined for the enzyme at 35°C and at 45°C were 6h 50min and 1h 31min, respectively. The reaction equilibrium between l-xylulose and l-xylose was 15:85 at 35°C and thus favored the formation of l-xylose. Contrary to the l-rhamnose isomerase catalyzed reaction described previously [14] l-lyxose was not detected in the reaction mixture with l-fucose isomerase. Although xylitol acted as an inhibitor of the reaction, even at a high ratio of xylitol to l-xylulose the inhibition did not reach 50%.