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

l-Xylulose was used as a raw material for the production of l-xylose with a recombinantly produced Escherichia colil-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 Km of 41 mM and a Vmax of 0.23 μmol/(mg min). The half-lives determined for the enzyme at 35 °C and at 45 °C were 6 h 50 min and 1 h 31 min, 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%.

► l-Fucose isomerase catalyzed isomerization of l-xylulose to l-xylose does not produce l-lyxose. ► New characteristics on the catalytic mechanisms related to l-fucose isomerase are presented. ► A potential pathway for the production of the pharmaceutically important intermediate l-xylose is presented.