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 41 mM and a V(max) of 0.23 μmol/(mg min). The half-lives determined for the enzyme at 35 °C and at 45 °C were 6h 50 min and 1h 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%.