Coenzyme-dependent enzymatic synthesis of fine chemicals. Enzymatic synthesis of L-sorbose from D-glucose/D-fructose by intrasequential coenzyme regeneration

At present, L-sorbose is produced by catalytic hydration of D-glucose to sorbitol followed by fermentation to L-sorbose using Gluconobacter suboxydans or Acetobacter xylinum. Within this procedure problems arise with regard to nickel contamination of the applied microorganisms. Chemical oxidation of sorbitol suffers from lack of stereospecifity. Therefore, an extensive screening program was carried out to select microorganisms producing aldose reductase (ALR) and sorbitol-(SDH) or polyoldehydrogenases (PDH), respectively. To minimize co-factor consumption, the chosen pair of enzymes should should allow cofactor regeneration intrasequentially. Crude extracts from Gluconobacter oxydans, G. suboxydans, and G. melanogenes, which are already known from the industrial fermentation process gave the best results. Most encouraging results were obtained with Pichia strains. Both of their sorbitol transforming enzymes are presently purified and characterized.