Simultaneous enzymatic synthesis of gluconic acid and sorbitol: production, purification, and application of glucose-fructose oxidoreductase and gluconolactonase.

With regard to the enzymatic synthesis of sorbitol and gluconic acid, a screening was carried out to identify promising producers of glucose-fructose oxidoreductase (GFOR) and gluconolactonase (GL). Zymomonas mobilis DSM 473 and Rhodotorula rubra DSM 70403 have been selected for the synthesis of GFOR and GL, respectively. Maximal enzyme production by these organisms has been achieved at D-glucose concentrations of 200 and 150 g/L, respectively. Both GFOR and GL were purified and characterized with respect to some of their catalytic properties. GL showed strict specificity for 1,5-(delta)-lactones and was activated by Mg2+ and Mn2+ ions. The potential use of soluble GFOR is limited by its inactivation during substrate conversion, and the effects of reaction temperature and pH on the "catalytic" stability of GFOR were evaluated. Exogenous addition of auxiliary GL had no effect on oxidoreductase stability and did not improve productivities.