Simultaneous synthesis of sorbitol and gluconic acid by glucose-fructose-oxidoreductase

Gluconolactone and sorbitol are simultaneously synthesized from glucose-fructose-mixtures obtained from starch or saccharose by a glucose-fructose-exidoreductase (GFOR). Gluconolactone is immediately hydrolysed to gluconic acid by gluconolactonase (GL). As a result of the screening of microorganisms, good GFOR and GL activities were found in Zymomonas mobilis. Some other bacteria and yeasts contain only GL activity. GFOR contains firmly bound NADP(H) and does not require any added cofactor for activity. The synthesis of GFOR from Zymomonas mobilis was induced by 20% glucose medium. Purification of this enzyme was 98-fold with a 49% recovery and a specific activity of 206 U/mg. According to SDS gel electrophoresis it has a subunit size of 40 000 daltons and can be stabilized by glycerol.