Induction of Xylose Reductase and Xylitol Dehydrogenase Activities on Mixed Sugars in Candida guilliermondii

Abstract

The ability of various sugars to induce xylose reductase (aldose reductase, EC 1.1.1.21) and xylitol dehydrogenase (D-xylulose reductase, EC 1.1.1.9) activities in Candida guilliermondii was studied. D-Xylose was found to be the best inducer of activities of both enzymes, followed closely by L-arabinose. Very low xylose reductase activity was induced by cellobiose, D-mannose, D-glucose, D-galactose, D-fructose or glycerol. With xylitol dehydrogenase, cellobiose and D-fructose caused partial induction of enzyme activity, while negligible activity was induced by D-mannose, D-glucose, D-galactose or glycerol. Several sugars were tested for the ability to repress the induction by D-xylose of xylose reductase and xylitol dehydrogenase activities in C. guilliermondii. Enzyme activities induced on D-xylose served as controls. L-Arabinose, cellobiose and D-galactose did not repress enzyme induction by D-xylose, while D-mannose, D-glucose and D-fructose repressed enzyme induction to varying extents. Results from enzyme induction generally correlated with patterns of mixed sugar utilization, with some anomalies associated with the utilization of D-galactose and D-fructose in the presence of D-xylose. The results show that the utilization of D-xylose by C. guilliermondii is subject to regulation by induction and catabolite repression.