CATABOLITE REPRESSION OF INDUCTION OF ALDOSE REDUCTASE-ACTIVITY AND UTILIZATION OF MIXED HEMICELLULOSIC SUGARS IN CANDIDA-GUILLIERMONDII

NADPH-dependent aldose reductase activity induced by D-xylose or L-ara binose was detected in cell-free extracts of Candida guilliermondii, b ut only negligible activities were observed if D-glucose served as car bon source. The induction of aldose reductase activity on mixed sugars was investigated under resting cell conditions. D-Glucose repressed e nzyme induction by D-xylose or L-arabinose to varying degrees, and L-a rabinose inhibited enzyme induction by D-xylose. During incubation in a mixture of D-xylose-D-glucose, glucose consumption by cells was fast and simultaneous with D-xylose utilization. Repression of D-xylose co nsumption by D-glucose was dependent on hexose initial concentration. L-arabinose consumption was poor when it was present as the only sugar and in a mixture with D-glucose; this pentose depletion occurred only when all hexose was consumed. When D-xylose and L-arabinose were pres ent in a mixture, the consumption of both pentoses was reduced by the presence of the second sugar, although both sugars were consumed simul taneously by cells. The results show that induction of aldose reductas e activity and D-xylose utilization by cells of Candida guilliermondii are under control of glucose repression.