Catabolite Repression of induction of aldose reductase activity and utilization of mixed hemicellulosic surgars in Candida guilliermondii

Abstract

NADPH-dependent aldose reductase activity induced by D-xylose or L-arabinose was detected in cell-free extracts of Candida guilliermondii, but only negligible activities were observed if D-glucose served as carbon source. The induction of aldose reductase activity on mixed sugars was investigated under resting cell conditions. D-Glucose repressed enzyme induction by D-xylose or L-arabinose to varying degrees, and L-arabinose 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 consumption 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 present in a mixture, the consumption of both pentoses was reduced by the presence of the second sugar, although both sugars were consumed simultaneously by cells. The results show that induction of aldose reductase activity and D-xylose utilization by cells of Candida guilliermondii are under control of glucose repression.

Metabolic behavior of immobilized Candida guilliermondii cells during batch xylitol production from sugarcane bagasse acid hydrolyzate

“…Xylose fermentation to ethanol was practically non-existent at the start of the run, due to at least four dierent causes: (a) presence of a more easily fermentable carbon source (glucose); (b) catabolite repression of the induction of XR activity (Sugai and Delgenes, 1995); (c) inactivation of the xylose transport system (Nobre et al, 1999); and (d) presence of oxygen favoring growth and respiration. The ethanol production was suppressed also at the end of the run, when the main fermentable substrates were nearly exhausted.…”

“…One of the proposed methods for minimizing the toxicity of such hydrolyzates is the use of high cell concentrations (Parajo et al, 1996), which can be ensured by cell immobilization within Ca-alginate beads (Carvalho et al, 2000). An unsolved problem is the presence of other sugars, such as glucose, which can inactivate the xylose transport system (Nobre et al, 1999) or repress the induction of XR activity (Sugai and Delgenes, 1995). Therefore, additional information on pentose-fermenting yeasts metabolism is necessary.…”

The behavior of key enzymes of xylose metabolism on the xylitol production by Candida guilliermondii grown in hemicellulosic hydrolysate

“…In fact, due to the mixture of sugars obtained in the hemicellulosic hydrolysate, the enhancement on xylose concentration promotes an increase in glucose available in fermentation medium. The presence of intracellular glucose may reduce the diVerential rate of XR synthesis induced by xylose, a phenomenon called partial or weaker carbon catabolite repression according to Sugai and Delgenes [22]. Furthermore, in the latter eVect, glucose does not disable the entry of xylose, but it may compete for the transport system in Candida guilliermondii, as noticed in Pichia stipitis and Candida shehatae.…”

Improvement of biotechnological xylitol production by glucose during cultive of Candida guilliermondii in sugarcane bagasse hydrolysate

“…Rosa et al (1998) observed an improvement of xylitol formation by C. guilliermondii in synthetic medium containing xylose (60 g l -1 ) and glucose (5 g l -1 ) and according to Felipe et al (1993), this improvement depended on glucose:xylose ratio. Sugai and Delgenes (1995) reported that the glucose partially repressed the induction of aldose reductase of C. guilliermondii by xylose, and the intensity of the catabolite repression was correlated to the glucose concentration in the induction system. The stimulation of xylose metabolism by glucose can be explained by the generation of intermediary metabolites for the initial steps of xylose metabolism and the pentose phosphate pathway through glucose metabolism, since coenzymes such as NADH and NADPH are essential for the enzymatic reduction of xylose with xylose reductase (Meinander et al 1999;Chung et al 2002).…”