Induction of aldose reductase and xylitol dehydrogenase activities in Candida tenuis CBS 4435

Abstract

In this study the ability of various sugars and sugar alcohols to induce aldose reductase (xylose reductase) and xylitol dehydrogenase (xylulose reductase) activities in the yeast Candida tenuis was investigated. Both enzyme activities were induced when the organism was grown on D-xylose or L-arabinose as well as on the structurally related sugars D-arabinose or D-lyxose. Mixtures of D-xylose with the more rapidly metabolizable sugar D-glucose resulted in a decrease in the levels of both enzymes formed. These results show that the utilization of D-xylose by C. tenuis is regulated by induction and catabolite repression. Furthermore, the different patterns of induction on distinct sugars suggest that the synthesis of both enzymes is not under coordinate control.

Xylose reductase activity in Debaryomyces hansenii UFV-170 cultivated in semi-synthetic medium and cotton husk hemicellulose hydrolyzate

“…It is likely that the yeast growth on D-xylose or xylitol was limited by the transport of these carbon sources across the cell membrane, or by their successive conversion to xylulose-5-phosphate, thus reaching cell concentrations comparable to that on glucose (9.48 ± 0.11 g DW l -1 ). Similarly, Candida tenuis CBS 4435 showed the highest biomass production on hexoses, whereas the growth on xylose became very effective after 24 h of cultivation [8], thus proving the effectiveness of xylose metabolism in this yeast. Figure 1b shows the effect of the different carbon sources on the specific growth rate (l) of D. hansenii UFV-170.…”

“…Several works showed that the expression of the XR gene is subject to regulation by induction and catabolite repression [8,[16][17][18][19]. D-Xylose is reported to be the best XR gene inducer, followed closely by L-arabinose [8,[18][19][20], which suggests that in general pentoses can be effective in the induction of XR gene.…”

“…Several works showed that the expression of the XR gene is subject to regulation by induction and catabolite repression [8,[16][17][18][19]. D-Xylose is reported to be the best XR gene inducer, followed closely by L-arabinose [8,[18][19][20], which suggests that in general pentoses can be effective in the induction of XR gene. Negligible activity has been detected with cellobiose, D-mannose, D-glucose, D-galactose, D-fructose and glycerol as substrates [8,19], thus suggesting that the XR gene expression is partially or practically suppressed (catabolite repression) on media containing these substrates [19][20][21].…”

“…Yeasts and moulds are capable of converting xylose to xylitol by the action of xylose reductase (XR, EC 1.1.1.21), which catalyzes the first step in D-xylose assimilation, i.e., a NADPH-dependent or, in some cases, NADH-dependent reduction of D-xylose to xylitol [6][7][8]. Nevertheless, the conversion process using microorganisms can lead to unsatisfactory productions of xylitol due to the influence of some culture conditions.…”

Seleção de leveduras para bioconversão de D-xilose em xilitol

“…As hemiceluloses podem ser classificadas como xilanas, mananas, arabinoxilanas, arabinogalactanas e arabinanas BIELY, 1985;KERN et al, 1997;AGUIAR et al, 1999). A xilana é hidrolisada em açúcares monômeros constituintes (glicose, xilose, arabinose, galactose, manose e outros oligossacarídeos) usando ácido diluído, álcali, explosão a vapor, explosão com amônio (AFEX) (HOLTZAPPLE et al, 1991) ou uma mistura de tratamentos enzimaticos (amilase, xilanase e celulase) (HESPELL et al, 1997, SAHA et al).…”