Reversible inactivation of d-xylose utilization by d-glucose in the pentose-fermenting yeast Pachysolen tannophilus

Abstract A major problem in fermenting pentoses using lignocellulosic substrates is the presence of d -glucose which inhibits d -xylose utilization. We previously showed that d -glucose represses the induction of xylose reductase and xylitol dehydrogenase activities, thereby inhibiting d -xylose utilization in Pachysolen tannophilus . The question arose whether d -glucose can also inactivate d -xylose fermentation. P. tannophilus cells were grown on a defined d -xylose-containing liquid medium. At about 40 h, d -glucose was added to a final concentration of 3% (w/v). This led to a rapid cessation of d -xylose utilization, which resumed after 10–12 h before d -glucose was completely consumed. This suggests that d -glucose inactivated existing d -xylose catabolic enzymes and that inactivation was reversed at low d -glucose concentrations. This reversible inactivation was distinct from d -glucose repression. Addition of cycloheximide did not block the resumption of d -xylose consumption, suggesting that reactivation was independent of protein synthesis.