Inducible β-Xyloside Permease as a Constituent of the Xylan-Degrading Enzyme System of the Yeast Cryptococcus Albidus
The yeast, Crytococcus albidus, depending on whether it is grown on xylan or glucose, differs remarkably in the ability to take up inducers of extracellular endo-1,4-β-xylanase synthesis. In washed, glucose-grown cells the initially low ability to take up xylobiose or methyl β-D-xylopyranoside, increases during incubation with these compounds after a lag-phase shorter than the induction time of the extracellular β-xylanase. Using of methyl β-D-[U-14C] xylopyranoside as a very slowly metabolizable inducer of xylobiose or methyl xyloside uptake is due to induction of an active transport system for methyl β-D-xyloside and β-1,4,-xylooligosaccharides. The system is called β-xyloside permease. The permease activity of induced cells decreases in the absence of β-xylanase inducers. The induction of permease as well as its inactivation (degradation) can be prevented with cycloheximide, thus both events appear to be dependent on de novo protein synthesis. In analogy with other active transport systems, β-xyloside permease function can be effectively blocked by inhibitors of energy metabolism in the cells.