title: Beta-Xylosidases and a nonspecific wall-bound beta-glucosidase of the yeast Cryptococcus albidus.
abstract: Cryptococcus albidus grown on wood xylans possesses a soluble intracellular beta-xylosidase (EC 3.2.1.37) as an additional constituent of the xylan-degrading enzyme system of this yeast. The enzyme attacks linear 1,4-beta-xylooligosaccharides in an exo-fashion, liberating xylose from the non-reducing ends. The activity of the enzyme increases in the cells during growth on xylan and incubation with xylobiose or methyl beta-D-xylopyranoside which are the best inducers of extracellular beta-xylanase (EC 3.2.1.8). Various alkyl-,alkyl-1-thio- and aryl beta-D-xylopyranosides were excellent inducers of a different beta-xylosidase of Cryptococcus albidus. This enzyme is localized outside the plasma membrane and is principally associated with cell walls. Unlike the soluble intracellular beta-xylosidase, the wall-bound enzyme does not hydrolyze xylooligosaccharides. Evidence has been obtained that beta-xylosidase activity in the cell walls is not due to the presence of a specific aryl beta-xylosidase, but is exhibited by a nonspecific beta-glucosidase (EC 3.2.1.21) inducible by beta-D-xylopyranosides. The ratio of beta-glucosidase and beta-xylosidase activity in the cells and isolated cell walls from yeast induced by various beta-xylopyranosides and beta-glucopyranosides was very similar. Both wall-bound activities were inhibited in a similar pattern by inhibitors of beta-glucosidases, 1,5-gluconolactone and nojirimycin. This bifunctional enzyme does not bear any relationship to the utilization of xylans in Cryptococcus albidus.
mesh_terms: D002473:Cell Wall / Q000201:enzymology*; D003454:Cryptococcus / Q000201:enzymology*; D004790:Enzyme Induction; D005959:Glucosidases / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D007700:Kinetics; D013379:Substrate Specificity; D014995:Xylosidases / Q000302:isolation & purification / Q000378:metabolism*; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D005959:Glucosidases; D006026:Glycoside Hydrolases; D014995:Xylosidases; D001617:beta-Glucosidase; C026579:exo-1,4-beta-D-xylosidase