The filamentous fungus Aspergillus versicolor produced large amounts of mycelial beta-xylosidase activity when grown on xylan or xylose as the only carbon source. The presence of glucose drastically decreased the level of beta-xylosidase activity, while cycloheximide prevented the induction of the enzymes by xylan or xylose. The beta-xylosidases induced by xylose or xylan were purified by a simple protocol involving DEAE-cellulose chromatography and ammonium sulphate precipitation. The purified enzymes were acidic proteins, with carbohydrate contents of 21% for that induced by xylose, and 47% for that induced by xylan. Their apparent molecular masses, estimated by gel filtration, and optimal temperatures for beta-xylosidase activities, were about 60 and 100 kDa, and 40 and 45 degreesC, respectively, for the enzymes induced by xylose and xylan. Xylose-induced beta-xylosidase exhibited an optimum pH of 6.0, while that of the xylan-induced enzyme was 5.5. Both purified beta-xylosidases exhibited also beta-galactosidase, beta-glucosidase and alpha-arabinosidase activities. In addition to synthetic substrates, the enzymes hydrolysed xylobiose and xylotriose, suggesting a physiological role. K-M values for p-nitrophenyl beta-D-xylopyranoside were 0.32 mM, for the xylose-induced beta-xylosidase, and 0.19 mM for the xylan-induced one. Xylose competitively inhibited both beta-xylosidases, with K-I values of 5.3 and 2.0 mM, for the enzymes induced by xylose or xylan, respectively. (C) 2003 Elsevier Ltd. All rights reserved.