Purification and regulation of the synthesis of a β-xylosidase fromAspergillus nidulans

(EC 3.2.1.37) has been purified from Aspergillus nidulans mycelium grown on oat-spelt xylan as sole carbon source. Its pH optimum for activity was found to be 5.0 and the optimum temperature was 50C. Its molecular mass was estimated by gel filtration to be 180000. Using p-nitrophenyl-P-D-xylopyranoside as substrate, the K, and V,,,,, values have been found to be 1 .l mM and 25.6 wrnol min-' (mg protein)-', respectivdy. Enzyme activity was inhibited by Hg'+, Ag2+, and CL?+ at a concentration of 1 X lop3 M. The synthesis of /3-xylosidase in A. nidulans is strongly induced by arabinose and xylose and is subject to carbon catabolite repression mediated by the creA gene product.