Purification and properties of β-xylosidase from Penicillium wortmanni

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Abstract
A purification method for an extracellular .beta.-xylosidase (.beta.-D-xyloside xylohydrolase, EC 3.2.1.37) induced in P. wortmanni is described. It includes diafiltration, acetone precipitation and hydroxylapatite chromatography. The enzyme has a MW of about 100,000. Its pH optimum is at pH 3.3-4.0 and it is most stable at pH 5.0-6.0. Its isoelectric point is at pH 5.0. Sulfhydryl and histidine reagents are not inhibitory. The influence of added cations and anions is negligible. N-Bromosuccinimide oxidation of 2-3 tryptophan residues per molecule entails rapid inactivation. Glycon-specificity studies indicate strict requirements at C-2, C-3, C-4 and C-5, although .alpha.-L-arabinopyranosides are substrates. As the enzyme seems to hydrolyse xylooligosaccharides endwise, with retention of configuration in the reaction product, the enzyme is a true glycosidase, probably operating by a double-inversion mechanism.