Purification and Properties of an α-D-Xylosidase from Aspergillus niger

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Abstract
Two components of α-D-xylosidase (α-D-xylosidase I and II) were detected in the culture filtrate of Aspergillus nigher grown in a medium containing Sanzyme 1000-treated Glyloid 2A. The major component (α-D-xylosidase I) was purified to an electrophoretically pure state. The purified enzyme showed approximately 540-fold increase in specific activity over the original culture filtrate. The purified enzyme was shown to be an oligomeric protein consisting of four subunits, each of which had a molecular weight of 123,000. The enzyme showed the highest activity at pH 2.5–3.0 and 45°C, and was stable in the pH range from 3.0 to 7.0 and at the temperatures up to 60°C. The isoelectric point of this enzyme was pH 5.6. The purified enzyme was highly specific for p-nitrophenyl α-D-xylopyranoside and isoprimeverose (6-O-α-D-xylopyranosyl-D-glucopyranose). The apparent Km and Vmax values of the enzyme for p-nitrophenyl α-D-xylopyranoside and isoprimeverose were 10.5 mM and 40.8 μmol/min/mg protein, and 2.2 mM and 30 μmol/min/mg protein, respectively. The purified enzyme could also split off the α-D-xylopyranosyl residue on the non-reducing terminal of the backbone of oligo-xyloglucans such as α-D-xylopyranosyl-(1 ↑ 6)-β-D-glucopyranosyl-(1 ↑ 4) -{[α-D-xylopyranosyl- (1 ↑ 6)-]-β-D-glucopyranosyl-(1 ↑ 4)-2 -D-glucopyranose.