Characterization of β-xylosidase enzyme from a Pichia stipitis mutant

β-Xylosidase production was maximal for the mutant Pichia stipitis NP54376 grown on xylan as the sole carbon source. β-Xylosidase was purified from culture supernatant by (NH₄)₂SO₄ precipitation and a hydrophobic interaction chromatography on phenyl sepharose. Optima of pH and temperature were 5.0 and 50 °C, respectively. The enzyme was inhibited by 2-mercaptoethanol (100%) and Fe³⁺ (80%), and moderately affected by Cu²⁺, Ag⁺, NH₄⁺ and Mg²⁺ and SDS. The purified xylosidase hydrolyzed xylobiose and xylo-oligosaccharides and it did not exhibit activity against cellulose, starch, maltose and cellobiose. 2.5 g l^-1 glucose repressed β-xylosidase activity in the NP54376 strain. The K_m and V_max values on p-nitrophenyl-β-xylopyranoside were 1.6 mM and 186 μmol p-nitrophenyl min^-1 mg^-1 protein, respectively. Analysis of the hydrolysis products by HPLC indicated that the major hydrolysis product is xylobiose in all the carbon sources tested.