Purification and characterization of an extracellular β-glucosidase from the wood-grown fungus Xylaria regalis

Xylaria regalis, a wood-grown ascomycete isolated in Taiwan, produces β-glucosidase (EC 3.2.1.21) extracellularly. The β-glucosidase was purified to homogeneity by ammonium sulfate precipitation, ion-exchange, and gel filtration chromatography. The molecular mass of the purified enzyme was estimated to be 85 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With p-nitrophenyl β-D-glucopyranoside (PNPG) as the substrate at pH 5.0 and 50°C, the K(m) was 1.72 mM and V(max) was 326 μmol/min/mg. Optimal activity with PNPG as the substrate was at pH 5.0 and 50°C. The enzyme was stable at pH 5.0 at temperatures up to 50°C. The purified β-glucosidase was active against PNPG, cellobiose, sophorose, and gentiobiose, but did not hydrolyze lactose, sucrose, Avicel, and o- nitrophenyl β-D-galactopyranoside. The activity of β-glucosidase was stimulated by Ca²⁺, Mg²⁺, Mn²⁺, Cd²⁺ and β-mercaptoethanol, and inhibited by Ag²⁺, Hg²⁺, SDS, and p-chloromercuribenzoate (PCMB).