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 Ag⁺, Hg²⁺, SDS, and p-chloromercuribenzoate (PCMB). Received: 30 March 1996 / Accepted: 3 May 1996     

Physical mapping of the mitochondrial DNA from Aspergillus niger

Abstract The mitochondrial DNA was isolated from Aspergillus niger WU-2223L, a citric acid-production strain, and characterized by restriction-endonuclease mapping. Cloned fragments which covered the total range of the mitochondrial DNA were assembled and utilized to construct the restriction-endonuclease map for nine restriction enzymes. This map showed that the mitochondrial DNA was a circular molecule of 32.6 kb.