Purification and characterization of an extracellular β-glucosidase from the anaerobic fungus Piromyces sp. strain E2

An extracellular β-glucosidase (EC 3.2.2.21) from the anaerobic fungus Piromyces sp. strain E2 was purified. The enzyme is a monomer with a molecular mass of 45 kDa and a pI of 4.15. The enzyme readily hydrolyzes p-nitrophenyl-β-d-glycoside, p-nitrophenyl-β-d-fucoside, cellobiose, cellotriose, cellotetraose and cellopentaose but is not active towards Avicel, carboxymethylcellulose, xylan, p-nitrophenyl-β-d-galactoside and p-nitrophenyl-β-d-xyloside. To cleave p-nitrophenyl-β-d-glucoside the maximum activity is reached at pH 6.0 and 55°C, and the enzyme is stable up to 72 h at 40°C. Activity is inhibited by d-glucurono-δ-lactone, cellobiose, sodium dodecyl sulfate, Hg2+ and Cu2+ cations. With p-nitrophenyl-β-d-glycoside, p-nitrophenyl-β-d-fucoside, and. cellobiose as enzyme substrates, the Km and Vmax balues are 1.5 mM and 25.5 IU·mg-1, 1.1. mM and 133 IU·mg-1, and 0.05 mM and 55.6 IU·mg-1, respectively.