Purification and characterization of an extracellular -glucosidase from the thermophilic fungus Sporotrichum thermophile and its influence on cellulase activity

Multiple forms of β-glucosidase (EC 3.2.1.21) of Sporotrichum thermophile were produced when the fungus was grown in a cellulose medium. One β-glucosidase was purified 16fold from 6-d-old culture filtrates by ion-exchange and gel-filtration chromatography. The purified enzyme was free of cellulase activity. It hydrolysed aryl β-d-glucosides and β-d-linked diglucosides. It was optimally active at pH 5·4, at 65 °C. The apparent K m values for p-nitrophenyl β-d-glucoside (PNPG) and cellobiose were 0·29 and 0·83 mm, respectively. Glucose, fucose, nojirimycin and gluconolactone inhibited β-glucosidase competitively. At high (> 1 mm) substrate concentration, β-glucosidase catalysed a parallel transglycosylation reaction. The transglycosylation product formed from cellobiose appeared to be a β-linked tetramer of glucose. Admixtures of β-glucosidase and cellulase components showed that the concept of cellobiose inhibition of cellulases was not valid for all components of the cellulase system of S. thermophile. β-Glucosidase supplementation also stimulated cellulose hydrolysis by cellulases when there was no accumulation of cellobiose in reaction mixture.