Abstract
This study reports the regulation and purification of b-glucosidases from a thermotolerant Aspergillus terreus AN1 strain, previously reported for efficient deinking of composite paper waste. The differential expression of four beta-glucosidase isoforms, in response to carbon sources in production medium, was studied by electrophoretically resolving proteins by polyacrylamide gel electro-phoresis analysis (PAGE) and developing zymograms using methylum-belliferyl b-D glucoside as substrate. Three b-glucosidases (bGI, bGII & bGIII) were purified using chromatographic techniques. SDS-PAGE revealed the respective molecular masses of bGI, bGII, and bGIII, as 29, 43, and 98 KDa, and isoelectric point (pI) to be 2.8, 3.7, and 3.0. The b-glucosidases exhibited diverse pH and temperature optima as well as stability. b-Glucosidase I (bGI) specifically recognized pNP-b-glucopyranoside (pNPG) as a substrate, whereas, b-glucosidase II (bGII) and III (bGIII) also showed activities against cellobiose and salicin. In contrast to bGII and bGIII, the activity of bGI was positively influenced in the presence of hexoses/pentoses and alcohols. Km and Vmax for hydrolysis of pNPG by bGI, bGII, andbGIII were found to be 14.2 mM and 166.9 µmol -1mg protein -1, 4.37 mM, and 34.7 µmol -1mg proteins -1, and 11.1 mM and 378.7µ mol -1 mg protein -1, respectively.Download PDF