Xylose and ethanol stimulate a thermostable β-glucosidase from Humicola brevis var. thermoidea.

β-glucosidase from Humicola brevis var. thermoidea (BglHb) was purified and biochemically characterized. The enzyme was purified 418.1-fold with 4.2% yield; the apparent molecular mass, determined by SDS-PAGE was 125 kDa. Optimal pH and temperature were 5.5 and 65 °C, and completely stable over the pH range of 5.0 to 8.0. The enzyme retained about 85% of its initial activity after 8 h of incubation at 55 °C, with t1/2=27 h. Enzyme incubation at 60 and 65 °C resulted in t1/2 of 0.3 and 1.5 h, respectively. Kinetic parameters for the hydrolysis of pNPGlc were Vmax=715.3 ± 58.9 U mg− 1 and Km=69.9 ± 4.6 µmol L− 1. Increasing xylose concentrations up to 200 mmol L− 1 increased enzyme activity 1.53-fold, reaching a Vmax of 1,098.4 ± 75.8 U mg− 1, with a Km of 1.7 ± 0.1 mmol L− 1. Ethanol increased relative activity up to 30% in the presence of 10% (v/v) ethanol, and xylose stimulated activity by 53% at 50 mmol L− 1, suggesting potential compatibility with bioethanol process streams. The high thermal and pH stability of BglHb, combined with its stimulation by xylose and ethanol, suggests great potential for application in lignocellulosic biomass saccharification.