CelB and β-glucosidase immobilization for carboxymethyl cellulose hydrolysis

Abstract

Cellulose hydrolysis is an important step in the production of bioethanol from cellulosic biomass. Two key cellulase enzymes, celB and β-glucosidase, were covalently immobilised on polystyrene treated with plasma immersion ion implantation (PIII) which creates radicals that form covalent bonds. The immobilized enzymes were used to produce glucose from carboxymethyl cellulose (CMC), a solubilised form of cellulose. CelB from Caldicellulosiruptor saccharolyticus is a thermophilic cellulase with both endoglucanase and exoglucanase activity. The highest activity of the immobilised celB on PIII treated surfaces was achieved when their immobilisation is carried out at a pH in the range 5–6.5. The immobilized celB on the PIII treated surface had the same activation energy as free celB showing substrate accessibility is not affected by the presence of the surface. The V_max and K_m values of immobilized celB were found to be comparable to those of equal free celB concentrations. The areal density of immobilized celB on the PIII treated surface was estimated to be 0.3 μg cm⁻². The polystyrene surface with immobilized celB at 45 °C could be reused over four times (23 hours each) with approximately 30% total activity loss. High ratios of β-glucosidase to celB were found to enhance the activity of immobilized celB for CMC hydrolysis.