Immobilization of cellulase on styrene/maleic anhydride copolymer nanoparticles with improved stability against pH changes

A facile strategy to immobilize cellulase was developed in this work. Firstly, crosslinked styrene and maleic anhydride copolymer nanoparticles (SMN) were conveniently synthesized as carrier by self-stable precipitation polymerization in the absence of any stabilizer. Benefit from the high reactivity of anhydride groups, the cellulase was then covalently bound to SMN at mild condition. The optimum loading amount of cellulase on SMN was determined to be 167 mg/g. Although the immobilized cellulase showed almost no change of activity at temperature from 30 °C to 80 °C compared to free cellulase, its pH stability was significantly improved. After immobilization, the optimum pH shifted to 5.0 and immobilized cellulase could retain 80% activity at pH 8.0, which was much higher than that of free enzyme (14%). Furthermore, the immobilized cellulase showed excellent reusability in catalytic hydrolysis of carboxymethylcellulose sodium salt, preserving almost 100% activity after recycling 6 times and loss only 20% activity after 10 cycles. The results suggest that SMN is a promising carrier for enzyme immobilization.