Recyclable Soluble-Insoluble Upper Critical Solution Temperature-type Poly(methacrylamide-co-acrylic acid)-Cellulase Biocatalyst for Hydrolysis of Cellulose into Glucose

摘要

How to improve the accessibility of immobilized cellulase to insoluble cellulose and recover immobilized enzyme from remaining insoluble substrate is a challenge to the efficient hydrolysis of cellulose into glucose. The objective of this work is to solve the problems mentioned above by the immobilization of cellulase onto poly(methacrylamide-co-acrylic acid) (PMAAc), developing a reversibly soluble-insoluble biocatalyst with upper critical solution temperature (UCST) of 16 degrees C. The as-prepared PMAAc-cellulase with a new UCST of 19 degrees C exhibited significantly improved pH, temperature, storage, and operation stabilities compared with that of free catalyst, and about 82.4% of its original activity was retained even after ten cycles. Cellulase systems containing endo-beta-1,4-glucanase (EG), cellobiohydrolase (CBH), and beta-glucosidase (beta-G) are coimmobilized at an optimum ratio on PMAAc by adjusting the additive amount of beta-G, which can obtain higher hydrolysis efficiency. It was found that the coimmobilization of cellulase and beta-glucosidase at the optimum ratio of 2.5:1 (w/w) showed excellent performance for the hydrolysis of cellulose, and the yield of glucose was up to 89.1% at 50 degrees C (UCST) after 24 h, which was 58.4% and 15.4% higher than that of PMAAc cellulase and free cellulase and beta-glucosidase, respectively. The coimmobilized PMAAc cellulase and beta-glucosidase still retained 61.48% of its original productivity after eight cycles of hydrolysis. This novel UCST-type polymer enzyme catalytic system displays great potential in cellulose biorefining.