Xylanase immobilization on modified superparamagnetic graphene oxide nanocomposite: Effect of PEGylation on activity and stability.

In order to utilize the advantages of immobilization such as improvement of stability, increasing the catalytic activity, ability to recovery and reuse of enzyme from reaction medium, xylanase enzyme was immobilized on superparamagnetic garphene oxide nanosheets (GOMNP). Xylanase, as a hydrolytic enzyme of xylan has widely used in industry. Since the xylan is bulk, for enhance accessibility of active sites of the immobilized xylanase, polyethylene glycol bis amine (PEGA) was used as a spacer for functionalization of GOMNP. The modified GOMNP and immobilized xylanase on PEGA-GOMNP (PEGA-GOMNP/Xy) were characterized through different analysis tools. The results showed that xylanase was attached to the functionalized nanocomposite with a yield of 273mg enzyme per gram PEGA-GOMNP. Thermal stability, pH stability, reusability and storage stability were determined for immobilized enzyme. The free and immobilized xylanase displayed an optimal enzymatic activity at 60°C and pH 6.5 and 7.5, respectively. The immobilized enzyme retained about 40% of the initial activity after 8 cycles with xylan substrate at 60°C. Also immobilized and free enzymes retained 35% and 20% of the initial catalytic activity after 90days storage at 4°C, respectively. Consequently, PEGA- modified GOMNP can be introduced as a biodegradable and suitable support for bioengineering.