Immobilized L-ribose isomerase for the sustained synthesis of a rare sugar D-talose

Abstract

• L-ribose isomerase (L-RI) immobilized on carbon nanomaterials. • L-RI enzyme loaded to the extent of 72–75% on CNMs. • The immobilized biocatalyst governed 12–14% bioconversion of D -tagatose to D -talose. • The immobilized L -RI can be efficiently recycled for 8–10 times. The biocatalytic enactment of immobilized enzyme mainly depends on the essential properties of the matrix and enzyme as well as on immobilization process and immobilization conditions. Carbon based nanomaterials (CNMs) such as graphene oxide (GOx) and multiwalled carbon nanotubes (MWCNT) preserve unique properties for enzyme immobilization via covalent conjugation and physical adsorption. L -ribose isomerase (L-RI) was immobilized on GOx and MWCNT through covalent linkage and surface adsorption. The hybrid composition of biocatalyst was characterized. Immobilization of L -RI (1 mg mL −1 ) on 0.05 mg GOx showed maximum relative activity with 70–75% loading of L -RI via the covalent (GOx@Co- L -RI) and adsorption (GOx@Ad- L -RI) method. On the other hand, 0.15 and 0.1 mg of MWCNT was found to be efficient for the immobilization of L -RI. Effect of different operational conditions like enzyme support ratio, immobilization time, and temperature was also investigated. Optimized conditions were used to study enzyme kinetics, reusability, biocatalytic conversion, metal ion effect, pH and temperature. Under optimized conditions, 72–75% of L -RI enzyme loading was achieved on CNMs via covalent conjugation and physical adsorption. Covalent linkage of L -RI with nanosupport (GOx and MWCNT) was observed to be the best for maximum relative activity. The catalytic efficiency (k cat ) of L -RI was increased by more than two-fold upon immobilization. The bioconversion of D -tagatose to D -talose by immobilized biocatalyst was 12–14%. The immobilized L -RI was found to be efficiently recycled for 8 times. After 8 cycles of reuse, activity recovery of L -RI immobilized on GOx and MWCNT was 55% and 41%, respectively.