Immobilization of Bacillus subtilis esterase by simple cross-linking for enzymatic resolution of dl-menthyl acetate

A recombinant esterase (EC 3.1.1.1) cloned from Bacillus subtilis 0554 (BSE) was carrier-freely immobilized with the method of cross-linked enzyme aggregates. The conditions for preparing the cross-linked aggregates of BSE (CLA-BSE) were optimized, including the type and concentration of precipitants, and the concentration of cross-linker, and a simple and efficient procedure for preparing CLA-BSE was developed, consisting of a precipitation step with 0.5 g mL−1 (NH4)2SO4 and a cross-linking step with 60 mM glutaraldehyde for a period of 3 h as the cross-linking time. As a result, about 70% of the initial free BSE activity was incorporated into the CLA-BSE. The thermal stabilities of the immobilized enzyme at 30 °C and 50 °C were >360 and 14 times those of free BSE, respectively. More importantly, the operational stability of CLA-BSE was also considerably improved. In the kinetic resolution of dl-menthyl acetate to produce l-menthol with CLA-BSE gave eep > 94% at conversion of >40% and the CLA-BSE could be reused for 10 times with only about 8% reduction in activity. Therefore, the new biocatalyst immobilized through the methodology of CLEAs could significantly decrease the manufacturing cost of l-menthol and would be more beneficial for its practical applications.

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► A Bacillus subtilis esterase was immobilized by simple method.
► Thermal stability of immobilized esterase was significantly improved.
► Immobilized esterase was reused for 10 times with only about 8% reduction in activity.
► Immobilized enzyme exhibited high enantioselectivity and conversion.