Diazobicyclo[5.4.0]undec-7ene-ium and tetramethyl guanidium based ionic liquids enhanced thermal stability of xylose reductase at extreme pH through specific ion effect

Abstract

As part of sustainable industrial bioprocesses, conversion of xylose from lignocellulosic biomass residues has gained attention and importance over recent decades. Xylitol is one such imperative metabolites which can be obtained in a single step conversion from xylose through enzymatic process employing xylose reductase. Xylose reductase from Debaryomyces nepalensis NCYC 3413 (DnXR) has proved to be potential candidate for this purpose due to its industrially superior characteristics compared to the enzymes from other sources. Ionic liquids have applications in various fields, especially in biotechnology, as a replacement of organic solvents as well as for efficient processes and improvement of existing process by enhancing the stability of biomolecules. In this study, effect of diazobicyclo[5.4.0]undec-7ene-ium (DBU), tetramethyl guanidium (TMG) based and Cholinium based ionic liquids on the activity and stability of DnXR was investigated in terms of thermodynamic parameters, half-life time as well as the intrinsic tryptophan fluorescence at pH 5.0, 7.0 and 10.0. [TMG][But] and [DBU][Acetate] were effective in improving the enzyme activity at pH 10.0 by 72% and 58%. [TMG][Acetate] increased the functional stability at pH 10.0 by 10-fold while maintaining the activity same as control and [DBU][Chloride] enhanced the half-life time by 8.5-fold at pH 5.0.