Structural evidence for kinetic and thermal stability changes of α-amylase due to exposure to [emim][lactate] ionic liquid

Abstract

Objectives: α-amylases hydrolyze α-1,4 glycosidic bondsin starch. ILs used as co-solvent in different enzymatic reactionsto improve activity, selectivity and stability of enzymes.In this study, fluorescence spectroscopy methodwas used to explain the effect of [emim][lactate] on kineticand thermal stability of Aspergillus oryzae α-amylase.Methods: Effect of different concentrations of [emim][lactate] on activity of α-amylases was determined. Kineticparameters, optimum pH and temperature and thermalstability were determined and compared with absence of[emim][lactate]. Intrinsic fluorescence spectroscopy for Trpresidues was performed for both presence and absence of[emim][lactate].Results: Activity of α-amylase decreases in presence of[emim][Lac]. Moreover, Km of α-amylase in the presence of[emim][lactate] increases while Vm decreased. Optimumtemperature in presence of [emim][lactate] increases from45 to 50 °C while optimum pH decreases from 9 to 7.Thermal stability of α-amylase in the presence of [emim][lactate] is similar to that in the absence of [emim][lactate]at 40 and 50 °C but decreases at 60 °C. Intrinsic fluorescencespectroscopy shows unfolding of native structure ofα-amylase is dependent on [emim][lactate] concentration.Conclusions: Presence of [emim][lactate] ionic liquid asco-solvent leads to structural unfolding of α-amylase andloss of its activity and thermal stability.