Screening of Ionic Liquids and Deep Eutectic Solvents for Enhancing the Activity and Stability of Fungal Laccase: Empowering Kinetic Parameters and Long-Term Conservation

Ionic liquids (ILs) and deep eutectic solvents (DESs) are currently of great interest due to their highly interesting physicochemical properties; they were studied throughout many chemical and biological approaches, and they were used intensively in biocatalysis and biomedicine.In the present study, ten synthesized ILs and four synthesized DESs have been used to study their effect on the laccase enzyme. Hence, ILs and DESs have been screened in a conventional reaction-buffered medium (25 °C and pH 7.0) and using ABTS and DMP as substrates to study the catalytic ability and the stability of the enzyme. From 14 newly synthesized materials, only three water-miscible ILs ([BMIM][Ac], [Chol][Ac], and [Chol][Prop]) and one DES ([Chol][Ac.Ox]) have shown interest in improving the enzyme activity and stability. Among them, [BMIM][Ac] has shown impressive empowering power for the laccase activity (almost a 20-fold enhancement versus control); however, it was not efficient to protect the enzyme against high temperature or long conservation. The two choline-based ILs, [Chol][Ac] and [Chol][Prop], have allowed the increase of laccase activity with a rate of 1.7-fold and 7.8-fold, respectively, and they were shown to have interesting properties to protect the enzyme against temperature and storage. Regarding the DES [Chol][Ac.Ox], it improved the laccase at about 8.9-fold, but this rate has not been stable along the experiment due to the high hydrophobic nature of the solution; it could be more useful when applied at high temperatures. The four screened compounds in general improved the activity of the enzyme, especially at pH 7.0, and showed a great sensitivity against temperature. By kinetic studies versus [BMIM][Ac], it was demonstrated that the IL can improve the laccase activity by increasing the catalytic markers (Vm and Kcat); however, a decrease of the affinity has been noted by Km decreasing, which testifies that the interaction of the enzyme with ILs can affect the proteinic structure in an aqueous medium.