Screening of newly synthesized Ionic Liquids and Deep eutectic solvent for enhancing the activity and stability of fungal laccase: empowering kinetic parameters and long-term conservation

Ionic Liquids (ILs) and Deep Eutectic Solvents (DES) are currently with great interest due to their highly interesting physicochemical properties, it was studied throughout many chemical and biological approaches and it was used intensively in biocatalysis and biomedicine. In the present study, 10 newly synthesized ILs and 04 newly synthesized DES has been used to study their effect on laccase enzyme. Hence ILs and DES have been screened in 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 synthetized items, only three water-miscible ILs ([BMIM][Ac], [Chol][Ac], and [Chol][Prop]) and one DES ([Chol][Ac.Ox]) have shown interest for improving the enzyme activity and stability. Among them, the [BMIM][Ac] has shown impressive empowering power for the laccase activity (almost 20 folds 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 folds and 7.8 folds, respectively and it was shown interesting properties to protect the enzyme against temperature and storage. Regarding the DES [Chol][Ac.Ox], it was improved the laccase at about 8.9 folds 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 in high temperature. The four screened items in general improved the activity of the enzyme especially at pH7.0 and shown 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 notified by Km decreasing, which testify that the interaction of the enzyme with ILs can affect the proteinic structure in aqueous medium.