Enhancing Catalytic Performance of Porcine Pancreatic Lipase by Covalent Modification Using Functional Ionic Liquids

Various functional ionic liquids (ILs) composed of different cations and anions were activated with carbonyldiimidazole and then covalently linked onto porcine pancreatic lipase (PPL) through lysine coupling. Catalytic performances, such as activity, thermostability, and enantioselectivity were improved successfully, as was investigated in p-nitrophenyl palmitate (pNPP) hydrolysis and racemic 1-phenethyl acetate hydrolysis reaction. The correlation between catalytic performance and modification of IL was studied by catalytic and spectroscopic data, which showed improvement of catalytic performances to a different extent. Hydrolytic activity was enhanced by ILs with chaotropic cations and kosmotropic anions (e.g., more than 4-fold with [choline]-[H2PO4]). Modifications by ILs bearing kosmotropic cations and chaotropic anions contribute to lipase thermostability and enantioselectivity (e.g., modification with [HOOCBMIm][Cl] showed a 12-fold thermostability increase at 60 degrees C and more than 7-fold enantioselectivity enhancement than native enzyme). The Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry experiments suggest that ILs bind with lipase protein. Conformation changes were confirmed by fluorescence spectroscopy, and circular dichroism spectroscopy.