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

Abstract

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