Abstract: The stability of lipase in ionic liquid and supercritical fluid system is the most important factor for its activity.In this paper,molecular dynamic simulation method was employed to research the structure and performance of candida antarctica lipase B (CALB) in ionic liquid CYPHOS IL-201/polar supercritical fluid (CHF₃) and CYPHOS IL-201/nonpolar supercritical fluid (CO₂) biphasic systems.The results showed that,in the supercritical fluid CHF₃ system,hydrogen bonds that kept the α-helix structure stable were destroyed,which was the main reason for the unstable structure of protein;in the supercritical fluid CO₂ system,the structural tightness of CALB protein reduced and the secondary structure of protein changed,which resulted in the decreased stability of protein.The ionic liquid and the supercritical fluid formed biphasic systems in which the former (protein dissolved in it) was insoluble in the latter,but part of the supercritical fluid entered the ionic liquid phase,and reduced the viscosity of the ionic liquid phase.The viscosity of CYPHOS IL-201/CHF₃ system decreased more than that of CYPHOS IL-201/CO₂ system.In the CYPHOS IL-201/supercritical fluid (CHF₃ or CO₂) biphasic systems,the ionic liquid CYPHOS IL-201 played a key role in protecting the structure of protein,which resulted in more stability of CALB protein.

Key words: candida antarctica lipase B, ionic liquid, supercritical fluid, molecular simulation