Influence of Bovine Liver Catalase on Self-Assembled Structures of a Surface-Active Ionic Liquid

Abstract

The modulation of self-assembled structures of a surface-active ionic liquid (SAIL), 1-butyl-3-methylimidazolium octyl sulfate [C₄mim][C₈OSO₃], upon their interaction with bovine liver catalase (CAT) enzyme is investigated in this study. The intrinsic fluorescence of tryptophan (Trp) was investigated to monitor the conformational changes in CAT with [C₄mim][C₈OSO₃]. Extrinsic fluorescence of the 8-anilino-1-naphthalenesulfonic acid (ANS) probe was further utilized to determine the structural and conformational changes along with the binding location of [C₄mim][C₈OSO₃] in the enzyme. Fourier transform infrared (FTIR) measurements quantify the secondary structure changes, leading to modulation in the fluorescence characteristics. To elucidate modulation of the self-assembled structures, fluorescence lifetime imaging microscopy (FLIM) measurements were utilized. On adding CAT to an aqueous micellar solution of [C₄mim][C₈OSO₃], there was the appearance of highly fluorescent ring-like structures. The internal structure of these was further investigated using transmission electron microscopy (TEM), where the ring sizes were found to be dependent upon the quantity of enzyme taken. These structures completely collapse and accumulate when the CAT concentration reaches near ∼5–7 μM. Further, the activity of the CAT enzyme was assessed in the presence of [C₄mim][C₈OSO₃] depending upon the premicelle and micelle self-assemblies. Molecular dynamics (MD) simulation study was used to further analyze the binding location of the micelle-forming entity, [C₈OSO₃], and it was found that the [C₈OSO₃] species tends to remain at the enzyme active site. The results describe the unique transformation in self-assemblies of a SAIL by enzymatic action that has not been studied so far and opens up the interesting applications of SAIL in biomedical applications.