Investigation of the Interaction of Pepsin with Ionic Liquids by Using Fluorescence Spectroscopy

Abstract

The molecular mechanism of the interaction between pepsin and two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-octyl-3-methylimidazolium chloride ([C8mim]Cl), was investigated with fluorescence spectroscopy, ultraviolet absorption, and circular dichroism spectroscopy at a pH value of 1.6. The results suggest that ILs could quench the intrinsic fluorescence of pepsin, probably via a dynamic quenching mechanism. The fluorescence quenching constants were determined by employing the classic Stern-Volmer equation. The constant values are very small, indicating that only a very weak interaction between ILs and pepsin exists. The Gibbs free-energy change, enthalpy change (ΔH), and entropy change (ΔS) during the interaction of pepsin and ILs were estimated. Positive values of ΔH and ΔS indicate that the interaction between ILs and pepsin is mainly driven by hydrophobic interaction. Synchronous and three-dimensional fluorescence spectra demonstrate that the addition of ILs (0-0.20 mol L(-1) for each IL) does not bring apparent changes to the microenvironments of tyrosine and tryptophan residues. Activity experiments show that the activity of pepsin is concentration dependent; higher concentrations of ILs (>0.22 mol L(-1) for [C8mim]Cl and >0.30 mol L(-1) for [C4mim]Cl) cause the remarkable reduction of enzyme activity. The presence of ILs also does not improve the thermal stability of pepsin.

Kinetics and mass spectrometric measurements of myoglobin unfolding in aqueous ionic liquid solutions

“…Significant data exists to enable design of ILs for many non-biochemical applications [33], but researchers are just beginning to compile comprehensive IL/protein data for prediction and design of biochemical/biomedical applications. A number of groups have studied different ILs series and their effects on protein stability [11,16,[34][35][36], IL-protein surface interactions [9,26,37,38], and protein thermodynamic stability in aqueous IL solutions [5,7]. Low-concentration ILs in aqueous solution often do not denature proteins, but can destabilize their structures as demonstrated by numerous thermodynamic studies [5,7,8,10,15,39].…”

Efficient synthesis of cefadroxil in [Bmim][NTf2]‐phosphate cosolvent by magnetic immobilized penicillin G acylase

“…The analytical results by fluorescence spectroscopy found that the maximum of fluorescence intensity of excitation spectrum or the emission spectrum of free PGA occurred at the [Bmim][NTf 2 ] concentration of 62.5% (v/v) as shown Figure , and the variation of the fluorescence intensity was consistent with that of the synthesis activity of PGA‐PM@Fe 3 O 4 in the cosolvent with different concentrations of [Bmim][NTf 2 ]. The intrinsic fluorescence spectrum is mainly attributed to aromatic amino acids (Trp, Tyr, and Phe) on side chains of the tertiary structure of enzyme protein . Therefore, the variation of fluorescence intensity for PGA could reflect the degree of changes in its tertiary structure in different concentration of [Bmim][NTf 2 ] in the cosolvent.…”

Probing the Interaction between Acotiamide Hydrochloride and Pepsin by Multispectral Methods, Electrochemical Measurements, and Docking Studies

“…One is Peak a and it is the Rayleigh scattering peak (λ em = λ ex ). The other is Peak I (λ ex /λ em = 280/336 nm), which mainly reveals the spectral feature of Tyr and Trp residues [34]. The intensity of Peak a increased with the addition of acotiamide hydrochloride, as shown in Table 3.…”