Interaction Between Fulvic Acid and Pepsin Investigated by Multispectral and Molecular Docking Simulation †

doi:10.7503/cjcu20190252

Abstract

Abstract:

The interaction of fulvic acid(FA) with pepsin(PEP) was investigated using fluorescence spectra, UV-Vis absorption spectra, three-dimensional fluorescence spectra, synchronous fluorescence spectra, Fourier transform infrared spectroscopy, circular dichroism and molecular docking simulation method. Fluorescence spectrum analyses shows that the type of fluorescence quenching by FA-PEP is static quenching. According to the Stern-Volmer equation and the static quenching double logarithmic formula, the quenching constants(K_sv) and the number of binding sites(n) were calculated. According to the Vant’t Hoff equation, the thermodynamic parameters were calculated to be ΔH=-59.86 kJ/mol, ΔS=-98.13 J·mol ^-1·K ^-1 and ΔG=-30.62 kJ/mol(298 K). Thermodynamic analysis suggests that hydrogen bonds and van der Waal’s forces are the main forces between PEP and FA, and the interaction is spontaneous process. According to the theory of F?rster’s non-radiative energy transfer, the binding distance between PEP and FA was calculated to be 2.436 nm, implying that non-radiative energy transfer occurs between FA. The molecular docking simulation technique displays that the binding force of FA-PEP includes not only hydrogen bonds and van der Waals forces but also hydrophobic interaction forces.

Key words: Fulvic acid, Pepsin, Multispectroscopy, Molecular docking simulation method

CLC Number:

O657.3

TrendMD:

WANG Xiaoxia, MA Litong, NIE Zhihua, WANG Zhengde, CUI Jinlong, ZHAO Wenyuan, SAI Huazheng. Interaction Between Fulvic Acid and Pepsin Investigated by Multispectral and Molecular Docking Simulation ^†[J]. Chem. J. Chinese Universities, 2019, 40(9): 1840.

Figures/Tables 10

Fig.1 Fluorescence quenching spectra of FA-PEP interaction system at 298 K

T/K	10^-4K_sv/ (L·mol^-1)	10^-12K_q/ (L·mol^-1·s^-1)	10^-5K_A/ (L·mol^-1)	Binding-site number, n	ΔH/ (kJ·mol^-1)	ΔS/ (J·mol^-1·K^-1)	ΔG/ (kJ·mol^-1)
298	9.906	9.906	2.421	1.368			-30.62
303	9.089	9.089	1.435	1.322	-59.86	-98.13	-30.12
308	8.860	8.860	1.107	1.294			-29.63

Fig.2 Overlapping of the fluorescence spectrum of PEP(a) with the absorption spectrum of FA(b) a. c(PEP)=5.0×10-5 mol/L; b. c(FA)=5.0×10-5 mol/L. T=298 K, pH=2.0.

Fig.3 Synchronous fluorescence of FA and PEP (1)Δλ=15 nm; (B) Δλ=60 nm. c(PEP)=5.0×10-5 mol/L. 104c(FA)/(mol·L-1): a—i. 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. T=298 K, pH=2.0.

Fig.4 UV spectra of FA and PEP c(PEP)=6.0×10-4 mol/L; 104c(FA)/(mol·L-1): a—i. 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. T=298 K, pH=2.0.

Fig.5 Three-dimensional fluorescence spectra(A) and contour diagrams(B) of PEP c(PEP)=5×10-5 mol/L, T=298 K, pH=2.0.

Fig.6 Three-dimensional fluorescence spectra(A) and contour diagrams(B) of FA-PEP system c(PEP)=5×10-5 mol/L, c(FA)=5×10-5 mol/L, T=298 K, pH=2.0.

Fig.7 Circular dichroism spectra of the PEP-FA system a. c(PEP)=5.0×10-5 mol/L, c(PEP)∶c(FA)=1∶0; b. c(PEP)=5.0×10-5 mol/L, c(FA)=2.5×10-4 mol/L, c(PEP)∶c(FA)=1∶5. T=298 K, pH=2.0.

Fig.8 Infrared spectra of PEP(a) and FA-PEP system[m(PEP)∶m(FA)=1∶1](b) at 298 K

Fig.9 Molecular docking simulation of FA and PEP

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