Influence Of Acidity And Urea On The Interaction Between Bovine Serum Albumin And Small Molecule

Studies on the mechanism of the binding between small molecule and biological macromolecule were shown to have great significance, especially in the fields of investigating the structure and the function of biology molecule and clarifying the metabolic process. The structure and conformation of Bovine Serum Albumin (BSA) were found to transform in the presence of different denaturants, hence, its ability to bind other medicine molecules would change accordingly. The work focused on the influence of acidity and urea on the binding between BSA and small molecule using ultraviolet-visible spectrum and fluorescence spectrum. The main contents are as follows:1. BSA is known to exist as N (native, pH=5.0～7.0), B (basic, pH=7.0～9.0), F(partially acid expanded, pH=5.0～3.5)and E (expanded, pH<3.5) isomeric forms in solution of different pH. The reaction mechanism between methyl red (MR) and BSA was investigated with fluorescence spectra. The results showed that the synchronous fluorescence spectra of Trp had blue shift and were quenched in the presence of MR. While without obvious shift to Tyr, the fluorescence intensity of Tyr decreased when the concentration of MR was lower2. The acidic effect on the structure of BSA and the interaction of different structure of BSA with Oflxacin was studied with UV-vis and fluorescence spectra. Based on the fluorescence quenching of BSA and F(o|¨)rster energy transfer mechanism, quenching constants, energy transfer efficiencies and the binding distances were determined under four different pHs. It was found that non-radiative energy transfer and static quenching were the cause of fluorescence quenching. It was not obviously observed the influence of neutral, subacidity and alkalescent conditions on the binding of Oflxacin and bovine serum albumin and electrostatic interaction was not the main force. The effect of Oflx on the conformation of BSA was also investigated using synchronous fluorescence Spectrometry3. The binding mechanism of interaction of silver colloids with BSA has been investigated. The decrease, increasing peak width at half height and red shift of 399 ran surface plamon band of silver colloids indicated that the BSA could be absorbed on the surface of silver colloids. The process of quenching the fluorescence of BSA by colloidal silver was determined to be a static quenching process. It was found that the intensity of binding between silver colloids and BSA was greater than other small molecule binding to BSA. It can be speculated that the binding forces between silver colloids and BSA should be electrostatic and hydrophobic interaction. A big binding constant and a large numbers of coverage have been found under acidic solution. A particular twofold hysteresis effects were significantly found with the coverage of aggregated nanoparticles and the conformational transition of BSA, respectively.4. Structural alteration of urea-induced BSA and interaction of Oflxacin with urea-induced BSA were investigated with UV-vis and fluorescence spectroscopy . The results indicated that BSA followed a two-step, three-state transition with an intermediate in process of unfolding. With increasing the concentration of Urea, it can be found that the fluorescence of BSA decreased with a blue shift of about 8 nm (from 344 nm to 336 nm) firstly, and subsequently a red shift to 350 nm. When urea concentrations varied from 4.6 mol/L to 5.2 mol/L, a strong quenching effect of Oflx on the fluorescence of intermediate of BSA was found under the optimal condition as fluorescence quenching constants (K_Q)=10.46×10⁴ L/mol, C_urea=4.8 mol/L, and binding constants (K_A=3.881×10⁵ L/mol, Urea 4.8 mol/L), whereas with small binding sites (n=0.76) under urea 5.0 mol/L and low energy transfer efficiency (E=0.3002) under urea 4.8 mol/L. Synchronous fluorescence Spectrometry showed that during unfolding of BSA induced by urea, Trp-212 residue microenvironment had no changes, at the same time the maximal fluorescence peak of Tyr shifted towards short-wavelength. The introduction of Oflx made Trp microenvironment more hydrophodic, and also accelerated the denaturation of BSA by urea.In a word, the study of the interaction between serum albumin and drugs is a very important task in the fields of life science and chemistry, which helps us to understand the mechanism and disciplinarian of the reactions between the protein and the small molecules at the molecular level.