Interaction between hesperetin and human serum albumin revealed by spectroscopic methods

Study on the binding of luteolin to bovine serum albumin

Binding of luteolin (LU) to bovine serum albumin (BSA) was investigated at 298, 308 and 318K at pH 7.4 using spectrophotometric techniques such as fluorescence emission, circular dichroism (CD). The data obtained from fluorescence quenching experiments showed that LU was bound to BSA and binding constants and the number of binding sites (n approximately 1) were obtained. The thermodynamic parameters DeltaH(0), DeltaS(0), DeltaG(0) at different temperatures were calculated. They indicated that both hydrophobic forces and hydrogen bonds are the major interactions between LU and BSA. A value of 3.12nm for the average distance r between LU (acceptor) and tryptophan residue (Trp) of BSA (donor) was derived from the fluorescence resonance energy transfer. The effects of some common metal ions on the binding are also considered. Besides, the interaction of BSA with LU led to a change in the conformation of BSA.

Interaction of brilliant red X-3B with bovine serum albumin and application to protein assay

The interaction of brilliant red X-3B (BRX) with bovine serum albumin (BSA) in three pH media has been characterized by the spectral correction technique. The binding number maximum of BRX was determined to be 102 at pH 2.03, 82 at pH 3.25 and 38 at pH 4.35 and the binding mechanism was analyzed in detail. The effects of ionic strength from 0 to 1 mol L(-1) and temperature from 20 to 70 degrees C on the binding were investigated. The results showed that the interaction of BRX with BSA responded to the Langmuir adsorption isothermal model and the binding constant was determined. From the correlation between the binding number and the number of basic amino acid residues, the ion-pair attraction induced the union of non-covalent bonds including H-bond, van der Waals force and hydrophobic bond and the binding model was illustrated. The binding of BRX to BSA has resulted in change of the BSA conformation confirmed by means of circular dichroism. Using this interaction at pH 2.03, a sensitive method named the absorbance ratio difference spectrometry was established and applied to the protein assay and the limit of detection of protein was only 6 microg L(-1). Two samples were determined and the results were in agreement with those obtained by the classical coomassie brilliant blue colorimetry.

Study on the Interaction between the chiral drug of propranolol and α1-acid glycoprotein by fluorescence spectrophotometry

The interaction between the chiral drug of propranolol (PPL) and alpha1-acid glycoprotein (AGP, orosomucoid) has been first studied by fluorescence spectrophotometry. The fluorescence intensity of PPL increased due to the addition of AGP into PPL. The equation of Scatchard was employed to calculate the association constant and binding site number of the two enantiomers with AGP. The association constant is 2.62 x 10(5)M-1 for R-PPL and 8.57 x 10(5)M-1 for S-PPL and the binding site number is 0.41 for R-PPL and 1.17 for S-PPL at 17 degrees C respectively. The method of thermodynamics was applied to determine the binding type of S-PPL with AGP. The results suggested that the binding type is mainly van der waals force or hydrogen bond. At last the effect of three metal cations on the association constant and the binding site number of S-PPL with AGP was examined.

Protein Secondary Structure Controlled with Light and Photoresponsive Surfactants

The interaction of a light-responsive azobenzene surfactant with bovine serum albumin (BSA) has been investigated as a means to examine photoreversible changes in protein secondary structure. The cationic azobenzene surfactant undergoes a reversible photoisomeriztion upon exposure to the appropriate wavelength of light, with the visible-light (trans) form being more hydrophobic and, thus, inducing a greater degree of protein unfolding than the UV-light (cis) form. Fourier transform infrared (FT-IR) spectroscopy is used to provide quantitative information on the secondary structure elements in the protein (alpha-helices, beta-strands, beta-turns, and unordered domains). Comparing the secondary structure changes induced by light illumination in the presence of the photoresponsive surfactant with previous measurements of the tertiary structure of BSA obtained from small-angle neutron scattering (SANS) allows the three discrete conformation changes in BSA to be fully characterized. At low surfactant concentrations, an alpha-helix --> beta-structure rearrangement is observed as the tertiary structure of BSA changes from a heart-shaped to a distorted heart-shaped conformation. Intermediate surfactant concentrations lead to a dramatic decrease in the alpha-helix fraction in favor of unordered structures, which is accompanied by an unfolding of the C-terminal portion of the protein as evidenced from SANS. Further increases in photosurfactant concentration lead to a beta --> unordered transition with the protein adopting a highly elongated conformation in solution. Each of these protein conformational changes can be precisely and reversibly controlled with light illumination, as revealed through FT-IR spectra collected during repeated visible-light <--> UV-light cycles.

Characterization of the interaction between human serum albumin and morin

The interaction of morin with human serum albumin (HSA) has been investigated by using fluorescence, UV absorption and Fourier transform infrared spectroscopic approaches for the first time. Fluorescence data revealed the presence of a specific binding site on HSA for morin, and the binding affinity was 1.13+/-0.11x10(-5) L Mol(-1) in the physiological condition. The intrinsic fluorescence of morin was conspicuously enhanced in the presence of HSA due to excited-state proton transfer. The binding ability of morin to protein decreased with the increase of the buffer pH from 6.4 to 8.4, which signified that the level of protonation of the hydroxyl groups played an important role during the drug-protein binding process. From the UV absorption spectra of morin in various pH medium, the dissociation behaviors of the hydroxyl groups on the drug molecule were assigned. The second derivative UV absorption spectra of morin after interacting with HSA were used to elucidate the binding mode of morin to protein. The obvious red shift of the UV absorption band I of morin upon binding to HSA further confirmed the formation of HSA-morin complex, and this property was also utilized to estimate the binding constant. The interaction between morin and HSA induced an obvious reduction of the protein alpha-helix and beta-sheet structures.

Interaction of Non-Steroidal Anti-Inflammatory Drugs, Etoricoxib and Parecoxib Sodium, with Human Serum Albumin Studied by Fluorescence Spectroscopy

The mechanism of interaction of the non-steroidal anti-inflammatory drugs, etoricoxib and parecoxib sodium, with human serum albumin (HSA) was studied using fluorescence spectroscopy. There was only one class of binding site with association constants of the order of 10(4). Thermodynamic parameters suggest that van der Waals and hydrogen bonding interactions in the case of etoricoxib, and electrostatic and hydrogen bonding interactions in the case of parecoxib sodium, are predominantly involved in the binding. Studies in the presence of the hydrophobic probe, 1-anilinonaphthalene-8-sulfonate (ANS), showed that hydrophobic interactions are not involved in the binding of these drugs to HSA. Displacement studies using the site-specific probe, dansylsarcosine piperidinium salt (DSS), showed that the drugs are bound at site II on the HSA molecule. However, etoricoxib and parecoxib sodium are bound at different regions within site II. Increase of pH and the presence of salt caused significant changes in the association constants and the concentration of free pharmacologically active drug. Stern-Volmer analysis of the binding data indicated that the tryptophan residues of albumin are not fully accessible to anionic parecoxib sodium and a predominantly static quenching mechanism is operative in each case.