Spectroscopic investigation on the interaction of salidroside with bovine serum albumin

Inhibition and Mechanism of Protein Nonenzymatic Glycation by Lactobacillus fermentum

Lactobacillus fermentum (L. fermentum) was first evaluated as a potential advanced glycation end-product (AGE) formation inhibitor by establishing a bovine serum albumin (BSA) + glucose (glu) glycation model in the present study. The results showed that the highest inhibition rates of pentosidine and total fluorescent AGEs by L. fermentum were approximately 51.67% and 77.22%, respectively, which were higher than that of aminoguanidine (AG). Mechanistic analysis showed that L. fermentum could capture methylglyoxal and glyoxal, inhibit carbonyl and sulfhydryl oxidation, reduce the binding of glucose and amino groups, increase total phenolic content and antioxidant activity, and release intracellular substances to scavenge free radicals; these abilities were the basis of the antiglycation mechanism of L. fermentum. In addition, L. fermentum significantly prevented conformational changes in proteins during glycation, reduced protein cross-linking by 35.67%, and protected the intrinsic fluorophore. Therefore, the inhibition of L. fermentum on glycation mainly occurs through antioxidation, the capture of dicarbonyl compounds, and the protection of the BSA structure. These findings collectively suggest that Lactobacillus is an inhibitor of protein glycation and AGE formation and has the potential for nutraceutical applications.

In vitro assessment of the toxicity of small silver nanoparticles and silver ions to the red blood cells

This work reports the toxicity of small silver nanoparticles (nanoAg, 20 nm) and silver ions (Ag⁺) to the red blood cells with the silver concentration level of 10^-6 g/mL. Results show that red blood cells (RBCs) start hemolysis when treated by nanoAg of 1.5 × 10^-5 g/mL or Ag⁺ of 2.9 × 10^-7 g/mL. A low ATPase activity of 30% has been observed after RBCs being treated with Ag⁺ of 2.6 × 10^-7 g/mL, while the nanoAg does not obviously affect the ATPase activity. In molecular level, Ag⁺ is more toxic to the amino acid residues than nanoAg according to the change of fluorescence characteristics of hemoglobin (Hb). However, the nanoAg has been found to be more toxic than Ag⁺ to the secondary structure of Hb in terms of the loss of α-helix content.

Interactions of Bovine Serum Albumin with Anti-Cancer Compounds Using a ProteOn XPR36 Array Biosensor and Molecular Docking

The aim of the work was to determine the interactions of a set of anti-cancer compounds with bovine serum albumin (BSA) using a ProteOn XPR36 array biosensor and molecular docking studies. The results revealed that a total of six anti-cancer compounds: gallic acid, doxorubicin, acteoside, salvianolic acid B, echinacoside, and vincristine were able to reversibly bind to the immobilized BSA. The sensorgrams of these six compounds were globally fit to a Langmuir 1:1 interaction model for binding kinetics analysis. There were significant differences in their affinity for BSA, with doxorubicin, the weakest binding compound having 1000-fold less affinity than salvianolic acid B, the strongest binding compound. However, compounds with a similar KD often exhibited markedly different kinetics due to the differences in k_a and k_d. Molecular docking experiments demonstrated that acteoside was partially located within sub-domain IIA of BSA, whereas gallic acid bound to BSA deep within its sub-domain IIIA. In addition, the interactions between these compounds and BSA were dominated by hydrophobic forces and hydrogen bonds. Understanding the detailed information of these anti-cancer compounds can provide important insights into optimizing the interactions and activity of potential compounds during drug development.

Characterization of the Interaction between Gallic Acid and Lysozyme by Molecular Dynamics Simulation and Optical Spectroscopy

The binding interaction between gallic acid (GA) and lysozyme (LYS) was investigated and compared by molecular dynamics (MD) simulation and spectral techniques. The results from spectroscopy indicate that GA binds to LYS to generate a static complex. The binding constants and thermodynamic parameters were calculated. MD simulation revealed that the main driving forces for GA binding to LYS are hydrogen bonding and hydrophobic interactions. The root-mean-square deviation verified that GA and LYS bind to form a stable complex, while the root-mean-square fluctuation results showed that the stability of the GA-LYS complex at 298 K was higher than that at 310 K. The calculated free binding energies from the molecular mechanics/Poisson-Boltzmann surface area method showed that van der Waals forces and electrostatic interactions are the predominant intermolecular forces. The MD simulation was consistent with the spectral experiments. This study provides a reference for future study of the pharmacological mechanism of GA.

Spectroscopic analyses on interaction of bovine serum albumin with novel spiro[cyclopropane-pyrrolizin]

The interaction between novel spiro[cyclopropane-pyrrolizin] (NSCP) and bovine serum albumin (BSA) was analyzed by fluorescence and ultraviolet-visible (UV-Vis) spectroscopy at 298 K, 304 K and 310 K under simulative physiological conditions. The results showed that NSCP can effectively quench the intrinsic fluorescence of BSA via static quenching. The binding constants, binding sites of NSCP with BSA were calculated. Hydrogen binds and van der Waals force played a major role in stabilizing the complex and the binding reaction were spontaneous. According to the Förster non-radiation energy transfer theory, the average binding distances between NSCP and BSA were obtained. What is more, the synchronous fluorescence spectra indicated that the conformation of BSA has been changed.

Multi-spectroscopic investigation of the binding interaction of fosfomycin with bovine serum albumin

The interaction between fosfomycin (FOS) and bovine serum albumin (BSA) has been investigated effectively by multi-spectroscopic techniques under physiological pH 7.4. FOS quenched the intrinsic fluorescence of BSA via static quenching. The number of binding sites n and observed binding constant K_A were measured by the fluorescence quenching method. The thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ were calculated at different temperatures according to the van’t Hoff equation. The site of binding of FOS in the protein was proposed to be Sudlow’s site I based on displacement experiments using site markers viz. warfarin, ibuprofen and digitoxin. The distance r between the donor (BSA) and acceptor (FOS) molecules was obtained according to the Förster theory. The effect of FOS on the conformation of BSA was analyzed using synchronous fluorescence spectra (SFS), circular dichroism (CD) and 3D fluorescence spectra. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.

Interaction of digestive enzymes with tunable light emitting quantum dots: a thorough Spectroscopic investigation

In this article, we have examined the direct spectroscopic and microscopic evidence of efficient quantum dots-α-chymotrypsin (ChT) interaction. The intrinsic fluorescence of digestive enzyme is reduced in the presence of quantum dots through ground-state complex formation. Based on the fluorescence data, quenching rate constant, binding constant, and number of binding sites are calculated under optimized experimental conditions. Interestingly, fluorescence quenching method clearly illustrated the size dependent interaction of MPA-CdTe quantum dots. Conformational change of ChT was traced using synchronous fluorescence measurements, circular dichroism and FTIR spectroscopic methods. Furthermore, the AFM results revealed that the individual enzyme molecule dimensions were changed after interacting with quantum dot. Consequently, this result could be helpful for constructing safe and effective utilisation of QDs in biological applications.

Mechanistic and conformational studies on the interaction of a platinum(II) complex containing an antiepileptic drug, levetiracetam, with bovine serum albumin by optical spectroscopic techniques in aqueous solution

Fluorescence spectroscopy in combination with circular dichroism (CD) and ultraviolet-visible (UV-vis) absorption spectroscopy were employed to investigate the binding of a new platinum(II) complex containing an antiepileptic drug "Levetiracetam" to bovine serum albumin (BSA) under the physiological conditions. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by Pt(II) complex is a result of the formation of Pt(II) complex-BSA complex. The thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures (283, 298, and 310 K) were calculated, and the negative value for ΔH and ΔS indicate that the hydrogen bonds and van der Waals interactions play major roles in Pt(II) complex-BSA association. Binding studies concerning the number of binding sites (n~1) and apparent binding constant K b were performed by fluorescence quenching method. The site marker competitive experiments indicated that the binding of Pt(II) complex to BSA primarily took place in site II. Based on the Förster's theory, the average binding distance between Pt(II) complex and BSA was obtained (r = 5.29 nm). Furthermore, UV-vis, CD, and synchronous fluorescence spectrum were used to investigate the structural change of BSA molecules with addition of Pt(II) complex. These results indicate that the binding of Pt(II) complex to BSA causes apparent change in the secondary structure of BSA and do affect the microenvironment around the tryptophan residue.

Investigation of the effects of Zn2+, Ca2+ and Na+ ions on the interaction between zonisamide and human serum albumin (HSA) by spectroscopic methods

In this work, The effect of three metal ions Zn(2+), Ca(2+) and Na(1+) on the interaction between human serum albumin (HSA) and zonisamide (ZNS) was investigated employing fluorescence, ultraviolet-visible (UV-Vis) absorption and circular dichroism (CD) under simulated physiological conditions. Fluorescence spectroscopy revealed that these metallic ions and ZNS can quench the HSA fluorescence, and this quenching effect became more significant when both ion and drug are present together. It was found that the quenching mechanism is a combination of static quenching with nonradiative energy transfer. The binding sites number (n), the binding constant (Kb) and the spatial-distance (r) of ZNS with HSA without or with Zn(2+), Ca(2+) and Na(1+) ions were calculated. The presence of Ca(2+) and Na(+) ions decreased the binding constants (Kb) and the number of binding sites (n) of ZNS-HSA complex. However, the presence of Zn(2+) increased the affinity of ZNS for HSA largely. Changes in UV-Vis absorption and CD data are due to the microenvironment of amide moieties in HSA molecules.

The investigation of the interaction between Tropicamide and bovine serum albumin by spectroscopic methods

The fluorescence and ultraviolet-visible (UV-Vis) spectroscopy were explored to study the interaction between Tropicamide (TA) and bovine serum albumin (BSA) at three different temperatures (292, 301 and 310K) under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between TA and BSA was static quenching procedure. The binding constant (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at different temperatures. The results revealed that the binding process is spontaneous, hydrogen binds and vander Waals were the main force to stabilize the complex. According to Förster non-radiation energy transfer theory, the binding distance between TA and BSA was calculated to be 4.90 nm. Synchronous fluorescence spectroscopy indicated the conformation of BSA changed in the presence of TA. Furthermore, the effect of some common metal ions (Mg(2+), Ca(2+), Cu(2+), and Ni(2+)) on the binding constants between TA and BSA were examined.

Spectroscopic studies on the interaction between tetrandrine and two serum albumins by chemometrics methods

The binding interactions of tetrandrine (TETD) with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated by spectroscopic methods. These experimental data were further analyzed using multivariate curve resolution-alternating least squares (MCR-ALS) method, and the concentration profiles and pure spectra for three species (BSA/HSA, TETD and TETD-BSA/HSA) existed in the interaction procedure, as well as, the apparent equilibrium constants Kapp were evaluated. The binding sites number n and the binding constants K were obtained at various temperatures. The binding distance between TETD and BSA/HSA was 1.455/1.451nm. The site markers competitive experiments indicated that TETD primarily bound to the tryptophan residue of BSA/HSA within site I. The thermodynamic parameters (ΔG, ΔH and ΔS) calculated on the basis of different temperatures revealed that the binding of TETD-BSA was mainly depended on the hydrophobic interaction strongly and electrostatic interaction, and yet the binding of TETD-HSA was strongly relied on the hydrophobic interaction. The results of synchronous fluorescence, 3D fluorescence and FT-IR spectra show that the conformation of proteins has altered in the presence of TETD. In addition, the effect of some common ions on the binding constants between TETD and proteins were also discussed.

Study on the binding of chloroamphenicol with bovine serum albumin by fluorescence and UV-vis spectroscopy

The binding of chloroamphenicol (CPC) to bovine serum albumin (BSA) at 296 K, 303 K, and 310 K by fluorescence and UV-visible absorption spectroscopy were investigated under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between CPC and BSA was combined quenching (dynamic and static quenching) procedure at low CPC concentration, or a dynamic quenching procedure at high concentrations. The binding constants, binding sites and the corresponding thermodynamic parameters of the interaction system were calculated. According to Förster non-radiation energy transfer theory, the binding distance between CPC and BSA was calculated to be 3.02 nm. Both synchronous fluorescence and FT-IR spectra confirmed the interaction, and indicated the conformational changes of BSA. The effects of some common metal ions Ca(2+), Ni(2+), Mg(2+), Fe(2+), and Cu(2+) on the binding constant between CPC and BSA were examined. Furthermore, we investigated the possible sub-domains on BSA that bind CPC by displacement experiments.

Investigation of the interaction between indigotin and two serum albumins by spectroscopic approaches

The binding characteristics of indigotin with human serum albumin (HSA) and bovine serum albumin (BSA) have been investigated by various spectroscopic techniques. Spectroscopic analysis revealed that the quenching mechanism between indigotin and HSA/BSA belonged to the static quenching. The displacement experiments suggested that indigotin primarily bound to tryptophan residues on proteins within site I. The thermodynamic parameters indicated that the binding of indigotin–HSA/BSA mainly depended on the hydrophobic interaction. The binding distance of indigotin to HSA/BSA was evaluated. The results by synchronous fluorescence, three-dimensional fluorescence, Fourier Transform Infrared spectroscopy (FT-IR) and circular dichroism (CD) spectra showed that the conformation of proteins altered in the presence of indigotin.

Molecular spectroscopic on interaction between Methyl hesperidin and Buman serum albumin

The interaction of Methyl hesperidin (MH) with Buman serum albumin was studied by spectroscopic methods including Fluorescence quenching technology, UV absorbance spectra and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. The result of fluorescence titration revealed that Methyl hesperidin could quench the intrinsic fluorescence of BSA and the quenching mechanism should be a combined quenching process. The binding constants at three temperatures (296, 303, and 310 K) were 1.82, 2.69, and 3.4 × 10(4)L mol(-1), respectively. The distance between donor (BSA) and acceptor (MH) was 5.54 nm according to the Förster theory of non-radiation energy transfer. In addition, FT-IR spectroscopy showed that the binding of MH to BSA changed the secondary structure of protein.

Studies on interaction between an imidazole derivative and bovine serum by spectral methods

The interaction between a trifluoromethyl substituted imidazole derivative 2-(4-(trifluoromethyl)phenyl)-1-phenyl-1H-imidazo[4,5-f] [1,10] phenanthroline (tfmppip) and bovine serum albumin (BSA) was investigated by solution spectral studies. The observed experimental result shows that the imidazole derivative has strong ability to quench the fluorescence of BSA by forming complex which is stabilized by electrostatic interactions. The effective quenching constants (k(sv)) were 2.79 × 10(4), 2.51 × 10(4), and 2.32 × 10(4) at 301, 310 and 318K respectively. The Stern-Volmer quenching constant (K(sv)), binding site number (n), apparent binding constant (K(A)) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were calculated. The distance between the donor (BSA) and acceptor (tfmppip) was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence technique. The effect of metal ions such as Cu(2+), Zn(2+), Ca(2+), Mg(2+), Ni(2+), Co(2+) and Fe(2+) on the binding constants between the imidazole derivative and BSA were also studied.

Binding interaction of 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole with bovine serum albumin

A promising benzimidazole derivative 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole (MBTBI) has been synthesized and characterized by single crystal XRD, NMR, mass and IR spectral techniques. The mutual interaction of this benzimidazole derivative (MBTBI) with bovine serum albumin (BSA) was investigated using solution spectral studies. The fluorescence quenching mechanism of BSA by MBTBI was analyzed and the binding constant has been calculated. The binding distance between these two was obtained based on the theory of Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant was also examined.

Interaction of tetramethylpyrazine with two serum albumins by a hybrid spectroscopic method

The interactions of tetramethylpyrazine (TMPZ) with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated by various spectroscopic techniques. Fluorescence tests showed that TMPZ could bind to BSA/HSA to form complexes. The binding constants of TMPZ-BSA and TMPZ-HSA complexes were observed to be 1.442 × 10(4) and 3.302 × 10(4)M(-1) at 298K, respectively. The thermodynamic parameters (ΔG, ΔH and ΔS) calculated on the basis of different temperatures revealed that the binding of TMPZ-HSA was mainly depended on hydrophobic interaction, and yet the binding of TMPZ-BSA might involve hydrophobic interaction strongly and electrostatic interaction. The results of synchronous fluorescence, three-dimensional fluorescence, UV-vis absorption, FT-IR and CD spectra showed that the conformations of both BSA and HSA altered with the addition of TMPZ. The binding average distance between TMPZ and BSA/HSA was evaluated according to Föster non-radioactive energy transfer theory. In addition, with the aid of site markers (such as, phenylbutazone, ibuprofen and digitoxin), TMPZ primarily bound to tryptophan residues of BSA/HSA within site I (sub-domain II A).

Two new dicopper(II) complexes with oxamido-bridged ligand: synthesis, crystal structures, DNA binding/cleavage and BSA binding activity

New oxamido-bridged copper(II) complexes, [Cu(2)(oxbp)(H(2)O)(2)(NCS)(2)] (1) and [Cu(2)(oxbp)(μ-DMSO)(2)(NCS)(2)][Cu(2)(oxbp)(DMSO)(2)(NCS)(2)] (2) (H(2)oxbp=N,N'-bis(2-(diethylamino)ethyl)oxalamide), were synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR, and electronic spectra. X-ray analysis revealed that complex 1 consists of neutral binuclear [Cu(2)(oxbp)(H(2)O)(2)(NCS)(2)] units which forms a two-dimensional network through intermolecular hydrogen bonds and complex 2 is constructed by neutral [Cu(2)(oxbp)(μ-DMSO)(2)(NCS)(2)] (2a) and [Cu(2)(oxbp)(DMSO)(2)(NCS)(2)] (2b) entities which alternately distribute to form a two-dimensional network by means of quasi μ-DMSO bridge and intermolecular hydrogen bonds. In both 1 and 2, bicopper centers are linked by the "trans-form" oxamido bridges with the distances of 5.272 Å for 1 and av. 5.296 Å for 2, respectively. The interaction of Cu(II) complexes with DNA was investigated by UV-visible, fluorescence emission spectrometry and agarose gel electrophoresis. The apparent binding constant (K(app)) values of 3.16×10(5) M(-1) for 1 and 4.9×10(5) M(-1) for 2 suggest moderate intercalative binding modes between the complexes and DNA. Complex 1 displayed efficient oxidative cleavage of supercoiled DNA, which might indicate that the underlying mechanism involves singlet oxygen (((1))O(2)) as reactive oxygen species. Complex 2 is characteristic of the involvement of a singlet oxygen-like entity and hydrogen peroxide in the cleavage process. In addition, our present work showed, by fluorescence spectrometry of BSA with complexes, both 1 and 2 bind to BSA with a medium affinity through a static mode which is tentatively assigned binding to Trp134 in BSA.

Luminescent study on the binding interaction of bioactive imidazole with bovine serum albumin-A static quenching mechanism

Novel bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. The interaction between the imidazole derivative and bovine serum albumin (BSA) was investigated by fluorescence and UV-vis absorption spectroscopy. The fluorescence quenching of BSA by the imidazole derivatives may be due to the formation of imidazole-BSA complex. The fluorescence quenching mechanism of BSA by imidazole was analyzed and the binding constant has been calculated. The binding distance between imidazole and BSA was obtained based on Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant between imidazole and BSA was also examined.

Binding interaction of bioactive imidazole with bovine serum albumin--a mechanistic investigation

A novel Y-shaped imidazole derivative 4-((E)-2-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)vinyl)phenol has been synthesized and characterised by IR, UV-vis, mass and NMR spectral techniques. The mutual interaction of this imidazole derivative (DPTIV) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by DPTIV was analyzed and the binding constant has been calculated. The binding distance between DPTIV and BSA was obtained based on the theory of Forester's non-radiation energy transfer. The effect of some common ions on the binding constant between DPTIV and BSA was also examined.

Study on the interaction between thiazolopyrimidine analogues and bovine serum albumin

Fluorescence and ultraviolet spectroscopy were used to explore the interaction between thiazolopyrimidines (TAPM) and bovine serum albumin (BSA) under imitated physiological conditions. The experimental results show that thiazolopyrimidines can quench the fluorescence of BSA through a static quenching process. The binding constants, binding sites, and thermodynamic parameters at different temperatures were calculated. The calculated results indicate that the interaction between thiazolopyrimidines and BSA is driven mainly by Van der Waals' force and hydrogen bonds. The binding distances r was obtained based on Förster theory of non-radiation energy transfer. The comparison of binding potency of thiazolopyrimidines and BSA suggests that the substituent on the benzene ring promotes the binding process of thiazolopyrimidines and BSA.

Study on the interaction between salvianic acid A sodium and bovine serum albumin by spectroscopic methods

The interaction between salvianic acid A sodium (SAS) and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopy at different temperatures under imitated physiological conditions. The experimental results showed that the fluorescence of BSA was quenched by SAS through a static quenching procedure. The binding constants of SAS with BSA were 2.03, 1.17 and 0.71×10(5) L mol(-1) at 291, 298 and 305 K, respectively. Negative values of ΔG, ΔH, and ΔS indicate that the interaction between SAS and BSA is driven by hydrogen bonds and van der Waals forces. According to Förster non-radiation energy transfer theory, the binding distance between BSA and SAS was calculated to be about 2.92 nm. The effect of SAS on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effect of some metal ions Cu(2+), Ca(2+), Mg(2+), and Zn(2+) on the binding constant between SAS and BSA was examined.

Rational approach to select small peptide molecular probes labeled with fluorescent cyanine dyes for in vivo optical imaging

We demonstrate that the structure of carbocyanine dyes, which are commonly used to label small peptides for molecular imaging and not the bound peptide, controls the rate of extravasation from blood vessels to tissue. By examining several near-infrared (NIR) carbocyanine fluorophores, we demonstrate a quantitative correlation between the binding of a dye to albumin, a model plasma protein, and the rate of extravasation of the probe into tissue. Binding of the dyes was measured by fluorescence quenching of the tryptophans in albumin and was found to be inversely proportional to the rate of extravasation. The rate of extravasation, determined by kurtosis from longitudinal imaging studies using rodent ear models, provided a basis for quantitative measurements. Structure-activity studies aimed at evaluating a representative library of NIR fluorescent cyanine probes showed that hydrophilic dyes with binding constants several orders of magnitude lower than their hydrophobic counterparts have much faster extravasation rate, establishing a foundation for rational probe design. The correlation provides a guideline for dye selection in optical imaging and a method to verify if a certain dye is optimal for a specific molecular imaging application.

Interaction of alpinetin with bovine serum albumin: Probing of the mechanism and binding site by spectroscopic methods

The binding interaction between alpinetin and bovine serum albumin (BSA) in physiological buffer solution (pH 7.4) was investigated by fluorescence, UV-vis spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. It was proved from fluorescence spectra that the fluorescence quenching of BSA by alpinetin was probably a result of the formation of BSA-alpinetin complexes, and the binding constant (K(a)) were determined according to the modified Stern-Volmer equation. The thermodynamic parameters, enthalpy change (DeltaH) and entropy change (DeltaS), were calculated to be 22.10kJmol(-1) and 166.04Jmol(-1)K(-1), respectively, which indicated that the interaction between alpinetin and BSA was driven mainly by hydrophobic interaction. Moreover, the competitive experiments of site markers suggested that the binding site of alpinetin to BSA was located in the region of subdomain IIA (sudlow site I). The binding distance (r) between the donor (BSA) and the acceptor (alpinetin) was 3.32nm based on the Förster theory of non-radioactive energy transfer. In addition, the results of synchronous fluorescence and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of alpinetin.