Competition of cytarabine and aspirin in binding to serum albumin in multidrug therapy

The aim of this study was to describe a competition between cytarabine (araC) and aspirin (ASA) in binding with bovine serum albumin (BSA). High-affinity binding sites for both drugs were determined using a spectrofluorimetric method. Cytarabine as well as aspirin binds in the IIA hydrophobic subdomain of the transporting protein. Binding constants for araC-BSA and ASA-BSA were calculated by the Scatchard method. Analysis of ultraviolet (UV) difference spectra showed that araC, which has a higher affinity to BSA in comparison to ASA [Ka(araC) > Ka(ASA)] displaces ASA in high-affinity binding sites.The competition between drugs in low-affinity binding sites was investigated using (1)H nuclear magnetic resonance (NMR) and 13C-NMR spectra. We concluded that in the low-affinity binding sites cytarabine decreases the affinity of albumin toward aspirin. However, the interaction between araC and BSA becomes more difficult in the presence of aspirin.     

Competitive binding of anticancer drugs 5-fluorouracil and cyclophosphamide with serum albumin: Calorimetric insights

BackgroundIsothermal titration calorimetry (ITC) has emerged as an excellent method to characterize drug–protein interactions. 5-Fluorouracil and cyclophosphamide have been used in combination for the treatment of breast carcinoma, though individually these drugs have also been useful in treating other types of cancer. A quantitative understanding of binding of these drugs with the transport protein under different conditions is essential for optimizing recognition by the protein and delivery at the target.MethodsThe values of binding constant, enthalpy, and entropy of binding have been determined by using ITC. Fluorescence and circular dichroism spectroscopies have been used to obtain further support to calorimetric observations, monitor conformational changes in the protein and establishing stoichiometry of association.ResultsThe thermodynamic parameters have enabled a quantitative understanding of the affinity of 5-fluorouracil and cyclophosphamide with bovine serum albumin. The nature of binding has been unraveled based on effect of ionic strength, tetrabutyl-ammonium bromide, and sucrose which interfere in ionic, hydrophobic, and hydrogen bonding interactions. The binding site has been identified by using site marker warfarin in combination with 5-fluorouracil and cyclophosphamide. Further, the experiments have been done to establish whether both the drugs share the same binding site, and the effect of antibiotic drug carbenecillin and anti-inflammatory drug naproxen on their association.General significanceTuning optimum association of drugs with the transport vehicles for effective drug delivery requires identification of the nature of interacting groups in terms of energetics of interactions. Such studies employing ITC have direct significance in rational drug design. This article is part of a Special Issue entitled Microcalorimetry in the BioSciences — Principles and Applications, edited by Fadi Bou-Abdallah.     

On the contemporaneous, reversible interaction of different ligands with serum albumins in dilute aqueous solutions: Fluorescein and phenylbutazone

The binding affinity of fluorescein and of phenylbutazone to human serum albumin (HSA) and to bovine serum albumin (BSA), respectively, as well as of the two drugs together to each protein in dilute aqueous solution has been studied by means of gel permeation chromatography, circular dichroism, U.V. absorption and fluorescence spectroscopy. Identity of and/or interdependence between primary binding sites for the two ligands considered on HSA and BSA are evidenced and correlated with a simple theoretical approach to mixed drugs binding.     

Interactions of very long-chain saturated fatty acids with serum albumin

The remarkable binding properties of serum albumin have been investigated extensively, but little is known about an important class of fatty acids, the very long-chain saturated fatty acids (VLCFA; >18 carbons). Although VLCFA are metabolized efficiently in normal individuals, they are markers for and possibly causative agents of several peroxisomal disorders. We studied the binding of [(13)C]carboxyl-enriched arachidic (C20:0), behenic (C22:0), lignoceric (C24:0), and hexacosanoic (C26:0) acids to bovine serum albumin (BSA) by (13)C-NMR spectroscopy. For each VLCFA, the NMR spectra showed multiple signals at chemical shifts previously identified for long-chain fatty acids (12-18 carbons), suggesting stabilization of binding by similar, if not identical, interactions of the fatty acid carboxyl anion with basic amino acid residues. The maximal binding (mol of VLCFA/mol of BSA) and the number of observed binding sites decreased with increasing chain length, from 4-5 for C20:0, 3-4 for C22:0, and 2 for C24:0; we validated our previous conclusion that BSA has only one site for C26:0 (Ho, J. K., H. Moser, Y. Kishimoto, and J. A. Hamilton. 1995. J. Clin. Invest. 96: 1455-1463). Analysis of chemical shifts suggested that the highest affinity sites for VLCFA are low affinity sites for long-chain fatty acids. In competition experiments with (13)C-labeled C22:0 (3 mol/mol of BSA) and unlabeled oleic acid, C22:0 bound to BSA in the presence of up to 4 mol of oleic acid/mol of BSA, but 1 mol was shifted into a different site. Our studies suggest that albumin has adequate binding capacity for the low plasma levels of VLCFA with 20 to 26 carbons, but the protein may not be able to bind longer chain VLCFA.     

The binding of pyridoxal 5'-phosphate to human serum albumin

Most of the pyridoxal 5'-phosphate (PLP) in plasma is bound to protein, primarily albumin. Binding to protein is probably important in transporting PLP in the circulation and in regulating its metabolism. The binding of PLP to human serum albumin (HSA) was studied using absorption spectral analysis, equilibrium dialysis, and inhibition studies. The kinetics of the changes in the spectrum of PLP when mixed with an equimolar concentration of HSA at pH 7.4 followed a model for two-step consecutive binding with rate constants of 7.72 mM-1 min-1 and 0.088 min-1. The resulting PLP-HSA complex had absorption peaks at 338 and 414 nm and was reduced by potassium borohydride. The 414-nm peak is probably due to a protonated aldimine formed between PLP and HSA. The binding of PLP to bovine serum albumin (BSA) at equimolar concentrations at pH 7.4 occurred at about 10% the rate of its binding to HSA. The final PLP-BSA complex absorbed maximally at 334 nm and did not appear to be reduced with borohydride. Equilibrium dialysis of PLP and HSA indicated that there were more than one class of binding sites of HSA for PLP. There was one high affinity site with a dissociation constant of 8.7 microM and two or more other sites with dissociation constants of 90 microM or greater. PLP binding to HSA was inhibited by pyridoxal and 4-pyridoxic acid. It was not inhibited appreciably by inorganic phosphate or phosphorylated compounds. The binding of PLP to BSA was inhibited more than its binding to HSA by several compounds containing anionic groups. It is concluded that PLP binds differently to HSA than it does to BSA.     

Characterization of covalent protein conjugates using solid-state 13C NMR spectroscopy.

Cross-polarization magic-angle spinning (CPMAS) 13C NMR spectroscopy has been used to characterize covalent conjugates of alachlor, an alpha-chloroacetamide hapten, with glutathione (GSH) and bovine serum albumin (BSA). The solid-state NMR method demonstrates definitively the covalent nature of these conjugates and can also be used to characterize the sites of hapten attachment to proteins. Three different sites of alachlor binding are observed in the BSA system. Accurate quantitation of the amount of hapten covalently bound to GSH and BSA is reported. The solid-state 13C NMR technique can easily be generalized to study other small molecule/protein conjugates and can be used to assist the development and refinement of synthetic methods needed for the successful formation of such protein alkylation products.     

Investigation on the site-selective binding of bovine serum albumin by erlotinib hydrochloride

The purpose of this study was to investigate the site-selective binding of erlotinib hydrochloride (ET), a targeted anticancer drug, to bovine serum albumin (BSA) through 1H NMR, spectroscopic, thermodynamic, and molecular modeling methods. The fluorescence quenching of BSA by ET was a result of the formation of BSA–ET complex with high binding affinity. The site marker competition study combined with isothermal titration calorimetry experiment revealed that ET binds to site II of BSA mainly through hydrogen bond and van der Waals force. Molecular docking was further applied to define the specific binding site of ET to BSA. The conformation of BSA was changed in the presence of ET, revealed by synchronous fluorescence, circular dichroism, and three-dimensional fluorescence spectroscopy results. Further, NMR analysis of the complex revealed that the binding capacity contributed by the aromatic protons in the binding site of BSA might be greater than the aliphatic protons.

An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:26     

Binding of pyridoxal 5'-phosphate to bovine serum albumin and albumin fragments obtained after proteolytic hydrolysis. Localization and nature of the primary PLP binding site.

The binding of pyridoxal 5'-phosphate (PLP) to bovine serum albumin (BSA), and to large BSA fragments obtained after proteolytic hydrolysis, was investigated in order to study the structure of these fragments in relation to the albumin structure itself, and to get information about the PLP binding sites on albumin. From absorbance and circular dichroism spectra, combined with peptide mapping of the tryptic digests of the reduced PLP-protein complexes, it could be concluded that the primary binding site is localized with the NH2-terminal part of the albumin molecule. The COOH-terminal part contains one or more secondary sites. It appeared that in albumin and in the largest NH2-terminal fragment, the environment of the primary binding site is rather apolar in character. However, in the smallest NH2-terminal fragment this site is more exposed to the solvent. This suggests that the part of the peptide chain which is not common in both fragments has a stabilizing effect on the structure around the primary binding site.     

Protein adsorption at solid-liquid interfaces: Part II--Adsorption from binary protein mixture

Extent of adsorption of proteins at alumina-water interface from solutions containing binary mixture of beta-lactoglobulin and bovine serum albumin (BSA), beta-lactoglobulin and gelatin, and gelatin and bovine serum albumin has been estimated as functions of protein concentrations at varying pH, ionic strength, temperature and weight fraction ratios of protein mixture. The extent of adsorption (gamma lacw) of lactoglobulin in the presence of BSA increases with increase of protein concentration (Clac) until it reaches a maximum but a fixed value gamma lacw(m). Extent of adsorption gamma serw also initially increases with increase of protein concentrations until it reaches maximum value gamma serw(m). Beyond these protein concentrations, adsorbed BSA is gradually desorbed due to the preferential adsorption of lactoglobulin from the protein mixture. In many systems, gamma serw at high protein concentrations even becomes negative due to the strong competition of BSA and water for binding to the surface sites in the presence of lactoglobulin. For lactoglobulin-gelatin mixtures, adsorption of both proteins is enhanced as protein concentration is increased until limiting values for adsorption are reached. Beyond the limiting value, lactoglobulin is further accumulated at the interface without limit when protein concentration is high. For gelatin-albumin mixtures, extent of gelatin adsorption increases with increase in the adsorption of BSA. The limit for saturation of adsorption for gelatin is not reached for many systems. At acid pH, adsorbed BSA appears to be desorbed from the surface in the presence of gelatin. From the results thus obtained the role of electrostatic and hydrophobic effects in controlling the adsorption process has been analysed.     

Interaction of piroxicam with bovine serum albumin investigated by spectroscopic,calorimetric and computational molecular methods

Abstract

The binding of drugs to serum proteins is governed by weak non-covalent forces. In this study, the nature and magnitude of the interactions between piroxicam (PRX) and bovine serum albumin (BSA) was assessed using spectroscopic, calorimetric and computational molecular methods. The fluorescence data revealed an atypical behavior during PRX and BSA interaction. The quenching process of tryptophan (Trp) by PRX is a dual one (approximately equal static and dynamic quenched components). The FRET results indicate that a non-radiative transfer of energy occurred. The association constant and the number of binding sites indicate moderate PRX and BSA binding. The competitive binding study indicates that PRX is bound to site I from the hydrophobic pocket of subdomain IIA of BSA. The synchronous spectra showed that the microenvironment around the BSA fluorophores and protein conformation do not change considerably. The Trp lifetimes revealed that PRX mainly quenches the fluorescence of Trp-213 situated in the hydrophobic domain. The CD and DSC investigation show that addition of PRX stabilizes the protein structure. ITC results revealed that BSA-PRX binding involves a combination of electrostatic, hydrophobic and hydrogen interactions. The analysis of the computational data is consistent with the experimental results. This thorough investigation of the PRX-BSA binding may provide support for other studies concerning moderate affinity drugs with serum protein.

Communicated by Ramaswamy H. Sarma     

Elucidating the Influence of Gold Nanoparticles on the Binding of Salvianolic Acid B and Rosmarinic Acid to Bovine Serum Albumin

Salvianolic acid B and rosmarinic acid are two main water-soluble active ingredients from Salvia miltiorrhiza with important pharmacological activities and clinical applications. The interactions between salvianolic acid B (or rosmarinic acid) and bovine serum albumin (BSA) in the presence and absence of gold nanoparticles (Au NPs) with three different sizes were investigated by using biophysical methods for the first time. Experimental results proved that two components quenched the fluorescence of BSA mainly through a static mechanism irrespective of the absence or presence of Au NPs. The presence of Au NPs decreased the binding constants of salvianolic acid B with BSA from 27.82% to 10.08%, while Au NPs increased the affinities of rosmarinic acid for BSA from 0.4% to 14.32%. The conformational change of BSA in the presence of Au NPs (caused by a noncompetitive binding between Au NPs and drugs at different albumin sites) induced changeable affinity and binding distance between drugs and BSA compared with no Au NPs. The competitive experiments revealed that the site I (subdomain IIA) of BSA was the primary binding site for salvianolic acid B and rosmarinic acid. Additionally, two compounds may induce conformational and micro-environmental changes of BSA. The results would provide valuable binding information between salvianolic acid B (or rosmarinic acid) and BSA, and also indicated that the Au NPs could alter the interaction mechanism and binding capability of drugs to BSA, which might be beneficial to understanding the pharmacokinetics and biological activities of the two drugs.     

Analysis of Binding Interaction of Curcumin and Diacetylcurcumin with Human and Bovine Serum Albumin Using Fluorescence and Circular Dichroism Spectroscopy

The current study reports the binding of curcumin (CUR) as the main pharmacologically active ingredient of turmeric and diacetylcurcumin (DAC) as a bioactive derivative of curcumin to human serum albumin (HSA) and bovine serum albumin (BSA). The apparent binding constants and number of substantive binding sites have been evaluated by fluorescence quenching method. The distance (r) between donor (HSA and BSA) and acceptor (CUR and DAC) was obtained on the basis of the Förster’s theory of non-radiative energy transfer. The minor changes on the far-UV circular dichroism spectra resulted in partial changes in the calculated secondary structure contents of HSA and BSA. The negligible alteration in the secondary structure of both albumin proteins indicated that ligand-induced conformational changes are localized to the binding site and do not involve considerable changes in protein folding. The visible CD spectra indicated that the optical activity observed during the ligand binding due to induced-protein chirality. All of the achieved results suggested the important role of the phenolic OH group of CUR in the binding process.     

Investigations of interaction mechanism and conformational variation of serum albumin affected by artemisinin and dihydroartemisinin

In this work, binding interactions of artemisinin (ART) and dihydroartemisinin (DHA) with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated thoroughly to illustrate the conformational variation of serum albumin. Experimental results indicated that ART and DHA bound strongly with the site I of serum albumins via hydrogen bond (H-bond) and van der Waals force and subsequently statically quenched the intrinsic fluorescence of serum albumins through concentration-dependent manner. The quenching abilities of two drugs on the intrinsic fluorescence of HSA were much higher than the quenching abilities of two drugs on the intrinsic fluorescence of BSA. Both ART and DHA, especially DHA, caused the conformational variation of serum albumins and reduced the α-helix structure content of serum albumins. DHA with hydrophilic hydroxyl group bound with HSA more strongly, suggesting the important roles of the chemical polarity and the hydrophilicity during the binding interactions of two drugs with serum albumins. These results reveal the molecular understanding of binding interactions between ART derivatives and serum albumins, providing vital information for the future application of ART derivatives in biological and clinical areas.     

Structural investigations of stereoselective profen binding by equine and leporine serum albumins

Serum albumin, the most abundant transport protein of mammalian blood, interacts with various nonsteroidal anti-inflammatory drugs (NSAIDs) affecting their disposition, metabolism, and excretion. A big group of chiral NSAIDs transported by albumin, profens, is created by derivatives of 2-arylpropionic acid. The chiral center in the structures of profens is adjacent to the carboxylate moiety and often determines different pharmacological properties of profen enantiomers. This study describes crystal structures of two albumins, isolated from equine and leporine serum, in complexes with three profens: ibuprofen, ketoprofen, and suprofen. Based on three-dimensional structures, the stereoselectivity of albumin is discussed and referred to the previously published albumin complexes with drugs. Drug Site 2 (DS2) of albumin, the bulky hydrophobic pocket of subdomain IIIA with a patch of polar residues, preferentially binds (S)-enantiomers of all investigated profens. Almost identical binding mode of all these drugs clearly indicates the stereoselectivity of DS2 towards (S)-profens in different albumin species. Also, the affinity studies show that DS2 is the major site that presents high affinity towards investigated drugs. Additionally, crystallographic data reveal the secondary binding sites of ketoprofen in leporine serum albumin and ibuprofen in equine serum albumin, both overlapping with previously identified naproxen binding sites: the cleft formed between subdomains IIIA and IIIB close to the fatty acid binding site 5 and the niche created between subdomains IIA and IIIA, called fatty acid site 6.     

Characterization of spin-labelled fatty acids and hematoporphyrin binding sites interactions in serum albumin

Electron paramagnetic resonance (EPR) was used to investigate the spin-labelled fatty acid (SLFA) binding equilibrium to human (HSA) and bovine (BSA) serum albumin. The number of 5-doxyl stearate (5-DS) and 16-doxyl stearate (16-DS) binding sites on HSA and BSA were found to be equal, while the association constants, KA values (especially those of the primary binding site) were different. The applied EPR spectra analysis permitting a quantitative distinguishing between slow macromolecular rotation (pi c) and fast anisotropic motion (steric restriction, S) of bound SLFA, allowed SLFA oxazolidinyl ring mobility to be estimated. The 5-DS nitroxide radical is completely immobilized within the HSA protein matrix (S approximately 1.0, pi c approximately 56 +/- 1 ns). The 5-DS when bound to BSA exhibited the presence of more extensive fluctuations (lower S and pi c values) and its immersion depth with respect to BSA surface was calculated to be 4 +/- 2 A. The 16-DS oxazolidinyl radical bound to HSA was found to undergo moderated fluctuations (both S and pi c are smaller with respect to 5-DS) and it is buried deeper within the protein core (rimm = 10 +/- 2 A with respect to BSA surface). The tetrapyrrole ligands hematoporphyrin (Hp) and hematoporphyrin derivative (HpD) were found to induce well detectable changes in the SLFA binding patterns to serum albumin. The action mode was determined to be different for 16-DS (primary) and 5-DS (secondary) serum albumin binding sites: (i) 5-DS is extruded from several binding sites accompanied by an increase in KA in the remaining ones; (ii) simultaneous binding of 16-DS and Hp consists of cooperative and non-cooperative phases (both the number of the independent sites and the parameter of cooperativity, alpha, being dependent on Hp/HSA ratio); (iii) in principal the mobilities of 5-DS and 16-DS bound to HSA are changed, depending on the porphyrin/HSA ratio; and (iv) the effective immersion depth of the paramagnetic centres with respect to the protein surface is increased when Hp is present as a second ligand (rimm = 7 +/- 2 and 16 +/- 2 A for 5-DS and 16-DS, respectively).     

Biophysical insights into the binding characteristics of bovine serum albumin with dipyridamole and the influence of molecular interaction with β cyclodextrin

Abstract

The binding characteristic of anti-platelet drug dipyridamole has been investigated with a transport protein, serum albumin. A multi-spectroscopic approach has been employed, and the results were well supported by in silico molecular docking and simulation studies. The fluorescence quenching of serum albumin at three different temperatures revealed that the mechanism involved is static and the binding constant of the interaction was found to be of the order of 10⁴ M^?1. The reaction was found to be spontaneous and involved hydrophobic interactions. Synchronous, 3D fluorescence and CD spectroscopy indicated a change in conformation of bovine serum albumin (BSA) on interaction with DP. Using site-selective markers, the binding site of DP was found to be in subdomain IB. Molecular docking studies further corroborated these results. Molecular dynamic (MD) simulations showed lower RMSD values on interaction, suggesting the existence of a stable complex between DP and BSA. Furthermore, since β-Cyclodextrin (βCD) is used to improve the solubility of DP in ophthalmic solutions, therefore, the effect of (βCD) on the interaction of BSA and DP was also studied, and it was found that in the presence of βCD, the binding constant for BSA-DP interaction decreased. The present study is an attempt to characterize the transport of DP and to improve its bioavailability, consequently helping in dosage design to achieve optimum therapeutic levels.

Communicated by Ramaswamy H. Sarma     

Magnetic core/shell Fe3O4/Au nanoparticles for studies of quinolones binding to protein by fluorescence spectroscopy

Magnetic core/shell Fe₃O₄/Au nanoparticles were used in the determination of drug binding to bovine serum albumin (BSA) using a fluorescence spectroscopic method. The binding constants and number of binding sites for protein with drugs were calculated using the Scatchard equation. Because of their superparamagnetic and biocompatible characteristics, magnetic core/shell Fe₃O₄/Au nanoparticles served as carrier proteins for fixing proteins. After binding of the protein to a drug, the magnetic core/shell Fe₃O₄/Au nanoparticles–protein–drug complex was separated from the free drug using an applied magnetic field. The free drug concentration was obtained directly by fluorescence spectrometry and the proteins did not influence the drug determination. So, the achieved number of binding sites should be reliable. The binding constant and site number for ciprofloxacin (CPFX) binding to BSA were 2.055 × 10⁵ L/mol and 31.7, and the corresponding values for norfloxacin (NOR) binding to BSA were 1.383 × 10⁵ L/mol and 38.8. Based on the achieved results, a suitable method was proposed for the determination of binding constants and the site number for molecular interactions. The method was especially suitable for studies on the interactions of serum albumin with the active ingredients of Chinese medicine. Copyright © 2015 John Wiley & Sons, Ltd.     

Binding interaction of a biological photosensitizer with serum albumins: a biophysical study

A photophysical study on the binding interaction of an efficient cancer cell photosensitizer, norharmane (NHM), with model transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), has been performed using a combination of steady-state and time-resolved fluorescence techniques. The emission profile undergoes a remarkable change upon addition of the proteins to the buffered aqueous solution of the photosensitizer. The polarity-dependent prototropic transformation is responsible for the remarkable sensitivity of this biological fluorophore to the protein environments. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that the albumin proteins introduce motional restriction on the drug molecule. Light has been thrown on the denaturing action of urea on the probe-bound protein. The probable binding site of the drug in proteins has also been assessed from the combination of denaturation study, micropolarity measurement, and fluorescence resonance energy transfer (FRET) study. The present study suggests that the stability of serum albumins is enhanced upon binding with the drug.     

Characterization of colchicine binding with normal and glycated albumin: In vitro and molecular docking analysis

The transport of more than 90% of the drugs viz. anticoagulants, analgesics, and general anesthetics in the blood takes place by albumin. Hence, albumin is the prime protein needs to be investigated to find out the nature of drug binding. Serum albumin molecules are prone to glycation at elevated blood glucose levels as observed in diabetics. In this piece of work, glycation of bovine serum albumin (BSA) was carried out with glyceraldehyde and characterized by molecular docking and fluorometry techniques. Glycation of BSA showed 25% loss of free amino groups and decreased protein fluorescence (60%) with blue shift of 6 nm. The present study was also designed to evaluate the binding of colchicine (an anti-inflammatory drug) to native and glycated BSA and its ability to displace 8-analino-1-nephthalene sulfonic acid (ANS), from the BSA–ANS complex. Binding of ANS to BSA showed strong binding (K_a = 4.4 μM) with native conformation in comparison to glycated state (K_a = 8.4 μM). On the other hand, colchicine was able to quench the fluorescence of native BSA better than glycated BSA and also showed weaker affinity (K_a = 23 μM) for glycated albumin compared with native state (K_a = 16 μM). Molecular docking study showed that both glyceraldehyde and colchicine bind to common residues located near Sudlow’s site I that explain the lower binding of colchicine in the glycated BSA. Based on our results, we believe that reduced drugs-binding affinity to glycated albumin may lead to drugs accumulation and precipitation in diabetic patients.     

Study on the binding of cerium to bovine serum albumin

The interaction of Ce(3+) to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra, and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by Ce(3+) was a static quenching process, the binding constant is 6.70 × 10(5) , and the number of binding site is 1. The thermodynamic parameters (ΔH = -29.94 kJ mol(-1) , ΔG = -32.38 kJ mol(-1) , and ΔS = 8.05 J mol(-1) K(-1) ) indicate that electrostatic effect between the protein and the Ce(3+) is the main binding force. In addition, UV-vis, CD, and synchronous fluorescence results showed that the addition of Ce(3+) changed the conformation of BSA.