Showing papers on "Human serum albumin published in 2007"
TL;DR: The physiological or pathophysiological concentrations of different oxidatively modified albumin molecules vary over a wide range and are crucial in assessing the clinical relevance of altered ligand binding properties of a particularly modifiedalbumin species in various disease conditions.
Abstract: Binding and transport of a number of endogenous and exogenous compounds is an important function of the main plasma protein, albumin. In vivo and in vitro, albumin may be oxidatively modified in different ways with different agents at different sites. These modifications have various consequences on the physiological functions of albumin. Diabetes mellitus, liver diseases and nephropathy are just a few examples of disorders in which oxidative stress is involved and altered albumin functions have been described. This review is focussed on the consequences of oxidative modification on the binding properties of albumin. These range from no effect to decreased or increased binding affinities depending on the ligand under investigation and the type of modification. Indicators for modification include glycosylation, disulphide formation or the content of carbonyl groups. The redox state of albumin can affect the binding properties in several ways, including altered conformation and consequently altered affinities at binding sites and altered binding when the binding reaction itself is redox sensitive. The physiological or pathophysiological concentrations of different oxidatively modified albumin molecules vary over a wide range and are crucial in assessing the clinical relevance of altered ligand binding properties of a particularly modified albumin species in various disease conditions.
304 citations
TL;DR: A comparative study indicates that single chain diabody-albumin fusion proteins seem to be the most promising format for further studying cytotoxic activities in vitro and in vivo.
257 citations
TL;DR: A standard protocol for the preparation of doxorubicin-loaded HSA nanoparticles for further antitumoural studies was established and the anti-cancer effects of the drug-loaded nanoparticles were increased in comparison to doxorbicin solution.
256 citations
TL;DR: It is shown that more than one mechanism is involved in the interaction of nanoparticles with the brain endothelial cells and the resulting delivery of drugs to the central nervous system through the NHS-PEG-Mal 3400 linker.
239 citations
TL;DR: The results point to a partial unfolding of protein secondary structure at high ligand content in the ligand-HSA complexes.
Abstract: Crocetin (CRT) and dimethylcrocetin (DMCRT) are derived from crocins which are found in the stigmas of saffron (Crocus sativus L.), while safranal is the main component of saffron's essential oil. The aim of the present study was to examine their interaction with human serum albumin in aqueous solution at physiological conditions using constant protein concentration and various ligand contents. FT-IR and UV-visible spectroscopic methods were used to determine the ligands' binding mode, the binding constant, and the effects of ligand complexation on protein secondary structure. Structural analysis showed that crocetin, dimethylcrocetin, and safranal bind nonspecifically (H-bonding) via protein polar groups with binding constants of Kcrt =2.05 (+/-0.30) x 103 M-1, Kdmcrt = 9.60 (+/-0.35) x 104 M-1, and Ksaf = 2.11 (+/-0.35) x 103 M-1. The protein secondary structure showed no major alterations at low ligand concentrations (1 microM), whereas at higher content (1 mM), decrease of alpha-helix from 55% (free HSA) to 43-45% and increase of beta-sheet from 17% (free HSA) to 18-22% and random coil 7% (free HSA) to 10-14% occurred in the ligand-HSA complexes. The results point to a partial unfolding of protein secondary structure at high ligand content. The antioxidant activity of CRT, DMCRT, and safranal was also tested by the DPPH* antioxidant activity assay, and their IC50 values were compared to that of well-known antioxidants such as Trolox and butylated hydroxy toluene (BHT). The IC50 values of CRT and safranal were 17.8 +/- 1 microg/mL and 95 +/- 1 microg/mL, respectively, while the inhibition of DMCRT reached a point of 38.8%, which corresponds to a concentration of 40 microg/mL, and then started to decrease. The IC50 values of Trolox and BHT were 5.2 +/- 1 microg/mL and 5.3 +/- 1 microg/mL, respectively.
191 citations
TL;DR: The crystal structures of HSA-myristate in a complex of aspirin and of salicylic acid, respectively are determined and provide the structural evidence of esterase activity of H SA, and demonstrate the conformational plasticity of Hsa on drug binding.
190 citations
TL;DR: HSA structure was less perturbed by polyamine analogues compared to those of the biogenic polyamines, and the protein secondary structure showed major alterations, indicating partial protein unfolding upon polyamine interaction.
178 citations
TL;DR: The present study suggests that the stability of serum albumins is enhanced upon binding with the drug.
158 citations
TL;DR: It is postulated that BSA and HSA-FAF sequester inhibitory fatty acids released during incubations, and the apparent high Km values observed for UGT2B7 substrates arise from the presence of these endogenous inhibitors.
Abstract: Studies were performed to elucidate the mechanism responsible for the reduction in Km values of UDP-glucuronosyltransferase 2B7 (UGT2B7) substrates observed for incubations conducted in the presence of albumin. Addition of bovine serum albumin (BSA) and fatty acid-free human serum albumin (HSA-FAF), but not "crude" HSA, resulted in an approximate 90% reduction in the Km values for the glucuronidation of zidovudine (AZT) by human liver microsomes (HLM) and UGT2B7 and a 50 to 75% reduction in the S50 for 4-methylumbelliferone (4MU) glucuronidation by UGT2B7, without affecting Vmax. Oleic, linoleic, and arachidonic acids were shown to be the most abundant unsaturated long-chain fatty acids present in crude HSA and in the membranes of HLM and human embryonic kidney (HEK)293 cells, and it was demonstrated that these and other unsaturated long-chain fatty acids were UGT2B7 substrates. Glucuronides with Rf (retention factor) values corresponding to the glucuronides of linoleic and arachidonic acid were detected when HLM and HEK293 cell lysates were incubated with radiolabeled cofactor, and the intensity of the bands was modulated by the presence of crude HSA (increased) and BSA or HSA-FAF (decreased). Oleic, linoleic, and arachidonic acid inhibited AZT and 4MU glucuronidation by HLM and/or UGT2B7, due to an increase in Km/S50 without a change in Vmax. Addition of BSA and HSA-FAF reversed the inhibition. Likewise, coexpression of UGT2B7 and HSA in HEK293 cells reduced the Km/S50 values of these substrates. It is postulated that BSA and HSA-FAF sequester inhibitory fatty acids released during incubations, and the apparent high Km values observed for UGT2B7 substrates arise from the presence of these endogenous inhibitors.
148 citations
TL;DR: This strategy, which adds only a small protein domain (46 amino acids) and which utilizes high-affinity, non-covalent albumin interaction, should be broadly applicable to improve serum half-lives of small recombinant antibody molecules.
Abstract: The therapeutic application of small recombinant antibody molecules is often limited by a short serum half-life. In order to improve the pharmacokinetic properties, we have investigated a strategy utilizing fusion with an albumin-binding domain (ABD) from streptococcal protein G. This strategy was applied to a bispecific single-chain diabody (scDb CEACD3) developed for the retargeting of cytotoxic T cells to CEA-expressing tumor cells. This novel tri-functional fusion protein (scDb-ABD) was expressed in mammalian cells and recognized both antigens as well as human and mouse serum albumin. scDb-ABD was capable to retarget T cells to CEA-expressing target cells in vitro and to activate the effector cells as measured by stimulation of IL-2 release. Although activity was reduced 3-fold compared with scDb and further reduced 4-fold in the presences of human serum albumin, this assay demonstrated that scDb-ABD is active when exposed to all three antigens. Compared with scDb, the circulation time of scDb-ABD in mice was prolonged 5- to 6-fold similar to a previously described scDb-HSA fusion protein. This strategy, which adds only a small protein domain (46 amino acids) and which utilizes high-affinity, non-covalent albumin interaction, should be broadly applicable to improve serum half-lives of small recombinant antibody molecules.
146 citations
TL;DR: The amphiphilic gadolinium complex MS-325 binds to human serum albumin (HSA) in plasma resulting in an extended plasma half-life, retention of the agent within the blood compartment, and an increased relaxation rate of water protons in plasma.
Abstract: The amphiphilic gadolinium complex MS-325 ((trisodium-{(2-(R)-[(4,4-diphenylcyclohexyl) phosphonooxymethyl] diethylenetriaminepentaacetato) (aquo)gadolinium(III)}) is a contrast agent for magnetic resonance angiography (MRA) MS-325 consists of two slowly interconverting diastereoisomers, A and B (65:35 ratio), which can be isolated at pH > 85 (Tyeklar, Z; Dunham, S U; Midelfort, K; Scott, D M; Sajiki, H; Ong, K; Lauffer, R B; Caravan, P; McMurry, T J Inorg Chem 2007, 46, 6621−6631) MS-325 binds to human serum albumin (HSA) in plasma resulting in an extended plasma half-life, retention of the agent within the blood compartment, and an increased relaxation rate of water protons in plasma Under physiological conditions (37 °C, pH 74, phosphate buffered saline (PBS), 45% HSA, 005 mM complex), there is no statistical difference in HSA affinity or relaxivity between the two isomers (A 886 ± 06% bound, r1 = 420 ± 10 mM-1 s-1 at 20 MHz; B 902 ± 06% bound, r1 = 383 ± 10 mM-1 s-1 at 20
TL;DR: The synthesis of poly-aminophenylboronic acid (ABPA) imprinted beads for the recognition of the protein human serum albumin (HSA) is reported, and the resulting imprinting beads were selective for HSA.
TL;DR: The conditional stability constant at pH 7.4 for Cu(II) binding at the N-terminal site (NTS) of human serum albumin (HSA) was determined directly by competitive UV–vis spectroscopy titrations using nitrilotriacetic acid (NTA) as the competitor in 100 mM NaCl and 100-mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (Hepes
Abstract: The conditional stability constant at pH 7.4 for Cu(II) binding at the N-terminal site (NTS) of human serum albumin (HSA) was determined directly by competitive UV-vis spectroscopy titrations using nitrilotriacetic acid (NTA) as the competitor in 100 mM NaCl and 100 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (Hepes). The log Kc (NTS) value of 12.0 +/- 0.1 was determined for HSA dissolved in 100 mM NaCl. A false log log Kc (NTS) (c) value of 11.4 +/- 0.1 was obtained in the 100 mM Hepes buffer, owing to the formation of a ternary Cu(NTA)(Hepes) complex. The impact of the picomolar affinity of HSA for Cu(II) on the availability of these ions in neurodegenerative disorders is briefly discussed.
TL;DR: This paper focuses on human serum albumin (HSA), the most abundant plasma protein, proposed to serve antioxidant functions in the vascular compartment, supporting a role of HSA-Cys34 as an important redox regulator in extracellular compartments.
Abstract: Sulfenic acid (RSOH) is a central intermediate in both the reversible and irreversible redox modulation by reactive species of an increasing number of proteins involved in signal transduction and enzymatic pathways. In this paper we focus on human serum albumin (HSA), the most abundant plasma protein, proposed to serve antioxidant functions in the vascular compartment. Sulfenic acid in HSA has been previously detected using different methods after oxidation of its single free thiol Cys34 through one- or two-electron mechanisms. Since recent evidence suggests that sulfenic acid in HSA is stabilized within the protein environment, this derivative represents an appropriate model to examine protein sulfenic acid biochemistry, structure and reactivity. Sulfenic acid in HSA could be involved in mixed disufide formation, supporting a role of HSA-Cys34 as an important redox regulator in extracellular compartments.
TL;DR: Results indicate that these antibacterial peptides do bind to albumin and that this binding strongly reduces the effective concentration of peptides available to combat bacteria.
Abstract: The interactions between a range of small cationic antibacterial tripeptides and bovine and human serum albumin in a buffered aqueous solution at 25 °C have been studied using isothermal titration calorimetry. Results from the binding study indicate a single binding site on albumin with a dissociation constant between 4.3 and 22.2 μM for the different peptides. In a theoretical mouse model, a dissociation constant in this range corresponds to 95% albumin binding. The effect of this albumin interaction on the antibacterial capacity of the peptides against Staphylococcus aureus, strain ATCC 25923 was studied by including albumin in the assays at a 0.55 mM concentration. Presence of albumin induced a 10-fold increase of the minimal inhibitory concentration for the bulk of the peptides. Albumin itself has no effect on the bacterial growth and this increase is entirely ascribed to a strong competing protein binding. Collectively these results indicate that these antibacterial peptides do bind to albumin and th...
TL;DR: The results point to a partial stabilization of protein secondary structure at high retinoid content, which is the major target of several micronutrients in vivo.
TL;DR: The present work reveals a protein conformation change upon P5W30 binding, a new feature not explicitly documented in previous studies, which is a simple exothermic process, with several binding sites.
Abstract: The molecular recognition of polyoxometalates by human serum albumin is studied using two different polyoxometalates (POMs) at pH 7.5. The results are compared with those obtained at pH 3.5 and 9.0. At pH 7.5, both POMs strongly interact with the protein with different binding behaviors. The Keggin shaped POM, [H2W12O40]6- (H2W12), specifically binds the protein, forming a complex with a 1:1 stoichiometry with Ka = 2.9 × 106 M-1. The binding constant decreased dramatically with the increase of the ionic strength, thus indicating a mostly electrostatic binding process. Isothermal titration calorimetry (ITC) experiments show that the binding is an enthalpically driven exothermic process. For the wheel shaped POM [NaP5W30O110]14- (P5W30), there are up to five binding sites on the protein. Increasing the ionic strength changes the binding behavior significantly, leading to a simple exothermic process, with several binding sites. Competitive binding experiments indicate that the two POMs share one common bindi...
TL;DR: The fact that many of these glycation-related modifications are located at or near known drug binding sites on HSA explains why some differences have been previously noted in the binding of certain drugs to normal vs glycated HSA.
TL;DR: Thermodynamic analysis and molecular modeling suggest that hydrophobic interaction plays a major role in thebinding of resveratrol to HSA, and hydrogen bonding is the mainly binding force in the binding of Resveratro to Hb.
Abstract: Resveratrol is a natural phytoalexin with pharmacologic effects on several human diseases: carcinogenesis, coronary heart disease and neurodegenerative disease Due to its poor water solubility, resveratrol must be bound to proteins to keep it at a high concentration in serum In our work, the bindings of resveratrol to plasma proteins, human serum albumin (HSA) and hemoglobin (Hb), have been investigated systematically by fluorescence quenching technique, synchronous fluorescence, UV–vis absorption spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling method The fluorescence data show that the binding of resveratrol to HSA or Hb is a static quenching procedure and each protein has only one binding site for the drug The binding constant of resveratrol to HSA is larger than that of resveratrol to Hb at corresponding temperature, which indicates that the affinity of HSA toward the drug is higher than that of Hb The CD spectroscopy indicates that the secondary structures of the proteins are changed in the presence of resveratrol with the reduction of α-helices, which decreased about 1875% for HSA and 943% for Hb at the drug to proteins molar ratio of 2 Thermodynamic analysis and molecular modeling suggest that hydrophobic interaction plays a major role in the binding of resveratrol to HSA, and hydrogen bonding is the mainly binding force in the binding of resveratrol to Hb The study of molecular modeling shows that resveratrol is located in the hydrophobic cavity between subdomain IB and IIA of HSA (the entrance of site I), or located in the central cavity of Hb (partial to the subunit A)
TL;DR: The approach involves the design of a drug fragment capable of conjugating to linker molecules on a modified carrier protein via hydrazone bond formation and the proof-of-concept using recombinant human serum albumin is described.
Abstract: In order to utilize macromolecules for drug targeting and delivery, a strategy to tether organometallic ruthenium-arene drugs to carrier protein molecules was developed. The approach involves the design of a drug fragment capable of conjugating to linker molecules on a modified carrier protein via hydrazone bond formation. The proof-of-concept using recombinant human serum albumin is described.
TL;DR: The results suggest that in acute diabetes mellitus patients, HSA, after 21 days of glycation, passes through a molten globule-like state and may contribute to the pathogenesis of diabetes, and perhaps other diseases.
TL;DR: Photoirradiation at λ > 320 nm of 2-anthracenecarboxylate bound to human serum albumin in an aqueous buffer solution at 5 °C gave syn head-to-tail cyclodimer 2 in 82% ee and anti head- to-head cycloders 3 in 90% eE.
Abstract: Photoirradiation at λ > 320 nm of 2-anthracenecarboxylate bound to human serum albumin in an aqueous buffer solution at 5 °C gave syn head-to-tail cyclodimer 2 in 82% ee and anti head-to-head cyclodimer 3 in 90% ee.
TL;DR: The results confirm the important role played by conformational changes in the tertiary structure, especially in the exposure of internal hydrophobic regions that promote intermolecular interactions, and confirm that the absence of electrostatic repulsion favours the disordered non-specific interactions between molecules and consequently affects the aggregation rate.
Abstract: We report here a study on thermal aggregation of BSA at two different pH values selected to be close to the isoelectric point (pI) of this protein. Our aim is to better understand the several steps and mechanisms accompanying the aggregation process. For this purpose we have performed kinetics of integrated intensity emission of intrinsic and extrinsic dyes, tryptophans and ANS respectively, kinetics of Rayleigh scattering and of turbidity. The results confirm the important role played by conformational changes in the tertiary structure, especially in the exposure of internal hydrophobic regions that promote intermolecular interactions. We also confirm that the absence of electrostatic repulsion favours the disordered non-specific interactions between molecules and consequently affects the aggregation rate. Finally, the comparison between BSA and another relative protein, HSA, allows us to clarify the role of different domains involved in the aggregation process.
TL;DR: Binding of curcumin, an antioxidant and anti-tumor agent to human serum albumin (HSA) has been investigated by following absorption and fluorescence spectral changes in HSA andCurcumin.
TL;DR: Electronic absorption, EPR, and NMR spectroscopies indicate three specific and well-separated binding sites for CoII in HSA, where CoII ions in all three sites are in a high-spin state and coordinated in a distorted octahedral geometry.
Abstract: Human serum albumin (HSA) is the most abundant protein in the blood plasma and is involved in the transport of metal ions. Four metal-binding sites with different specificities have been described in HSA: (i) the N-terminal site provided by Asp1, Ala2, and His3, (ii) the site at the reduced Cys34, (iii) site A, including His67 as a ligand, and (iv) the nonlocalized site B. HSA can bind CoII, and HSA was proposed to be involved in CoII transport. Recently, binding of CoII to HSA has attracted much interest due to the so-called albumin cobalt binding (ACB) test approved by the Food and Drug Administration for evaluation of myocardial ischemia. Although the binding of CoII to HSA is important, the binding of CoII to HSA is not well-characterized. Here the binding of CoII to HSA was studied under anaerobic conditions to prevent CoII oxidation. Electronic absorption, EPR, and NMR spectroscopies indicate three specific and well-separated binding sites for CoII in HSA. CoII ions in all three sites are in a high...
TL;DR: A novel NMR approach based on the comparative analysis of Aβ in its inhibited and filtrated states is proposed, which reveals a mechanism for the oligomerization inhibitory function of HSA, according to which HSA targets preferentially the soluble oligomers of A β(12−28) rather than its monomeric state.
Abstract: Human serum albumin (HSA) inhibits the formation of amyloid beta-peptide (Abeta) fibrils in human plasma. However, currently it is not known how HSA affects the formation of the highly toxic soluble diffusible oligomers that occur in the initial stages of Abeta fibrillization. We have therefore investigated by solution NMR the interaction of HSA with the Abeta(12-28) peptide, which has been previously shown to provide a reliable and stable model for the early prefibrillar oligomers as well as to contain key determinants for the recognition by albumin. For this purpose we propose a novel NMR approach based on the comparative analysis of Abeta in its inhibited and filtrated states monitored through both saturation transfer difference and recently developed nonselective off-resonance relaxation experiments. This combined NMR strategy reveals a mechanism for the oligomerization inhibitory function of HSA, according to which HSA targets preferentially the soluble oligomers of Abeta(12-28) rather than its monomeric state. Specifically, HSA caps the exposed hydrophobic patches located at the growing and/or transiently exposed sites of the Abeta oligomers, thereby blocking the addition of further monomers and the growth of the prefibrillar assemblies. The proposed model has implications not only for the pharmacological treatment of Alzheimer's disease specifically but also for the inhibition of oligomerization in amyloid-related diseases in general. In addition, the proposed NMR approach is expected to be useful for the investigation of the mechanism of action of other oligomerization inhibitors as well as of other amyloidogenic systems.
TL;DR: In this article, the interaction of Apigenin and human serum albumin (HSA) had been investigated systematically by fluorescence spectroscopic, circular dichroism (CD), UV-vis absorption spectroscopy and molecular modeling.
Abstract: Apigenin (Ap) is one of the most common dietary flavonoids, and possesses extensive bioactivities. In our work, interaction of Ap and human serum albumin (HSA) had been investigated systematically by fluorescence spectroscopic, circular dichroism (CD), UV–vis absorption spectroscopic and molecular modeling. The results indicated that binding of Ap to HSA caused strong fluorescence quenching of HSA through static quenching mechanism, hydrophobic and electrostatic interaction are the predominant forces in the Ap–HSA complex, and the process of Ap binding HSA was droved by enthalpy (Δ H = −17.497 kJ mol −1 ) and entropy (Δ S = 37.04 J mol −1 ). The results from synchronous fluorescence showed that microenvironment around tyrosine (Tyr) had a slight trend (about blueshift of 1 nm) of polarity decreasing. The formation of the complex had not changed the secondary structure of HSA by CD. The binding distance r between donor (HSA) and acceptor (Ap) is 3.21 nm according to the theory of Forster resonance energy transfer. By method of molecular modeling, Ap was located to the entrance of site I by hydrophobic and electrostatic forces, which matched exactly the corresponding experimental results.
TL;DR: The results proved the mechanism of fluorescence quenching of HSA while interacting with EA is due to the formation of EA–HSA complex formation, which proves the involvement of weak interactive forces like hydrogen and hydrophobic bonds during the interaction.
Abstract: Human serum albumin (HSA) is a principal plasma protein, carries the drug molecules to target sites in human body. Ellagic acid (EA) derived from ellagitannins plays an important role as a drug because of its unique pharmacological properties. The interactions between EA and HSA were studied by fluorescence spectroscopic techniques under similar to human physiologic conditions. The binding parameters have been evaluated by fluorescence quenching methods. The results proved the mechanism of fluorescence quenching of HSA while interacting with EA is due to the formation of EA–HSA complex formation. The thermodynamic parameters like Δ H and Δ S were calculated to be −17.32 kJ/mol and 34.91 J/mol/K, respectively, which proves the involvement of weak interactive forces like hydrogen and hydrophobic bonds during the interaction. Molecular docking study shows hydrogen-bonding distance between EA and HSA molecule. The distance r between donor (HSA) and acceptor (EA) was obtained according to the Forster's theory of non-radiative energy transfer and found to be 1.96 nm. This study will give an insight on the evaluation of the drug stability during transport and releasing efficiency at the target site in human physiological conditions.
TL;DR: Circular dichroism was used to assess the structural effects of POM binding on HSA and to confirm the interaction revealed by fluorescence studies, which showed that the two POMs have different effects on the secondary structure of the protein.
Abstract: As a step toward the elucidation of the mechanistic pathways governing the known bioactivity of polyoxometalates (POMs), two representative molecules of this class of chemicals, the wheel-shaped [NaP5W30O110]14- (P5W30) and the Keggin-type anion [H2W12O40]6- (H2W12), are shown, by two independent techniques, to interact with the fatty-acid-free human serum albumin (HSA). The excited-state lifetime of the single tryptophan molecule of this protein is dramatically decreased by the binding. The quenching mechanism is found to constitute the first example of energy transfer between HSA and POMs. Such molecular recognition is believed to be a key step for subsequent evolution of the systems. Circular dichroism (CD) was used to assess the structural effects of POM binding on HSA and to confirm the interaction revealed by fluorescence studies. CD experiments showed that the two POMs have different effects on the secondary structure of the protein. Binding P5W30 partially unfolds the protein whereas H2W12 has no ...
TL;DR: In this article, the binding characteristics of human serum albumin (HSA) with phenothiazine derivatives (PDS) viz., thioridazine hydrochloride (TDH) and triflupromazine hydro chloride (TFP) have been studied by employing different spectroscopic techniques.
Abstract: In this paper, the binding characteristics of human serum albumin (HSA) with phenothiazine derivatives (PDS) viz ., thioridazine hydrochloride (TDH) and triflupromazine hydrochloride (TFP) have been studied by employing different spectroscopic techniques. The Stern–Volmer quenching constant values were found to decrease with increase in temperature thereby indicating the presence of static quenching mechanism in the interactions of PDS with HSA. The number of binding sites, n and the binding constant values, K were noticed to be 1.063 and (4.46 ± 0.040) × 10 4 L M −1 for TDH and 1.08 and (5.18 ± 0.071) × 10 4 L M −1 for TFP, respectively at 298 K. The binding distances and the energy transfer efficiency between PDS and protein were determined. The negative value of enthalpy change and positive value of entropy change in the present study indicated that both hydrogen bonding and hydrophobic forces played a major role in the binding of PDS to HSA. The circular dichroism data revealed the conformational changes in secondary structure of protein upon its interaction with PDS. The decreased binding constants of HSA–TDH/TFP in presence of common ions indicated the availability of higher concentration of free drug in plasma.