Salt-induced refolding in different domains of partially folded bovine serum albumin

The effect of chrysin binding on the conformational dynamics and unfolding pathway of human serum albumin

Studies on the interactions between ligands and proteins provide insights into how a possible medication alters the structures and activities of the target or carrier proteins. The natural flavonoid aglycone Chrysin (CHR) has demonstrated anti-inflammatory, antioxidant, antiapoptotic, neuroprotective, and antineoplastic effects, both in vitro and in vivo. In this work, we investigated the impact of CHR binding on the as-yet-unexplored conformation, dynamics, and unfolding mechanism of human serum albumin (HSA). We determined CHR binding to HSA domain-II with the association constant (Ka) of 2.70 ± 0.21 × 105 M-1. The urea-induced sequential unfolding mechanism of HSA was used to elucidate the debatable binding location of CHR. CHR binding induced both secondary and tertiary structural alterations in the protein as studied by far-UV circular dichroism and intrinsic fluorescence spectroscopy. Red edge excitation shift (REES) indicated a decrease in conformational dynamics of the protein on the complex formation. This suggested an ordered compact and spatial arrangement of the CHR-boundmolecule. The binding of CHR was found to significantly modulate the urea-induced unfolding pathway of HSA. Urea-induced unfolding pathway of HSA became a two-state process (N-U) from a three-state process (N-I-U). The interaction of CHR is found to increase the thermal stability of the protein by ∼4 °C. This study focuses on the fundamental sciences and demonstrates how prospective medication compounds can alter the dynamics and stability of protein structure.

Tracking Zone-wise perturbation during unfolding of some globular proteins using Eu(III) complex of Tetracycline as a probe exhibiting Stark splitting

Enhanced 'Antenna effect' of a suitably designed ternary complex of Eu(III), Tetracycline hydrochloride (TC) and globular proteins viz bovine serum albumin (BSA), human serum albumin (HSA) and β-lactoglobulin A (BLGA) in aqueous medium is employed to characterize the different partially unfolded states along with investigation of the micro- heterogeneous environment of the proteins during their stepwise unfolding. The zone-wise perturbation for the proteins upon denaturation by Urea and Guanidine hydrochloride (Gdn. HCl) is followed by the emission of Eu(III) through 'Antenna Effect' and that of the tryptophan (Trp) residues of the proteins as a function of denaturants both by steady state and time resolved emission study. With Gdn. HCl as denaturant, both BSA and BLGA show quenching of Eu(III) emission compared to pure protein while HSA exhibits an enhancement of antenna effect during unfolding as compared to that in its absence. In the presence of Urea, HSA and BSA show enhancement of antenna effect accompanied by Stark splitting of the ⁵D₀→⁷F₂ transition of Eu(III) although BLGA follows the similar pattern of quenching of Eu(III) emission as observed with Gdn. HCl without any Stark splitting. The proteins exhibit a two state transition with ΔG_D values of ~ 2-3 kcal mol^-1. Thus the use of Eu(III) emission as an efficient probe is advocating here to rationalize the microenvironment of the proteins during their stepwise unfolding.

Refolding of denatured gold nanoparticles-conjugated bovine serum albumin through formation of catanions between gemini surfactant and sodium dodecyl sulphate

The present work elucidates binding interactions of sodium dodecyl sulphate (SDS) with the conjugated gold nanoparticles (AuNPs)-bovine serum albumin (BSA), unfolded by each of two gemini surfactants, 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-butane (12-4-12,2Br⁻) or 1,8-bis(dodecyl-N,N-dimethylammonium bromide)-octane (12-8-12,2Br⁻). Initially, at a low concentration of SDS there is a relaxation of bioconjugates from their compressed form due to the formation of catanions between SDS and gemini surfactants. On moving towards higher concentrations of SDS, these relaxed unfolded bioconjugates renature by removal of residual bound gemini surfactants. Mixed assemblies of SDS and gemini surfactants formed during refolding of bioconjugates are characterized by DLS and FESEM measurements. A step-by-step process of refolding observed for these denatured protein bioconjugates is exactly the inverse of their unfolding phenomenon. Parameters concerning nanometal surface energy transfer (NSET) and Förster's resonance energy transfer (FRET) phenomenon were employed to develop a binding isotherm. Moreover, there remains an inverse relationship between α-helix and β-turns of bioconjugates during the refolding process. Significantly, in the presence of 12-8-12,2Br⁻, SDS induces more refolding as compared to that for 12-4-12,2Br⁻. Bioconjugation shows an effect on the secondary structures of refolded BSA, which has been explored in detail through various studies such as Fourier transform infrared spectroscopy, fluorescence, and circular dichroism (CD). Therefore, this approach vividly describes the refolding of denatured bioconjugates, exploring structural information regarding various catanions formed during the process that would help in understanding distance-dependent optical biomolecular detection methodologies and physicochemical properties.

Demonstration of refolding of conjugated AuNPs-BSA through the formation of various catanions of SDS and gemini surfactants with different spacers in HEPES buffer medium using FRET/NSET methods and material characterization techniques.

Honey-induced protein stabilization as studied by fluorescein isothiocyanate fluorescence

Protein stabilizing potential of honey was studied on a model protein, bovine serum albumin (BSA), using extrinsic fluorescence of fluorescein isothiocyanate (FITC) as the probe. BSA was labelled with FITC using chemical coupling, and urea and thermal denaturation studies were performed on FITC-labelled BSA (FITC-BSA) both in the absence and presence of 10% and 20% (w/v) honey using FITC fluorescence at 522 nm upon excitation at 495 nm. There was an increase in the FITC fluorescence intensity upon increasing urea concentration or temperature, suggesting protein denaturation. The results from urea and thermal denaturation studies showed increased stability of protein in the presence of honey as reflected from the shift in the transition curve along with the start point and the midpoint of the transition towards higher urea concentration/temperature. Furthermore, the increase in ΔG_D^H₂O and ΔG_D^25°C in presence of honey also suggested protein stabilization.

Utilizing dynamic light scattering as a process analytical technology for protein folding and aggregation monitoring in vaccine manufacturing

Protein aggregation is a common challenge in the manufacturing of biological products. It is possible to minimize the extent of aggregation through timely measurement and in-depth characterization of aggregation. In this study, we demonstrated the use of dynamic light scattering (DLS) to monitor inclusion body (IB) solubilization, protein refolding, and aggregation near the production line of a recombinant protein-based vaccine candidate. Our results were in good agreement with those measured by size-exclusion chromatography. DLS was also used to characterize the mechanism of aggregation. As DLS is a quick, nonperturbing technology, it can potentially be used as an at-line process analytical technology to ensure complete IB solubilization and aggregate-free refolding.

Spectroscopic studies on the interaction of carteolol hydrochloride and urea-induced bovine serum albumin

The interaction of carteolol hydrochloride, to 0.2 mol L(-1) urea-induced bovine serum albumin in aqueous solution has been first investigated by fluorescence spectra and ultraviolet-visible (UV-vis) spectra at pH 7.40. The quenching mechanism, binding parameter and sites (n), the binding mode (ΔG, ΔH, and ΔS) as well as the binding distance (r) have been obtained according to the experimental results. We also use the synchronous fluorescence method to study the effect of CTL on the conformation change of urea-induced BSA.

Binding, unfolding and refolding dynamics of serum albumins

BACKGROUND

The serum albumins (human and bovine serum albumin) occupy a seminal position among all proteins investigated until today as they are the most abundant circulatory proteins. They play the major role of a transporter of many bio-active substances which include various fatty acids, drug molecules, and amino acids to the target cells. Hence, studying the interaction of these serum albumins with different binding agents has attracted enormous research interests from decades. The nature and magnitude of these bindings have direct consequence on drug delivery, pharmacokinetics, therapeutic efficacy and drug design and control.

SCOPE OF THE REVIEW

In the present review, we summarize the binding characteristics of both the serum albumins with surfactants, lipids and vesicles, polymers and dendrimers, nanomaterials and drugs. Finally we have reviewed the effect of various chemical and physical denaturants on these albumins with a special emphasis on protein unfolding and refolding dynamics.

MAJOR CONCLUSIONS

The topic of binding and dynamics of protein unfolding and refolding spans across all areas of inter-disciplinary sciences and will benefit clinical toxicology and medicines. The extensive data from several contemporary research based on albumins will help us to understand protein dynamics in a more illustrious manner.

GENERAL SIGNIFICANCE

These data have immense significance in understanding and unravelling the mechanisms of protein unfolding/refolding and thus can pave the way to prevent protein mis-folding/aggregation which sometimes leads to severe consequences like Parkinson's and Alzheimer's diseases. This article is a part of a Special Issue entitled Serum Albumin. This article is part of a Special Issue entitled Serum Albumin.

Interaction of multimicrobial synthetic inhibitor 1,2-bis(2-benzimidazolyl)-1,2-ethanediol with serum albumin: spectroscopic and computational studies

The molecule, 1,2-Bis(2-benzimidazolyl)-1,2-ethanediol (BBE) is known to act as a selective inhibitor of poliovirus, rhinovirus, Candida albicans, several bacterial species, and is easily synthesized by Phillips reaction. The interaction of BBE with BSA and the effects of its binding on the conformation and unfolding/refolding pathways of the protein were investigated using multispectroscopic techniques and molecular modeling. The binding studies indicate that BSA has one high affinity BBE binding site with association constant 6.02±0.05×10(4) M(-1) at 298 K. By measuring binding at different temperatures, we determined the changes in enthalpy (ΔH = -15.13±2.15 kJ mol(-1)), entropy (ΔS = 40.87±7.25 J mol(-1) K(-1)) and free energy (ΔG( = )26.78±1.02) of interaction, which indicate that the binding was spontaneous and both enthalpically and entropically driven. Based on molecular modeling and thermodynamic parameters, we proposed that the complex formation involved mainly hydrophilic interaction such as hydrogen bonding between hydroxyl groups of ethane-1,2-diol fragment with Tyr410 and benzimidazole sp(2) nitrogen atom with Ser488 and hydrophobic interaction between phenyl ring of one benzimidazole of the ligand and hydrophobic residues namely, Ile387, Cys391, Phe402, Val432 and Cys437. The sequential unfolding mechanism of BSA, site-specific marker displacement experiments and molecular modeling showed that the molecule preferably binds in subdomain IIIA. The BBE binding to BSA was found to cause both secondary and tertiary structural alterations in the protein as studied by intrinsic fluorescence, near-UV and far-UV circular dichroism results. The unfolding/refolding study showed that BBE stabilized native to intermediate states (N⇌I) transition of the protein by ∼2 kJ mol(-1) without affecting the intermediate to unfolded states (I⇌U) transition and general mechanism of unfolding of BSA.

Structural stability as a probe for molecular evolution of homologous albumins studied by spectroscopy and bioinformatics

Equilibrium unfolding by guanidinium hydrochloride (GuHCl) and urea as well as evolutionary trends of two homologous albumins, pig serum albumin (PSA) and rabbit serum albumin (RSA), has been studied with circular dichroism, tryptophanyl fluorescence and bioinformatics. GuHCl cannot distinguish the contribution of electrostatic interactions to the proteins which were otherwise effectively monitored by urea. Higher differences in free energy changes due to urea than GuHCl show electrostatic interactions among charged amino acids are possibly responsible for higher structural stability of RSA in comparison to PSA. From the sequence of HSA and RSA, deletion of arginine at position 117 and the presence of one extra tryptophan at position 135 may possess some clue for lesser stability of PSA. Here, for comparison, chemical unfolding data of HSA and BSA had been taken into consideration. We found that thermodynamically RSA and PSA are closer to HSA and BSA, respectively, in accordance with their sequence homologies. Taxonomically, rabbit belongs to lagomorph which is closer to hominids than ungulates. Hence, on the basis of these thermodynamic data of protein denaturation of different species we can use this new approach to analyze the phylogenetic relationship among the major clades of eutherian mammals to obtain their evolutionary trends.

Biological characteristics of two lysines on human serum albumin in the high-affinity binding of 4Z,15Z-bilirubin-IXα revealed by phage display

4Z,15Z-bilirubin-IXα (4Z,15Z-BR), an endogenous compound that is sparingly soluble in water, binds human serum albumin (HSA) with high affinity in a flexible manner. A phage library displaying recombinant HSA domain II was constructed, after three rounds of panning against immobilized 4Z,15Z-BR, and eight clones with high affinity for the pigment were found to contain conserved basic residues, such as lysine or arginine, at positions 195 and 199. The wild type and two mutants, K195A and K199A, of whole HSA as well as stand-alone domain II were expressed in Pichia pastoris for ligand-binding studies. The binding of 4Z,15Z-BR to the K195A and K199A mutants was decreased in both whole HSA and the domain II proteins. The P-helicity conformer (P-form) of 4Z,15Z-BR was found to preferentially bind to the wild types and the K195A mutants, whereas the M-form bound to the K199A mutants. Photoconversion experiments showed that the P-form of 4Z,15Z-BR was transformed into highly water-soluble isomers at a much faster rate than the M-form. In addition, the M-form of 4Z,15Z-BR showed higher affinity for domain I than for domain II. The present findings suggest that, whereas both Lys195 and Lys199 in subdomain IIA are important for the high-affinity binding of 4Z,15Z-BR, Lys199 plays a more prominent role in the elimination of 4Z,15Z-BR.

Characterization of secondary and tertiary conformational changes of beta-lactoglobulin adsorbed on silica nanoparticle surfaces

Nanoparticles possess unique properties as a result of their large surface area per unit volume and therefore can be functionalized by the immobilization of enzymes for a variety of biosensing applications. Changes in the tertiary conformation of beta-lactoglobulin adsorbed on 90 nm silica nanoparticles with time were inferred using tryptophan fluorescence and Fourier transform infrared spectroscopy (FTIR) for different surface concentrations, temperature, pH, ionic strength, and 2,2,2-trifluoroethanol (TFE) and dithiothreitol (DTT) concentrations. Rapid initial unfolding followed by a much slower rate at longer times was observed, with the extent of unfolding being higher at lower surface concentrations, higher ionic strengths, higher temperature, higher TFE and DTT concentrations, and pI. The effect of temperature on the unfolding of adsorbed protein on the nanoparticle surface was similar to that in the bulk even though the extent of unfolding was higher for adsorbed protein molecules. The results of the extent of change in tertiary conformation using FTIR as indicated by the change in the ratio of amide II'/amide I were consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. Circular dichroism (CD) spectra showed that altering the surface concentration by itself did not change the secondary structure of beta-lactoglobulin on the surface. TFE was found to increase the alpha helix content at the expense of the fraction of the beta sheet, whereas the beta sheet was converted to an unordered conformation in the presence of DTT.

Alkaline phosphatase refolding assisted by sequential use of oppositely charged detergents: a new artificial chaperone system

A novel artificial chaperone system, based on combination of oppositely charged detergents, was elaborated to refold soluble alkaline phosphatase. Upon dilution of urea-denatured alkaline phosphatase to a nondenaturing urea concentration in the presence of the capturing agent, complexes of the detergent and non-native protein molecules are formed and thereby the formation of protein aggregates is prevented. The so-called captured protein is unable to refold from the detergent-protein complex states unless a stripping agent is used to gradually remove the detergent molecules. In that respect, we used detergents with variable charges and tail lengths to initiate and complete the refolding process. The results obtained from various analyses (fluorescence, UV, circular dichroism, surface tension, turbidity measurements and activity assays) indicated that the extent of refolding assistance was different due to detergents structure and also the length of hydrophobic portion of each detergent. These observed differences were attributed to the strong electrostatic interactions among the capturing and stripping detergents used in this investigation. Collectively it is expected that protein refolding process can be achieved easier, cheaper and more efficient, using the new technique reported here.

Substitution of Serine for Non-disulphide-bond-forming Cysteine in Grass Carp (Ctenopharygodon Idellus) Growth Hormone Improves In Vitro Oxidative Renaturation

Native grass carp (Ctenopharygodon idellus) growth hormone, has 5 cysteine amino acid residues, forms two disulphide bridges in its mature form. Recombinant grass carp growth hormone, when over-expressed in E. coli, forms inclusion bodies. In vitro oxidative renaturation of guanidine-hydrochloride dissolved recombinant grass carp growth hormone was achieved by sequential dilution and stepwise dialysis at pH 8.5. The redox potential of the refolding cocktail was maintained by glutathione disulphide/glutathione couple. The oxidative refolded protein is heterogeneous, and contains multimers, oligomers and monomers. The presence of non-disulphide-bond-forming cysteine in recombinant grass carp growth hormone enhances intermolecular disulphide bond formation and also nonnative intramolecular disulphide bond formation during protein folding. The non-disulphide-bond-forming cysteine was converted to serine by PCR-mediated site-directed mutagenesis. The resulting 4-cysteine grass carp growth hormone has improved in vitro oxidative refolding properties when studied by gel filtration and reverse phase chromatography. The refolded 4-cysteine form has less hydrophobic aggregate and has only one monomeric isoform. Both refolded 4-cysteine and 5-cysteine forms are active in radioreceptor binding assay.

Kinetic aspects of alkaline phosphatase refolding in the presence of α-cyclodextrin

To get a better understanding of the molecular aspects of protein folding, the refolding kinetic behavior of guanidine hydrochloride-denatured alkaline phosphatase (ALP) was studied in the presence of alpha-cyclodextrin (alpha-CD) through two different approaches: the dilution additive and the artificial chaperone-assisted methods. It was found that alpha-CD enhanced the recovered activity more than 50% via both approaches while decreased the refolding rate, perhaps due to engaging the hydrophobic patches of the protein in a rigid conformation. In contrast, detergents used in the artificial chaperone method increased the refolding rate significantly. A comparison of the rate constants for the refolding and the activity recovery of denatured ALP in the presence of various concentrations of CD and different kinds of detergents showed that they do not progress in a synchronized pattern. This may be attributed to continuous structural rearrangements in the protein long after the return of enzyme activity. These observations are discussed in terms of kinetic and structural aspects of the refolding pathway.

Guanidine hydrochloride denaturation of human serum albumin originates by local unfolding of some stable loops in domain III

The effect of guanidine hydrochloride (GnHCl) on the global stability of human serum albumin (HSA) has been studied by fluorescence and circular dichroism spectroscopic measurements. The differential stability of native conformation of three HSA domains were explored by using domain-specific ligands, hemin (domain I), chloroform (domain II), bilirubin (at domain I/domain II interface) and diazepam (domain III). GnHCl induced unfolding transition curves as monitored by probes for secondary and tertiary structures were cooperative but noncoincidental. A strong ANS binding to the protein was observed around 1.8 M GnHCl, suggesting existence of intermediate states in the unfolding pathway of HSA. A gradual decrease (in the GnHCl concentration range 0.0-1.8 M) in the binding of diazepam indicates that domain III is the most labile to GnHCl denaturation. A significant increase in the binding of bilirubin up to 1.4 M GnHCl and decrease thereafter leading to complete abolishment of bilirubin binding at around 2.0 M GnHCl suggest favorable rearrangement and separation of domains I and II at 1.4 and 2.0 M GnHCl concentration, respectively. Above 1.6 M GnHCl, decrease of the binding of hemin, a ligand for domain I, chloroform, which binds in domain II and lone tryptophanyl fluorescence (Trp-214 located in domain II) indicate that at higher concentration of GnHCl domains I and II start unfolding simultaneously but the stability of domain I (7.4 Kcal/mol) is much more than domain II (4.3 Kcal/mol). A pictorial model for the unfolding of HSA domains, consistent with all these results, has been formulated, suggesting that domain III is the most labile followed by domain II while domain I is the most stable. A molten globule like state of domain III around 1.8 M GnHCl has also been identified and characterized.

Urea induced unfolding of F isomer of human serum albumin: A case study using multiple probes

The human serum albumin is known to undergo N <==> F (neutral to fast moving) isomerization between pH 7 and 3.5. The N < ==> F isomerization involves unfolding and separation of domain III from rest of the molecule. The urea denaturation of N isomer of HSA shows two step three state transition with accumulation of an intermediate state around 4.8-5.2 M urea concentration. While urea induced unfolding transition of F isomer of HSA does not show the intermediate state observed during unfolding of N isomer. Therefore, it provides direct evidence that the formation of intermediate in the unfolding transition of HSA involves unfolding of domain III. Although urea induced unfolding of F isomer of HSA appears to be an one step process, but no coincidence between the equilibrium transitions monitored by tryptophanyl fluorescence, tyrosyl fluorescence, far-UV CD and near-UV CD spectroscopic techniques provides decisive evidence that unfolding of F isomer of HSA is not a two state process. An intermediate state that retained significant amount of secondary structure but no tertiary structure has been identified (around 4.4 M urea) in the unfolding pathway of F isomer. The emission of Trp-214 (located in domain II) and its mode of quenching by acrylamide and binding of chloroform indicate that unfolding of F isomer start from domain II (from 0.4 M urea). But at higher urea concentration (above 1.6 M) both the domain unfold simultaneously and the protein acquire random coil structure around 8.0 M urea. Further much higher KSV of NATA (17.2) than completely denatured F isomer (5.45) of HSA (8.0 M urea) suggests the existence of residual tertiary contacts within local regions in random coil conformation (probably around lone Trp-214).

Detection and characterization of an acid-induced folding intermediate of endostatin

Endostatin, an important angiogenesis inhibitor, is very acid resistant. We are particularly interested in knowing that whether or not endostatin can form a folding intermediate during acid titration. 1H-NMR, CD spectrum, and ANS binding assay show that endostatin at pH 2.0 contains little tertiary structure, but retains substantial secondary structure with strong ANS binding, and Na2SO4 or TFE is found to strongly stabilize endostatin at pH 2.0. All these observations are consistent with the formation of a folding intermediate at pH 2.0. Kinetics studies show that sulfate anions significantly slow down the process for endostatin to reach its equilibrium state at pH 2.0. A regular increase in the amount of alpha-helix content of the intermediate of endostatin at pH 2.0 is found when the concentration of TFE is increased in the range of 0-40%, suggesting that endostatin has an intrinsic alpha-helical propensity.

Intermediate formation at lower urea concentration in ‘B’ isomer of human serum albumin: a case study using domain specific ligands

The urea-induced unfolding of 'N' isomer (occurring at pH 7.0) and 'B' isomer (occurring at pH 9.0) of human serum albumin was studied by fluorescence and circular dichroism spectroscopic measurements. Urea-induced destabilization in different domains of both the isomers was monitored by using domain specific ligands, hemin (domain-I), chloroform, bilirubin (domain-II), and diazepam (domain-III). Urea-induced denaturation of N and B isomers of HSA showed a two-step, three-state transition with accumulation of intermediates around 4.8-5.2M and 3.0-3.4M urea concentrations, respectively. During first transition (0-4.8M urea for N isomer and 0-3.0M urea for B isomer) a continuous decrease in diazepam binding suggested major conformational changes in domain-III prior to intermediate formation. On the other hand, binding of hemin, a ligand for domain-IB and chloroform, whose binding site is located in domain-IIA remains unchanged up to 5.0M urea for N isomer and 3.0M urea for B isomer. Similarly, fluorescence intensity of Trp-214 that resides in domain-IIA remained unchanged up to the above-said urea concentrations and decreased thereafter. Absence of any decrease in hemin binding, chloroform binding, and Trp-214 fluorescence suggested the non-involvement of domain-IB and domain-IIA in intermediate formation. A significant increase in bilirubin binding prior to intermediate formation showed favorable conformational rearrangement in bilirubin binding cavity formed by loop 4 of domain-IB and loop 3 of domain-IIA. Further, a nearly complete abolishment of bilirubin binding to both isomers around 7.0M and 6.0M urea concentrations, respectively, indicated complete separation of domain-I from domain-II from each other. From these observations it can be concluded that N to B transition of human serum albumin shifted the intermediate formation towards lower urea concentration (3.0-3.4M urea for B isomer as against 4.8-5.2M urea for N isomer). Further both the intermediates were found to possess similar alpha-helical (approximately 39%) content and ligand binding properties.

Isolation and characterization of denatured serum albumin from rats with endotoxicosis

Due to its rapid breakdown in the body, denatured serum albumin has not been identified in biological samples. In this study we attempted to determine whether denatured albumin could be identified in rats with endotoxicosis. Male Wistar rats were injected with lipopolysaccharide (LPS; 5 mg/kg body weight). Plasma albumin concentration decreased to one-third the normal level at 2 days after the injection. By using the purified IgG against the specific epitope of chemically denatured albumin, two immunoreactive plasma proteins (bands D2 and D3) were identified by native PAGE followed by Western blot analysis. The plasma concentration of these two proteins increased significantly at 1 and 1.5 days after LPS injection. Peptide mass fingerprinting using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI/TOF-MS) identified these two proteins as serum albumin. In order to characterize their conformational nature, ion-exchange chromatography was used to isolate D2 and D3 albumins from rats injected with LPS. Far- and near-UV circular dichroism (CD), tryptophan and 1-anilino-8-naphthalenesulfonate (ANS) fluorescence, and proteolytic susceptibility showed conformational alterations in the D2 and D3 albumins as compared with native albumin. These data indicate the presence of denatured albumin in circulating rat plasma, and this fact may contribute to a further understanding of the molecular mechanisms of albumin breakdown in physiological and pathophysiological conditions.