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.     

The conformation of the activation peptide of protein C is influenced by Ca2+ and Na+ binding

Previous studies have suggested that the conformation of the activation peptide of protein C is influenced by the binding of Ca(2+). To provide direct evidence for the linkage between Ca(2+) binding and the conformation of the activation peptide, we have constructed a protein C mutant in the gamma-carboxyglutamic acid-domainless form in which the P1 Arg(169) of the activation peptide is replaced with the fluorescence reporter Trp. Upon binding of Ca(2+), the intrinsic fluorescence of the mutant decreases approximately 30%, as opposed to only 5% for the wild-type, indicating that Trp(169) is directly influenced by the divalent cation. The K(d) of Ca(2+) binding for the mutant protein C was impaired approximately 4-fold compared with wild-type. Interestingly, the conformation of the activation peptide was also found to be sensitive to the binding of Na(+), and the affinity for Na(+) binding increased approximately 5-fold in the presence of Ca(2+). These findings suggest that Ca(2+) changes the conformation of the activation peptide of protein C and that protein C is also capable of binding Na(+), although with a weaker affinity compared with the mature protease. The mutant protein C can no longer be activated by thrombin but remarkably it can be activated efficiently by chymotrypsin and by the thrombin mutant D189S. Activation of the mutant protein C by chymotrypsin proceeds at a rate comparable to the activation of wild-type protein C by the thrombin-thrombomodulin complex.     

Combined multispectroscopic and molecular docking investigation on the interaction between delphinidin‐3‐O‐glucoside and bovine serum albumin

Anthocyanin is one of the flavonoid phytopigments with specific health benefits. The interaction between delphinidin‐3‐O‐glucoside (D3G) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy, ultraviolet‐visible absorption spectroscopy, circular dichroism spectroscopy and molecular modeling. D3G effectively quenched the intrinsic fluorescence of BSA via static quenching. The number of binding sites and binding constant K_a were determined, and the hydrogen bonds and van der Waals forces played major roles in stabilizing the D3G–BSA complex. The distance r between donor and acceptor was obtained as 2.81 nm according to Förster's theory. In addition, the effects of pH and metal ions on the binding constants were discussed. The results studied by synchronous fluorescence, three‐dimensional fluorescence and circular dichroism experiments indicated that the secondary structures of the protein has been changed by the addition of D3G and the α‐helix content of BSA decreased (from 56.1% to 52.4%). Furthermore, the study of site marker competitive experiments and molecular modeling indicated that D3G could bind to site I of BSA, which was in the large hydrophobic cavity of subdomain IIA. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of metal ions on the interaction between bovine serum albumin and berberine chloride extracted from a traditional Chinese Herb coptis chinensis franch

The effect of four metal ions Cu(2+), Ni(2+), Zn(2+) and Co(2+) on the interaction between bovine serum albumin (BSA) and berberine chloride (BC) extracted from a traditional Chinese Herb coptis chinensis franch, was investigated mainly by means of UV and fluorescence spectroscopy in this paper. The four metal ions make the quenching efficacy of BC to BSA higher than that in the absence of these metal ions because of the possible transition of BSA molecular conformation caused by metal ions. It was found that the quenching mechanism is a combination of static quenching with nonradiative energy transfer. In the presence of metal ions, the apparent association constant K(A) and the number of binding sites of BC on BSA are both decreased in a range of 8-19% and 25-28%, respectively, which indicates that the metal ions decrease the binding efficacy of BC on BSA and increase the concentration of free BC simultaneously. The scheme of interaction between BC and BSA in the presence of metal ions is a strong quenching but a weak binding.     

Kinetics of conformational changes induced by the binding of various metal ions to bovine alpha-lactalbumin.

The kinetic effects of the binding of various metal ions (Ca(2+), Cd(2+), Co(2+), Mg(2+), Mn(2+), Sr(2+) and Zn(2+)) to apo bovine alpha-lactalbumin has been monitored by means of stopped-flow fluorescence spectroscopy. Our results show that the measured rate constant for the binding of metal ions to the Ca(2+)-site increases with increasing binding constant. This is, however, not the case for metal ions binding to the Zn(2+)-site. The binding experiments performed at different temperatures allowed us to calculate the activation energy for the transition from the metal-free to the metal-loaded state of the protein. These values do not depend on the nature of the metal ion but are correlated with the type of binding site. As a result, we were able to demonstrate that Mg(2+), a metal ion which was thought to bind to the Ca(2+)-site, shows the same binding characteristics as Co(2+) and Zn(2+) and therefore most likely interacts with the residues belonging to the Zn(2+)-binding site.     

Binding of anti-cardiovascular drug to serum albumin: an insight in the light of spectroscopic and computational approaches

Isoprenaline hydrochloride is a potential cardiovascular drug helps in the smooth functioning of the heart muscles. So, we have performed the binding study of ISO with BSA. This study was investigated by UV absorption, fluorescence, synchronous fluorescence, circular dichroism, etc. The analysis of intrinsic fluorescence data showed the low binding affinity of ISO. The binding constant K_b was 2.8 × 103 M-1 and binding stoichiometry (n) was approximately one and the Gibb’s free energy change at 310 K was determined to be -8.69 kcal mol^?1. Negative Gibb’s free energy change shows the spontaneity of the BSA and ISO interaction. We have found ISO-induced alternation in the UV absorption, synchronous fluorescence and CD spectra in the absence and presence of the quencher indicates the complex formation. In synchronous fluorescence, red shift was obtained because of the complex formation of BSA and ISO. The distance (r) between the BSA (donor) and ISO (acceptor) was 2.89 nm, determined by FRET. DLS measurements interpreted complex formation due to the reduction in hydrodynamic radii of the protein in the presence of the drug. The binding site of ISO was found to be nearer to Trp 134 with the help of molecular docking and the ΔG° was found to be –10.2 kcal mol^?1. The esterase activity result suggests that ISO acts as competitive inhibitor. Thus, this study would help to determine the binding capacity of the drug to the protein which may indicate the efficiency of diffusion of ISO into the blood for the treatment of heart diseases.     

Spectroscopic investigation of the interaction of the toxicant, 2-naphthylamine, with bovine serum albumin

The mechanism of interaction between bovine serum albumin (BSA) and 2-naphthylamine (2-NA) in aqueous solution was investigated by fluorescence spectroscopy, circular dichroism (CD) spectra, and UV-vis spectroscopy. It was proved from fluorescence spectra that the fluorescence quenching of BSA by 2-NA was a result of the formation of complex between 2-NA and BSA, and the binding constants (K(a) ) as well as the numbers of binding sites for 2-NA in BSA were determined according to the modified Stern-Volmer equation. The results of synchronous fluorescence and CD spectra demonstrated 2-NA could decrease the amount of α-helix of BSA, leading to the loosening of protein skeleton. UV-vis spectroscopy and resonance light scattering spectra (RLS) results also suggested the conformation of BSA were changed and the BSA aggregation occured, which could induce toxic effects on the organism.     

Probing the behavior of bovine serum albumin upon binding to atenolol: insights from spectroscopic and molecular docking approaches

Molecular interaction of atenolol, a selective β₁ receptor antagonist with the major carrier protein, bovine serum albumin (BSA), was investigated under imitated physiological conditions (pH 7.4) by means of fluorescence spectroscopy, UV absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and molecular modeling studies. The steady-state fluorescence spectra manifested that static type, due to formation of the atenolol-BSA complex, was the dominant mechanism for fluorescence quenching. The characteristic information about the binding interaction of atenolol with BSA in terms of binding constant (K_b) were determined by the UV–vis absorption titration, and were found to be in the order of 10³ M^?1 at different temperatures, indicating the existence of a weak binding in this system. Thermodynamic analysis revealed that the binding process was primarily mediated by van der Waals force and hydrogen bonds due to the negative sign for enthalpy change (ΔH⁰), entropy change (ΔS⁰). The molecular docking results elucidated that atenolol preferred binding on the site II of BSA according to the findings observed in competitive binding experiments. Moreover, via alterations in synchronous fluorescence, three-dimensional fluorescence and FT-IR spectral properties, it was concluded that atenolol could arouse slight configurational and micro-environmental changes of BSA.     

The metallomics approach: use of Fe(II) and Cu(II) footprinting to examine metal binding sites on serum albumins

Metal binding to serum albumins is examined by oxidative protein-cleavage chemistry, and relative affinities of multiple metal ions to particular sites on these proteins were identified using a fast and reliable chemical footprinting approach. Fe(ii) and Cu(ii), for example, mediate protein cleavage at their respective binding sites on serum albumins, in the presence of hydrogen peroxide and ascorbate. This metal-mediated protein-cleavge reaction is used to evaluate the binding of metal ions, Na(+), Mg(2+), Ca(2+), Al(3+), Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ce(3+) to albumins, and the relative affinities (selectivities) of the metal ions are rapidly evaluated by examining the extent of inhibition of protein cleavage. Four distinct systems Fe(II)/BSA, Cu(II)/BSA, Fe(II)/HSA and Cu(II)/HSA are examined using the above strategy. This metallomics approach is novel, even though the cleavage of serum albumins by Fe(II)/Cu(II) has been reported previously by this laboratory and many others. The protein cleavage products were analyzed by SDS PAGE, and the intensities of the product bands quantified to evaluate the extent of inhibition of the cleavage and thereby evaluate the relative binding affinities of specific metal ions to particular sites on albumins. The data show that Co(II) and Cr(III) showed the highest degree of inhibition, across the table, followed by Mn(II) and Ce(III). Alakali metal ions and alkaline earth metal ions showed very poor affinity for these metal sites on albumins. Thus, metal binding profiles for particular sites on proteins can be obtained quickly and accurately, using the metallomics approach.     

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     

Analysis of ATP binding to CheA containing tryptophan substitutions near the active site

Signal transduction in the chemotaxis system of Escherichia coli involves an autophosphorylating protein histidine kinase, CheA. At the active site of CheA, phenylalanine residues 455 and 459 occupy positions near the ATP-binding pocket, immediately adjacent to one of the hinge regions of a loop that undergoes an ATP-induced conformational change ("lid closure") that has been characterized previously in X-ray crystal structures [Bilwes et al. (2001) Nat. Struct. Biol. 8, 353-360]. We generated versions of CheA carrying F455W and F459W replacements and investigated whether the fluorescence properties of the introduced tryptophan side chains were affected by nucleotide binding in a manner that would provide a signal for investigating the dynamics of active site events, such as ATP binding and lid closure. Our results indicate that CheA(F455W) is useful in this regard, but CheA(F459W) is not. CheA(F455W) retained full catalytic activity and exhibited easily monitored fluorescence changes upon binding nucleotide: we observed a 25-30% decrease in CheA(F455W) fluorescence emission intensity at 330 nm upon binding ATP in the absence of Mg(2+); in the presence of Mg(2+), the emission spectrum of the CheA(F455W):ATP complex was red-shifted by 5 nm and exhibited an increased intensity (approximately 20% higher at 345 nm relative to that of uncomplexed CheA(F455W)). Different fluorescence changes were observed when two ATP analogues (ADPNP and ADPCP) were used instead of ATP and when Mn(2+) or Ca(2+) was used in place of Mg(2+). We exploited the fluorescence changes induced by Mg(2+)-ATP to explore the kinetics and mechanism of nucleotide binding by CheA(F455W). In the absence of Mg(2+), binding appears to involve a simple one-step equilibrium (k(assn) = 0.7 microM(-1) s(-1) and k(dissn) = 270 s(-1) at 4 degrees C). In the presence of Mg(2+), the binding mechanism involves at least two steps: (i) rapid, relatively weak binding followed by (ii) a rapid, reversible step (k(forward) = 300 s(-1) and k(reverse) =15 s(-1) at 4 degrees C) that enhanced the overall affinity of the complex and generated an increase in W455 fluorescence. This second step could reflect a conformational change at the CheA active site, such as lid closure. These results provide the first insight into the dynamics of nucleotide binding and substrate-induced conformational changes at the active site of a protein histidine kinase.     

Flavonoid-serum albumin complexation: determination of binding constants and binding sites by fluorescence spectroscopy

After a meal rich in plant products, dietary flavonols can be detected in plasma as serum albumin-bound conjugates. Flavonol-albumin binding is expected to modulate the bioavailability of flavonols. In this work, the binding of structurally different flavonoids to human and bovine serum albumins is investigated by fluorescence spectroscopy using three methods: the quenching of the albumin fluorescence, the enhancement of the flavonoid fluorescence, the quenching of the fluorescence of the quercetin-albumin complex by a second flavonoid. The latter method is extended to probes whose high-affinity binding sites are known to be located in one of the two major subdomains (warfarin and dansyl-L-asparagine for subdomain IIA, ibuprofen and diazepam for subdomain IIIA). Overall, flavonoids display moderate affinities for albumins (binding constants in the range 1-15 x 10(4) M(-1)), flavones and flavonols being most tightly bound. Glycosidation and sulfation could lower the affinity to albumin by one order of magnitude depending on the conjugation site. Despite multiple binding of both quercetin and site probes, it can be proposed that the binding of flavonols primarily takes place in subdomain IIA. Significant differences in affinity and binding location are observed for the highly homologous HSA and BSA.     

Effect of ionic strength on the binding of ascorbate to albumin

A fluorophore-nitroxide free radical dual-functional probe (FN) was utilized to study the kinetics of ascorbate (AH(-)) binding to Bovine Serum Albumin (BSA). Since the free radical fragment in the FN probe intramolecularly quenches fluorescence, ascorbate reduction of the nitroxide function is accompanied by a concomitant fluorescence intensity increase from the fluorophore. Thus, both fluorescence and the EPR techniques could be utilized to measure the reaction rate. In the presence of BSA protein, the observed rate of the overall process is the sum of that from at least two reactions: the reaction between free ascorbate and free probe, and the reaction between bound ascorbate and bound probe. Our findings show that the observed rate is strongly dependent on the ionic strength of the medium. A corollary of this observation is the indication of a purely electrostatic interaction between ascorbate and the BSA protein. This conclusion was further corroborated by 1H NMR measurement of the transverse relaxation time, T(2), of ascorbate protons in BSA solutions. Ascorbate ion was released from the ascorbate/BSA ensemble in the presence of increasing concentrations of NaCl. Binding constants of AH(-) to BSA were calculated at different ionic strengths at pH 7.4. Furthermore, an increase in ionic strength did not affect the ability of albumin to protect ascorbate against autoxidation. This suggests that the protein's protective antioxidant effect may be attributed to BSA binding of trace quantities of transition-metal cations (rather than ascorbate binding to BSA). This conclusion is supported by ascorbate UV-absorption measurements in the presence of albumin and Cu(2+) ions as a function of ionic strength.     

Cobalt- and nickel-binding property of cullin-2.

Treatment with divalent metal ions such as cobalt (Co(2+)) or nickel (Ni(2+)) result in the stabilization of hypoxia-inducible factor-1alpha (HIF1alpha). Recently, HIF1alpha was shown to be ubiquitinated by an E3-ligase complex and be subsequently targeted for proteasomal degradation. In this study, we demonstrated that Co(2+) and Ni(2+) specifically bind to cullin-2. Mutant analysis revealed that cullin-2 possesses at least three sites for the binding. Furthermore, fluorescence spectroscopy revealed that only Co(2+) and Ni(2+) have the binding activity to cullin-2, but other metal ions, including Cu(2+), Ca(2+), Mg(2+), Mn(2+), and Zn(2+), did not. Finally, we found that Co(2+) and Ni(2+) do not bind to any components of the E3-ligase other than cullin-2, suggesting that cullin-2 is a key target of Co(2+) and Ni(2+). Interestingly, Co(2+) did not affect the complex formation of the ligase, suggesting that the metal binding to cullin-2 affects the function, but not the assembly of the E3-ligase.     

Binding of La3+ to calmodulin and its effects on the interaction between calmodulin and calmodulin binding peptide, polistes mastoparan

Binding of La(3+) to calmodulin (CaM) and its effects on the complexes of CaM and CaM-binding peptide, polistes mastoparan (Mas), were investigated by nuclear magnetic resonance (NMR) spectroscopy, fluorescence and circular dichroism spectroscopy, and by the fluorescence stopped-flow method. The four binding sites of La(3+) on CaM were identified as the same as the binding sites of Ca(2+) on CaM through NMR titration of La(3+) to uniformly (15)N-labeled CaM. La(3+) showed a slightly higher affinity to the binding sites on the N-terminal domain of CaM than that to the C-terminal. Large differences between the (1)H-(15)N heteronuclear single quantum coherence (HSQC) spectra of Ca(4)CaM and La(4)CaM suggest conformational differences between the two complexes. Fluorescence and CD spectra also exhibited structural differences. In the presence of Ca(2+) and La(3+), a hybrid complex, Ca(2)La(2)CaM, was formed, and the binding of La(3+) to the N-terminal domain of CaM seemed preferable over binding to the C-terminal domain. Through fluorescence titration, it was shown that La(4)CaM and Ca(2)La(2)CaM had similar affinities to Mas as Ca(4)CaM. Fluorescence stopped-flow experiments showed that the dissociation rate of La(3+) from the C-terminal domain of CaM was higher than that from the N-terminal. However, in the presence of Mas, the dissociation rate of La(3+) decreased and the dissociation processes from both global domains were indistinguishable. In addition, compared with the case of Ca(4)CaM-Mas, the slower dissociations of Mas from La(4)CaM-Mas and Ca(2)La(2)CaM-Mas complexes indicate that in the presence of La(3+), the CaM-Mas complex became kinetically inert. A possible role of La(3+) in the Ca(2+)-CaM-dependent pathway is discussed.     

The interaction of blood proteins with brucine

The features of brucine (BC) binding to two blood proteins, bovine hemoglobin (BHb), and bovine serum albumin (BSA), were investigated via fluorescence, circular dichroism and UV/Vis absorption spectroscopy. The results revealed that BC caused the fluorescence quenching of blood proteins by the formation of BC–protein complex. The corresponding thermodynamic parameters were measured at different temperatures. The process of binding BC molecule on protein was a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased. Hydrophobic and electrostatic interactions play a major role in stabilizing the complex. The molecular docking has been employed to explore the binding site of the BC in BHb and BSA on the Autodock 4.2. The distances r between BC and protein were calculated to be 4.93 and 5.08 nm for BHb, and BSA, respectively. The effect of BC on the conformation of blood proteins was analyzed using CD, synchronous fluorescence and three-dimensional fluorescence spectra.     

Effect of quercetin on the amiloride–bovine serum albumin interaction using spectroscopic methods,molecular docking and chemometric approaches

The effect of quercetin flavonoid (QUE), on the binding interaction of antihypertensive drug, amiloride (AMI) with bovine serum albumin (BSA) was investigated in this study. Spectroscopic methods such as steady‐state, synchronous, three‐dimensional fluorescence, and circular dichroism spectroscopy were employed to study the interaction. Fluorescence data were analyzed using the Stern–Volmer equation and a static quenching process was found to be involved in the formation of AMI–BSA and QUE–BSA complexes and were in good agreement with the thermodynamic study. The thermodynamic parameters illustrated that the process is spontaneous and enthalpy driven. Hydrophobicity is acting as the primary force in the binding interaction. Fluorescence spectral data were resolved using a multivariate curve resolution‐alternating least squares method (MCR–ALS). Site marker and molecular docking studies confirmed the binding site of AMI on BSA, i.e. site II. The binding distance between amino acid of BSA and AMI was calculated and found to be 2.18 nm which indicated that energy transfer has occurred from an amino acid of BSA to AMI. The binding affinity of AMI to BSA was found to be reduced in the presence of QUE, which may lead to the poor distribution of AMI at the desired site.     

Binding of cationic porphyrin to isolated DNA and nucleoprotein complex: quantitative analysis of binding forms under various experimental conditions

We studied the complex formation of tetrakis(4-N-methylpyridyl)porphyrin (TMPyP) with double stranded DNAs and T7 phage nucleoprotein complex. We analyzed the effect of base pair composition of DNA, the presence of capsid protein, and the composition of the microenvironment on the distribution of TMPyP between binding forms as determined by the decomposition of porphyrin absorption spectra. No difference was found in the amount of bound TMPyP between DNAs of various base compositions; however, the ratio of TMPyP binding forms depends on the AT/GC ratio. The presence of protein capsid opposes the binding of TMPyP to DNA. This behavior offers a possibility to investigate the protein capsid integrity due to the analysis of porphyrin binding. Increasing ionic strength of monovalent ions decreases the amount of bound porphyrin through the inhibition of intercalation, but does not influence the quantity of groove-binding forms when TMPyP interacts with isolated DNA. In the case of the nucleoprotein complex the groove-binding is also inhibited already at 140 mM ionic strength. The presence of 1 mM divalent cations (Mg(2+), Ca(2+), Cu(2+) and Ni(2+)) in a buffer solution of 70 mM ionic strength does not influence significantly the free to bound ration of TMPyP when it interacts with isolated DNA. The contribution of binding forms is remarkably different in Mg(2+)/Ca(2+) and Cu(2+)/Ni(2+) containing solutions. Transition metals significantly decrease the binding sites for intercalation in both DNA and nucleoprotein complex, but facilitate the groove-binding of TMPyP to isolated DNA.     

Multistep binding of transition metals to the H-N-H endonuclease toxin colicin E9

We report the first stopped-flow fluorescence analysis of transition metal binding (Co(2+), Ni(2+), Cu(2+), and Zn(2+)) to the H-N-H endonuclease motif within colicin E9 (the E9 DNase). The H-N-H consensus forms the active site core of a number of endonuclease groups but is also structurally homologous to the so-called treble-clef motif, a ubiquitous zinc-binding motif found in a wide variety of metalloproteins. We find that all the transition metal ions tested bind via multistep mechanisms. Binding was further dissected for Ni(2+) and Zn(2+) ions through the use of E9 DNase single tryptophan mutants, which demonstrated that most steps reflect conformational rearrangements that occur after the bimolecular collision, many common to the two metals, while one appears specific to zinc. The kinetically derived equilibrium dissociation constants (K(d)) for transition metal binding to the E9 DNase agree with previously determined equilibrium measurements and so confirm the validity of the derived kinetic mechanisms. Zn(2+) binds tightest to the enzyme (K(d) approximately 10(-)(9) M) but does not support endonuclease activity, whereas the other metals (K(d) approximately 10(-)(6) M) are active in endonuclease assays implying that the additional step seen for Zn(2+) traps the enzyme in an inactive but high affinity state. Metal-induced conformational changes are likely to be a conserved feature of H-N-H/treble clef motif proteins since similar Zn(2+)-induced, multistep binding was observed for other colicin DNases. Moreover, they appear to be independent both of the conformational heterogeneity that is naturally present within the E9 DNase at equilibrium, as well as the conformational changes that accompany the binding of its cognate inhibitor protein Im9.     

Spectroscopic investigation on the interaction of Cr(VI) with bovine serum albumin

The interaction of potassium dichromate (Cr(VI)) with bovine serum albumin (BSA) was investigated by fluorescence, synchronous fluorescence, resonance light scattering (RLS), ultraviolet-visible absorption, and circular dichroism (CD) spectroscopies under simulated physiological conditions. The experimental results showed that Cr(VI) could quench the intrinsic fluorescence of BSA following a static quenching process, which indicates the formation of a Cr(VI)-BSA complex. The binding constant (KA) and binding site (n) were measured at different temperatures. The spectroscopic results also revealed that the binding of Cr(VI) to BSA can lead to the loosening of the protein conformation and can change the microenvironment and skeleton of BSA.