Flow birefringence of T2 bacteriophage DNA

The streaming birefringence and extinction angles of DNA from T2 bacteriophage in neutral aqueous buffers have been determined over a range of concentrations from 5 to 44 μg./ml. and of velocity gradients from 5 to 50 sec.^?1. Although the extinction angles are relatively small even at the lowest velocity gradients and concentrations studied, a lower limit estimate of the limiting extinction angle to shear rate ratio can be made, and this value is interpreted in terms of available dynamical theory. The statistical segment length has been estimated from the birefringence data as ～ 1100 A. This figure is in satisfactory agreement with the results of independent calculations by others.     

A comparison of five methods for obtaining the intrinsic viscosity of bovine serum albumin

Intrinsic viscosity [η] is a characteristic of proteins and other molecules related directly to their ability to disturb flow and indirectly to their size and shape. It is usually determined by extrapolating reduced viscosity to zero concentration. Four other methods for deriving [η] have been utilized by previous investigators. Studies of the intrinsic viscosity of bovine serum albumin had been carried out two years apart as a test of viscometry technique; the data obtained were used to compare the five methods. Four of the five produced [η] values ranging from 3.92 to 4.21 ml/g. Agreement was good between the two studies. The five methods were compared to each other using linearity of regression, statistical error of determination, effect of varying solvent time, and result obtained in different concentration ranges. By these four criteria, use of the regression of specific fluidity (1 ? 1/η_rel) with concentration was found superior to other methods. Its only deficiency was a requirement that solution density be corrected for at each concentration studied rather than applying a single correction for density after using kinematic viscosity data. All methods for deriving intrinsic viscosity are based on one of three equations; flow is expressed either in terms of reduced viscosity (Huggins), inherent viscosity (Kraemer), or specific fluidity. Of these three equations, specific fluidity is the most closely related both to theoretical analyses and to experimental studies of rigid spheres. There is abundant evidence in past reports that in contrast to rigid spheres, flexible polymers do not produce a linear rise in specific fluidity as their concentration increases, strongly suggesting that their molecular conformation is changing with concentration. A linear relation between fluidity and concentration has been observed for almost all proteins and protein mixtures studied. When this linear relation is present it indicates both that molecular conformation during flow is independent of concentration in the range studied and that the specific fluidity method for deriving intrinsic viscosity is the most appropriate.     

Intrinsic viscosity of bovine serum albumin conformers

Intrinsic viscosity of bovine serum albumin (BSA) at different pH values (2.7, 4.3, 7.4, 8 and 10) has been determined, as well as the Mark-Houwink constant and expansion factor. The traditional technique for data analysis using extrapolation to obtain intrinsic viscosity values shows an unusual behavior regarding concentration that can be observed in the values obtained for Huggins' and Kraemer's constants.     

Transient electric birefringence studies of T2 bacteriophage and T2 ghost

The transient electric birefringence behavior of bacteriophage T2 and the T2 ghost or protein coal was studied. The field free relaxation measurements show both the intact virus and its ghost to have two rotary diffusion coefficients. These coefficients have values of 555 ± 54 and 111 ± 22 sec.^?1 for the intact virus and 688 ± 89 and 161 ± 29 sec.^?l for the ghost. The equivalent ellipsoids for the fast and slow relaxation coefficients were obtained by use of Perrin's equation and were related to the bacteriophage structure in terms of a possible extension of the tail fibers or an enlargement of the head structure. The saturation of the specific birefringence of the phage and the ghost when compared with the specific birefringence of the free nucleic acid gave an average optical orientation of 10 to 18% of the nucleic acid parallel to the main axis of the phage. The analysis of the birefringence versus applied field strength in the Kerr region gave the following values for the anisotropy of the polarixability. α_e,33 – α_e,11 and intrinsic dipole, μ, of both phage and ghost : for T2 phage α_e,33 – α_e,11 = 5.0 × 10^?14 cm.³ and μ = 64,400 Debyes; for T2 ghost α_e,33 – α_e,11 = 7.9 × 10^?14cm.³ and μ = 57,200 Debyes. The high intrinsic dipole for phage and ghost is interpreted as to be associated with the mechanisms of the virus for attachment, to the host cell wall.     

Quenching of the intrinsic fluorescence of bovine serum albumin by phenylfluorone-Mo(VI) complex as a probe

In this paper, the binding characteristics of bovine serum albumin (BSA) and phenylfluorone (PF)-molybdenum (Mo(VI)) complex have been studied by fluorophotometry. The binding constants are calculated at different temperatures. The binding distance and the energy transfer efficiency between PF-Mo(VI) complex and protein are obtained on the basis of the theory of Forster energy transfer. DeltaH and DeltaS are calculated to be -7.11 kJ mol-1 and 70.30 J mol-1 K-1, which indicate that electrostatic force plays major role in the interaction of PF-Mo(VI) complex and BSA. The experimental results show that BSA and PF-Mo(VI) complex have strong interactions and the mechanism of quenching belongs to static quenching.     

Sedimentation and intrinsic viscosity behavior of PM2 bacteriophage DNA in alkaline solution

The sedimentation coefficient and intrinsic viscosity of nicked and closed circular PM2 bacteriophage DNA have been measured as a function of pH in the alkaline region. A gradual increase in the sidimentation coefficient, and a corresponding decrease in the intrinsic viscosity, are observed for the superhelical (closed) circle in the pH region from 10.5 to about 10.9. This has been tentatively interpreted in terms of the known dependence of sedimentation coefficient upon the number of superhelical turns. At slightly higher pH values, the curve passes through the minimum (sedimentation coefficient) and maximum (intrinsic viscosity) expected when the superhelical turns present at neutral pH are unwound by partial alkaline denaturation. Sedimentation studies of the relaxed (nicked) circular species have revealed the existence of DNA forms in the pH region from 11.27 to 11.37 which sediment considerably faster than the closed circle in the same pH region. These have been identified as partially denatured nicked circles, in which varying fractions of the duplex structure have undergone alkaline denaturation, but strand separation has not yet occurred. Varying fractions of a slower species, either undenatured or completely denatured nicked circles, are also observed in some of these experiments. A corresponding result is observed in the intrinsic viscosity vs. pH curve. When nicked circular PM2 DNA is exposed to various alkaline pH's, rapidly neutralized, and sedimented at neutral pH, the expected sharp transition from native to denatured (strand-separated) molecules is seen. However, a very narrow pH range is noted in which native and denatured forms coexist in a single experiment. The above experiments carried out upon the closed form also reveal a narrow pH range in which the bulk of the transition from native closed circles to the collapsed cyclic coil takes place, in acccord with an earlier study on a different DNA. This transition is shown never to be completely effected, however, as there is a fraction (7–8%)of the closed circles which renature to the native form, regardless of the alkaline pH employed. This same phenomenon was not observed in the case of artificially closed λb₂b₅c DNA circles. Possible explanations for some of the above results are discussed.     

Spectroscopic studies of bovine serum albumin adsorbed onto magnetic–thermosensitive carbon microspheres

To investigate the influence of magnetic–thermosensitive carbon microspheres (MTCMSs) as a targeting drug carrier on serum albumins in vitro, in this study, bovine serum albumin (BSA) was chosen as a template protein to explore the interaction between serum proteins and MTCMSs. Fluorescence spectrophotometry, ultraviolet–visible absorbance (UV–vis) spectrophotometry and circular dichroism spectrometry were used to investigate the interaction between MTCMSs and BSA. Results indicate that BSA interacts with MTCMSs and the fluorescence intensity of BSA is quenched by 50% in a static quenching at 310 K when the concentration of MTCMSs reaches 30 mg/L. Thermodynamic parameters including free energy change (△G^θ), enthalpy change (△H^θ) and entropy change (△S^θ) were calculated. The results (△G^θ < 0, △H^θ < 0 and △S^θ > 0) suggest a spontaneous process and the formation of a hydrogen bond between MTCMSs and BSA. UV–vis measurements reveal that the micro‐environment of an amino acid residue is altered in the presence of MTCMSs. The α‐helix content of BSA decreases by 4% and the β‐sheet content increases by 3.2% with increasing concentrations of MTCMSs to 30 mg/L, illustrating a change in the skeletal structure of BSA. These results demonstrate that MTCMSs as a targeting drug carrier impact the structure of serum albumins. This work provides not only a theoretical basis of BSA adsorption onto MTCMSs, but also an understanding of safe drug carriers in biomedicine. Copyright © 2016 John Wiley & Sons, Ltd.     

The Interaction of BODIPY with bovine serum albumin and its bilirubin complex

Using fluorescence and electronic spectroscopy the interaction of boron-dipyrromethene complex (BODIPY) with bovine serum albumin (BSA) and its bilirubin macromolecular complex (BR·BSA) in aqueous solution was investigated. The interaction of BODIPY is carried out by the static quenching of protein fluorescence and is predominantly hydrophobic and electrostatic in nature. The values of the binding constants were (61.2 ± 2.8) · 10³ and (6.51 ± 0.3) · 10³ M^?1. The interaction of BODIPY with proteins leads to the observed hypso- and bathochromic shift in BODIPY absorption band. Forster resonance energy transfer theory allowed of determing the donor-ligand distance, which were 2.88 and 2.46 nm for BSA and BR·BSA, respectively. Using synchronous fluorescence spectroscopy it was possible to reveal features of BODIPY influence on conformational changes in protein molecules. It was established that BODIPY more effectively interacts with BSA compared to BR·BSA.     

Electrostatic interaction and complex formation between gum arabic and bovine serum albumin

The interaction of gum arabic (GA) and bovine serum albumin (BSA) has been investigated through turbidity and light scattering intensity measurements and by the use of dynamic light scattering, laser Doppler velocimetry, and isothermal titration calorimetry. It has been shown that GA and BSA can form soluble and insoluble complexes depending on the solution pH and the mixing ratio and is a function of the net charge on the complex. Soluble complexes were obtained when the electrophoretic mobility was greater than ±1. 5 μm s(-1) V(-1) cm(-1). Changes in the value of the isoelectric point of the complexes with mixing ratio and isothermal titration calorimetric data indicated that complexes formed at pHs 3 and 4 consisted of ～60 BSA molecules for every GA molecule, while at pH 5 there were ～10 BSA molecules per GA molecule. Calorimetric studies also indicated that the interaction occurred in two stages at both pH 3 and pH 4, but that the nature of the interaction at these two pH values was significantly different. This was attributed to differences in the relative magnitude of the positive and negative charges on the BSA and GA, respectively, and possibly due to changes in the BSA conformation. The fact that there is an interaction at pH 5, which is above the isoelectric point of the BSA, is due to the interaction of the carboxylate groups on the GA with positive patches on the BSA or to the charge regulation of the protein-polysaccharide system brought about by changes in dissociation equilibria. Complexation is reduced as the ionic strength of the solvent increases and is prevented at a NaCl concentration of 120 mM.     

l-Arginine reduces thioflavin T fluorescence but not fibrillation of bovine serum albumin

This work examines the effects of l-arginine (l-Arg) on the aggregation and amyloid fibrillation of bovine serum albumin (BSA). We demonstrate that l-Arg dose-dependently reduces thioflavin T (ThT) fluorescence of BSA within the l-Arg concentration range used (0–1.4 M). However, as revealed by electron microscopy, size exclusion chromatography, and dynamic light scattering results, l-Arg does not prevent amyloid-like fibril formation by BSA. We conclude that l-Arg competes against ThT for binding sites on BSA amyloid-like fibrils, leading to biased results in ThT fluorescence measurements. Moreover, the use of ThT fluorescence assay to screen for potential inhibitors against amyloid fibrillation can give misleading results.     

Copper II complex of a tridentate ligand: an artificial metalloprotease for bovine serum albumin

A copper(II) complex of 2, 6-bis(benzimidazo-2-yl) pyridine was synthesized and its binding properties with bovine serum albumin (BSA) has been evaluated. The binding plot obtained from the absorption titration data gives a binding constant of 2.4 (+/-0.3) x10(3) M(-1). It was found that the charge transfer band of the metal complex was perturbed in the presence of BSA. The gel electrophoresis pattern of BSA incubated with copper(II) complex shows the metalloproteolytic activity of the metal complex. In the presence of oxygen, protein undergoes site-specific cleavage by binding to the histidine residues of domain III, with the resultant formation of four fragments of molecular weight 49, 45, 22 and 17 kDa. This indicates the presence of two specific binding sites in the protein molecule. In the absence of molecular oxygen, the metal complex was found unable to cleave the protein. The circular dichroism (CD) spectrum of the isolated fragments shows nearly 38% and 32% of alpha helical content in 49 and 45 kDa fragments, respectively, which shows that the cleavage leads to no changes in the secondary structure of the protein fragments.     

Aggregation and fibrillation of bovine serum albumin

The all-alpha helix multi-domain protein bovine serum albumin (BSA) aggregates at elevated temperatures. Here we show that these thermal aggregates have amyloid properties. They bind the fibril-specific dyes Thioflavin T and Congo Red, show elongated although somewhat worm-like morphology and characteristic amyloid X-ray fiber diffraction peaks. Fibrillation occurs over minutes to hours without a lag phase, is independent of seeding and shows only moderate concentration dependence, suggesting intramolecular aggregation nuclei. Nevertheless, multi-exponential increases in dye-binding signal and changes in morphology suggest the existence of different aggregate species. Although beta-sheet content increases from 0 to ca. 40% upon aggregation, the aggregates retain significant amounts of alpha-helix structure, and lack a protease-resistant core. Thus BSA is able to form well-ordered beta-sheet rich aggregates which nevertheless do not possess the same structural rigidity as classical fibrils. The aggregates do not permeabilize synthetic membranes and are not cytotoxic. The ease with which a multidomain all-alpha helix protein can form higher-order beta-sheet structure, while retaining significant amounts of alpha-helix, highlights the universality of the fibrillation mechanism. However, the presence of non-beta-sheet structure may influence the final fibrillar structure and could be a key component in aggregated BSA's lack of cytotoxicity.     

Thermodynamics of the slow–fast transition in bacteriophage T2L

We have measured the thermodynamic parameters of the slow-fast tail-fiber reorientation transition on T2L bateriophage. Proportions of the virus in each form were determined from peak-height measurements in sedimention-velocity runs and from average diffusion coefficients obtained by quasielastic laser light scattering. Computer simulation of sedimentation confirmed that there were no undetected intermediates in the transition, which was analyzed as a two-state process. Van't Hoff-type plots of the apparent equilibrium constant and of the pH midpoint of the transition as function of reciprocal temperature led to the following estimates of the thermodynamic parameters for the transition at pH 6.0 and 20°C: ΔH° = ?139 ± 18Kcal mol^?1, ΔS° = ?247 ± 46 cal K^?1 mol^?1, and ΔG° = ?66 ± 22 kcal mol^?1. Per mole of protons taken up in the transition, the analogous quantities were ?15.9 ± 1.7 kcal mol^?1, ?26.3 ± 2.2 cal K^?1 mol^?1, and ?8.22 ± 1.8 kcal mol^?1. The net number of protons taken up was about 8.5 ± 1.5. The large values of the thermodynamic functions are consistent with a highly cooperative reaction and with multiple interactions between the fibres and the remainder of the phage. The negative entropy of the transition is probably due to immobilization of the fibres.     

1H- and 2H-NMR study of bovine serum albumin solutions

Frozen, native and denatured bovine serum albumin solutions have been studied with a wide-band NMR pulse spectrometer. Both macromolecular and water protons spin-spin and spin-lattice relaxation times--t2m, t1m, t2w, t1w--have been measured between 170 and 360 K. In the native sample, the t2m process is the tumbling rate of the bovine serum albumin molecules. It gives to the spin-lattice relaxation an omega 0(-2) frequency dependence at room temperature in the studied frequency range, 6-90 MHz. An additional process contributes to t1m-1; it arises from internal backbone or segmental motions and provides a lower frequency behaviour. On denaturation, bovine serum albumin molecules lose their tumbling motion and form a rigid network, while internal backbone motions seem unaffected. Calorimetric Cp measurement confirms the occurrence of a phase transition upon denaturation. 1H and 2H spin-lattice relaxation times of water protons depend mainly on bound water mobility. 1H and 2H t2w depend also on the tertiary structure of bovine serum albumin and on its mobility, because of a fast exchange process between water and some protein protons (or deutons), while a cross-relaxation process between protein and water protons contributes to 1H t1w. Denaturation has no influence on bound water motional properties and bound water population.     

Characterization of the binding of 2‐mercaptobenzimidazole to bovine serum albumin

2‐Mercaptobenzimidazole (MBI) is widely utilized as a corrosion inhibitor, copper‐plating brightener and rubber accelerator. The residue of MBI in the environment is potentially harmful to human health. In this article, the interaction of MBI with bovine serum albumin (BSA) was explored using spectroscopic and molecular docking methods under physiological conditions. The positively charged MBI can spontaneously bind with the negatively charged BSA through electrostatic forces with one binding site. The site marker competition experiments and the molecular docking study revealed that MBI bound into site II (subdomain IIIA) of BSA, which further led to some secondary structure and microenvironmental changes of BSA. This work provides useful information on understanding the toxicological actions of MBI at the molecular level. Copyright © 2015 John Wiley & Sons, Ltd.     

Interaction of ergosterol with bovine serum albumin and human serum albumin by spectroscopic analysis

This study was designed to examine the interactions of ergosterol with bovine serum albumin (BSA) and human serum albumin (HSA) under physiological conditions with the drug concentrations in the range of 2.99-105.88?μM and the concentration of proteins was fixed at 5.0?μM. The analysis of emission spectra quenching at different temperatures revealed that the quenching mechanism of HSA/BSA by ergosterol was the static quenching. The number of binding sites n and the binding constants K were obtained at various temperatures. The distance r between ergosterol and HSA/BSA was evaluated according to F?ster non-radioactive energy transfer theory. The results of synchronous fluorescence, 3D fluorescence, FT-IR, CD and UV-Vis absorption spectra showed that the conformations of HSA/BSA altered in the presence of ergosterol. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) for BSA-ergosterol and HSA-ergosterol systems were calculated by the van't Hoff equation and discussed. Besides, with the aid of three site markers (for example, phenylbutazone, ibuprofen and digitoxin), we have reported that ergosterol primarily binds to the tryptophan residues of BSA/HSA within site I (subdomain II A).     

The subsequent effect of interaction between Co(2+) and human serum albumin or bovine serum albumin.

A notable hysteretic effect has been observed in the interaction of Co(II) with human serum albumin (HSA) or bovine serum albumin (BSA) using UV-Visible spectrometry at physiological pH (7.43), which shows that the binding between Co(II) and HSA or BSA may induce a slow transition of HSA or BSA from the conformation of weaker affinity for Co(II) to one of stronger affinity (A-B transition). The rate constants and activation parameters of this transition were measured and are discussed. It is inferred that such a conformation transition may occur due to the binding of the first Co(II) ion with the peptide segment of N-terminal residues 1-3, which results in a 'hinged movement' of the relatively hydrophobic 'valley' in the IA subdomain. This process leads to a slow conformational transition in the albumins, makes the other binding sites of Co(II) exposed, and shows a positive cooperativity effect. The LMCT (ligand-to-metal charge transition) bands of the Co(II)-HSA and Co(II)-BSA systems also show a kind of hypochromic effect featuring a dipole-dipole interaction mechanism. This phenomenon is rarely reported.     

Study on the interaction between a water-soluble dinuclear nickel complex and bovine serum albumin by spectroscopic techniques

The interaction of a water-soluble dinuclear nickel(II) complex, [Ni₂(EGTB)(CH₃CN)₄](ClO₄)₄·4H₂O (EGTB = ethylene glycol-bis(β-aminoethyl ether) N,N,N′,N′-tetrakis(2-benzimidazoyl)) (1), and bovine serum albumin (BSA) was investigated under physiological conditions using fluorescence, synchronous fluorescence, UV–vis absorption and circular dichroism (CD). The experimental results suggested that the nickel(II) complex could bind to BSA with binding constant (K) ~ 10⁴ M^?1 and quench the intrinsic fluorescence of BSA through a static quenching mechanism. The thermodynamic parameters, ΔG°, ΔH°, and ΔS°, calculated at different temperatures, indicated that the binding reaction was spontaneous and electrostatic interactions played a major role in this association. Based on the number of binding sites, it was considered that one molecule of complex 1 could bind to a single site or two sites of the BSA molecule or the two binding modes coexisted. In view of the results of site marker competition experiments, the reactive sites of BSA to complex 1 mainly located in subdomain IIA (site I) and subdomain IIIA (site II) of BSA. Moreover, the binding distance, r, between donor (BSA) and acceptor (complex 1) was 5.13 nm according to Förster nonradiation energy transfer theory. Finally, as shown by the UV–vis absorption, synchronous fluorescence and CD, complex 1 could induce conformation and microenvironmental changes of BSA. The results obtained herein will be of biological significance in toxicology investigation and anticancer metallodrug design.