Molar Salt Concentrations Research Articles

Physicochemical changes in surimi with salt substitute

Protein endothermic transitions (thermal denaturation), rheological properties (protein gelation), and fundamental texture properties (shear stress and strain at mechanical fracture) of Alaska pollock surimi gels made with 0 (control), 1, 2, and 3g/100g of salt (NaCl) were determined and compared with equal molar concentration of salt substitute. Salt and salt substitute shifted the onset of myosin transition to higher temperature and resulted in larger myosin peaks (i.e., transition enthalpy). Endothermic transitions showed similar trends to rheological properties. The elastic modulus (G′) increased when salt or salt substitute was added to surimi, except at the highest concentration of salt and salt substitute. Salt and salt substitute also induced the onset of protein gelation (i.e., as measured by significant increase of G′) at lower temperature. Surimi gels with salt substitute and salt at equal molar concentrations had similar texture properties (shear stress and strain). Based on the present study, salt substitute can be used in the development of low-sodium surimi seafood products without significant change in gelation and texture.

Structural adaptation of extreme halophilic proteins through decrease of conserved hydrophobic contact surface

BackgroundHalophiles are extremophilic microorganisms growing optimally at high salt concentrations. There are two strategies used by halophiles to maintain proper osmotic pressure in their cytoplasm: accumulation of molar concentrations of potassium and chloride with extensive adaptation of the intracellular macromolecules ("salt-in" strategy) or biosynthesis and/or accumulation of organic osmotic solutes ("osmolyte" strategy). Our work was aimed at contributing to the understanding of the shared molecular mechanisms of protein haloadaptation through a detailed and systematic comparison of a sample of several three-dimensional structures of halophilic and non-halophilic proteins. Structural differences observed between the "salt-in" and the mesophilic homologous proteins were contrasted to those observed between the "osmolyte" and mesophilic pairs.ResultsThe results suggest that haloadaptation strategy in the presence of molar salt concentration, but not of osmolytes, necessitates a weakening of the hydrophobic interactions, in particular at the level of conserved hydrophobic contacts. Weakening of these interactions counterbalances their strengthening by the presence of salts in solution and may help the structure preventing aggregation and/or loss of function in hypersaline environments.ConclusionsConsidering the significant increase of biotechnology applications of halophiles, the understanding of halophilicity can provide the theoretical basis for the engineering of proteins of great interest because stable at concentrations of salts that cause the denaturation or aggregation of the majority of macromolecules.

Effect of silver ions coordination on morphology and performance of PES/PVP composite membrane in facilitated transport of ethylene

Structural and permeation properties of PES/PVP electrolyte composite membranes including association and dissociation behavior of silver nitrate salt within the polymer structure, structural situation of electron donor groups of membranes, surface and structural charge of membranes, crystalline variation of membrane active layer before and after salt addition and permeation properties of these membranes at different pressures including low pressures were evaluated. Structural evaluation through FTIR analysis revealed that the distributional condition of carrier agents is affected by increasing the AgNO 3 concentration. The efficiency of carriers for ethylene transportation is decreased by salt addition at molar concentrations more than 25%. However, according to the results obtained from zeta potential experiment, increasing the salt concentration enhances the surface and structure charge of membranes. Due to the salt crystals formation, the ascending trend of active layer crystallinity stopped at a salt molar concentration more than 25%. These physical and chemical reactions in the active layer structure caused the ethylene selectivity of final membranes to decrease at a salt molar concentration being more than 25%. The separation efficiency of a membrane with the AgNO 3 concentration of 25% was the most efficient situation. Adding a very thin and flexible PDMS layer on the surface of PES/PVP membrane in order to increase the real and ideal ethylene selectivity in the separation process was effective. Moreover, blending AgBF 4 and AgNO 3 salts was a new method for selectivity increament, which was applied in this research.

Gas vesicles isolated from Halobacterium cells by lysis in hypotonic solution are structurally weakened

Analysis of pressure-collapse curves of Halobacterium cells containing gas vesicles and of gas vesicles released from such cells by hypotonic lysis shows that the isolated gas vesicles are considerably weaker than those present within the cells: their mean critical collapse pressure was around 0.049–0.058 MPa, as compared to 0.082–0.095 MPa for intact cells. The hypotonic lysis procedure, which is widely used for the isolation of gas vesicles from members of the Halobacteriaceae, thus damages the mechanical properties of the vesicles. The phenomenon can possibly be attributed to the loss of one or more structural gas vesicle proteins such as GvpC, the protein that strengthens the vesicles built of GvpA subunits: Halobacterium GvpC is a highly acidic, typically “halophilic” protein, expected to denature in the absence of molar concentrations of salt.

Membrane Binding of Ribosomes Occurs at SecYE-based Sites in the Archaea Haloferax volcanii

Whereas ribosomes bind to membranes at eukaryal Sec61αβγ and bacterial SecYEG sites, ribosomal membrane binding has yet to be studied in Archaea. Accordingly, functional ribosomes and inverted membrane vesicles were prepared from the halophilic archaea Haloferax volcanii. The ability of the ribosomes to bind to the membranes was determined using a flotation approach. Proteolytic pretreatment of the vesicles, as well as quantitative analyses, revealed the existence of a proteinaceous ribosome receptor, with the affinity of binding being comparable to that found in Eukarya and Bacteria. Inverted membrane vesicles prepared from cells expressing chimeras of SecE or SecY fused to a cytoplasmically oriented cellulose-binding domain displayed reduced ribosome binding due to steric hindrance. Pretreatment with cellulose drastically reduced ribosome binding to chimera-containing but not wild-type vesicles. Thus, as in Eukarya and Bacteria, ribosome binding in Archaea occurs at Sec-based sites. However, unlike the situation in the other domains of Life, ribosome binding in haloarchaea requires molar concentrations of salt. Structural information on ribosome–Sec complexes may provide insight into this high salt-dependent binding.

Modelling of 3‐D Linear Viscoelastic Swelling of Charged Tissues and Gels

AbstractThe skeleton of hydrated tissues or gels exhibits flow‐independent viscoelastic properties [2] which are strongly coupled with the dissipative phenomena resulting from the interstitial fluid flow and the electrochemical swelling mechanisms [4]. Following this, it is the goal of this contribution to combine a linear viscoelasticity formulation with an electrochemical swelling theory in the framework of a well‐founded multiphasic concept. Proceeding from a macroscopic mixture approach, the governing equations can be expressed in terms of three primary variables, namely the solid displacement uS, the effective pore‐fluid pressure p and the molar salt concentration cm of the interstitial fluid.

Solvent interactions of halophilic malate dehydrogenase.

Malate dehydrogenase from the extreme halophilic Haloarcula marismortui (Hm MalDH) is an acidic protein that is unstable below molar salt concentrations. The solvated folded protein was studied by small-angle neutron scattering in solvents containing salt: NaCl, NaCH(3)CO(2), KF, NH(4)Cl, NH(4)CH(3)CO(2), (NH(4))(2)SO(4), MgCl(2), and MgSO(4). It was found that the global solvent interactions depend mainly on the nature of the cation. Complementary mass density measurements in MgCl(2), NaCl, NaCH(3)CO(2), and (NH(4))(2)SO(4) allowed determining the partial molal volumes of the protein, which were found to increase slightly with the salt, and the preferential salt binding parameters for each solvent condition. These are strongly dependent on the cation type and salt concentration. Hm MalDH can be modeled as an invariant particle binding 4100 water molecules in MgCl(2) and 2000 +/- 200 in NaCl, NaCH(3)CO(2), or (NH(4))(2)SO(4). The number of salt molecules associated to the particle decreases from about 85 to 0 in the order MgCl(2) > NaCl = NaCH(3)CO(2) > (NH(4))(2)SO(4). Alternatively, we considered exchangeable sites for water and salt with the effects of solvent nonideality. It does not change the description of the solvent interactions. Solvent anions act on Hm MalDH stability through a limited number of strong binding sites, as those seen at the interfaces of Hm MalDH by crystallography. Cations would act through some strong and numerous weak binding sites defined on the folded protein, in possible addition to nonspecific hydration effects.

Ionic Conductivity and Electrochemical Stability of Poly[oligo(ethylene glycol)oxalate]−Lithium Salt Complexes

A new series of highly conducting polymer electrolytes based on poly[oligo(ethylene glycol)oxalate], P(EGnO) where n represents the number of repeating ethyleneoxy unit, has been prepared. The dielectric constant of the polymer host is higher than that of the pure poly(ethylene oxide) due to the existence of the two carbonyl groups in the repeating unit. A maximum conductivity of 5.9 × 10-5 S cm-1 at 25 °C was obtained for the complex of LiTFSI and P(EG23O) with a molar salt concentration of [Li+]/[EO] = 1:16. The complexes also show good electrochemical stability up to 4.4 V versus Li+/Li.

The Boundary for Growth of Zygosaccharomyces bailii in Acidified Products Described by Models for Time to Growth and Probability of Growth

Models to predict days to growth and probability of growth of Zygosaccharomyces bailii in high-acid foods were developed, and the equations are presented here. The models were constructed from measurements of growth of Z. bailii using automated turbidimetry over a 29-day period at various pH, NaCl, fructose, and acetic acid levels. Statistical analyses were carried out using Statistical Analysis Systems LIFEREG procedures, and the data were fitted to log-logistic models. Model 1 predicts days to growth based on two factors, combined molar concentration of salt plus sugar and undissociated acetic acid. This model allows a growth/no-growth boundary to be visualized. The boundary is comparable with that established by G. Tuynenburg Muys (Process Biochem. 6:25–28, 1971), which still forms the basis of industry assumptions about the stability of acidic foods. Model 2 predicts days to growth based on the four independent factors of salt, sugar, acetic acid, and pH levels and is, therefore, much more useful for product development. Validation data derived from challenge studies in retail products from the U.S. market are presented for Model 2, showing that the model gives reliable, fail-safe predictions and is suitable for use in predicting growth responses of Z. bailii in high-acid foods. Model 3 predicts probability of growth of Z. bailii in 29 days. This model is most useful for spoilage risk assessment. All three models showed good agreement between predictions and observed values for the underlying data.

Antitumor bisdioxopiperazines inhibit yeast DNA topoisomerase II by trapping the enzyme in the form of a closed protein clamp.

The mechanism of inhibition of eukaryotic DNA topoisomerase II [DNA topoisomerase (ATP-hydrolyzing), EC 5.99.1.3] by a member of the bisdioxopiperazine family of anticancer drugs, ICRF-193, was investigated by using purified yeast DNA topoisomerase II. In the absence of ATP, ICRF-193 has little effect on the binding of the enzyme to various forms of DNA. In the presence of ATP, the drug converts the enzyme to a form incapable of binding circular DNA. Incubation of a preformed circular DNA-enzyme complex with ICRF-193 and ATP converts the complex to a form stable in molar concentrations of salt. These results can be interpreted in terms of the ATP-modulated protein-clamp model of type II DNA topoisomerases [Roca, J. & Wang, J. C. (1992) Cell 71, 833-840]; ICRF-193 can bind to the closed-clamp form of the enzyme and prevents its conversion to the open-clamp form. This interpretation is further supported by the finding that whereas both ATP and the drug are needed to form the salt-stable circular DNA-enzyme complex, ATP is not needed for maintaining this complex; furthermore, a signature of the closed-clamp form of the enzyme, Staphylococcus aureus strain V8 endoproteinase cleavage site at Glu-680, is observed if the enzyme is incubated with both ATP and ICRF-193. Inhibition of interconversion between the open- and closed-clamp forms of type II DNA topoisomerases offers a new mechanism in the selection and design of therapeutics targeting this class of enzymes.

Anion binding to the Schiff base of the bacteriorhodopsin mutants Asp-85—-Asn/Asp-212—-Asn and Arg-82—-Gln/Asp-85—-Asn/Asp-212—-Asn.

Studies of bacteriorhodopsin have indicated that the charge environment of the protonated Schiff base consists of residues Asp-85, Asp-212, and Arg-82. As shown recently (Marti, T., Rösselet, S. J., Otto, H., Heyn, M. P., and Khorana, H. G. (1991) J. Biol. Chem. 266, 18674-18683), in the double mutant Asp-85----Asn/Asp-212----Asn chromophore formation is restored in the presence of salts, suggesting that exogenous anions function as counterions to the protonated Schiff base. To investigate the role of Arg-82 and of the Schiff base in anion binding, we have prepared the triple mutant Arg-82----Gln/Asp-85----Asn/Asp-212----Asn and compared its properties with those of the Asp-85----Asn/Asp-212----Asn double mutant. Regeneration of the chromophore with absorption maximum near 560 nm occurs in the triple mutant in the presence of millimolar salt, whereas in the double mutant molar salt concentrations are required. Spectrometric titrations reveal that the pKa of Schiff base deprotonation is markedly reduced from 11.3 for the wild type to 4.9 for the triple mutant in 1 mM NaCl and to 5.5 for the double mutant in 10 mM NaCl. In both mutants, increasing the chloride concentration promotes protonation of the chromophore and results in a continuous rise of the Schiff base pKa, yielding a value of 8.4 and 7.6, respectively, in 4 M NaCl. The absorption maximum of the two mutants shows a progressive red shift, as the ionic radius of the halide increases in the sequence fluoride, chloride, bromide, and iodide. An identical spectral correlation in the presence of halides is observed for the acid-purple form of bacteriorhodopsin. We conclude, therefore, that upon neutralization of the two counterions Asp-85 and Asp-212 by mutation or by protonation at low pH, exogenous anions substitute as counterions by directly binding to the protonated Schiff base. This interaction may provide the basis for the proposed anion translocation by the acid-purple form of bacteriorhodopsin as well as by the related halorhodopsin.

The group IIB intron from the green alga Scenedesmus obliquus mitochondrion: molecular characterization of the in vitro splicing products

In the presence of high molar salt concentrations, the mitochondrial group IIB intron (rI1) from the green alga Scenedesmus obliquus is capable of splicing in vitro. After establishing the optimal conditions for RNA processing the in vitro splicing products were unequivocally identified in self-splicing experiments by Northern hybridization analysis employing 3'end-labelled RNAs or exon- and/or intron-specific probes. Finally, two trans-esterification products were identified by sequencing of the spliced RNA. From our data we conclude that the processing of group II introns from both algal and yeast mitochondria is preceded by identical consecutive trans-esterification steps. The predicted secondary and tertiary structure of intron rI1 of S. obliquus contains all the motifs necessary for optimal self-splicing and which are characteristic of other group IIB introns from different species.

The Influence of Inorganic Salts on the Inhibition of Acetylcholinesterase by O,O-Diethylthiophosphates

Abstract The influence of various inorganic salts (NaCl, KCl, CsCl, KNO3, Na2SO4, K2SO4, MgCl2, CaCl2) on the kinetics of the reactions of acetylcholinesterase with neutral and cationic 0,O-diethylthiophosphates, (C2H50)2 P(0)SX, where × = (CH2)n and (CH2)n S+ (CH3) C2H5 (n=1–6), has been studied at 25° C and pH 7.5. The salt effect in the second-order rate constant can be quantitatively described by the equation log(k2/Ks) = log(k2 /KS)°-ψlog[M] + bc where bc is the term for the kinetic salting effect, ψlog[M] is the electrostatic term, c and [MI are the molar concentrations of salt and salt cation. The salting effect is observed in the binding step (Ks) as well as in the enzyme phosphorylation step (k2). Parallel increase of b with increasing n has been observed for the series of both ionic and neutral inhibitors. Electrostatic effect is observed only in the binding step for cationic inhibitors and does not depend on the distance between the onium atom and the reaction center in the inhibitor molecule. The observation of uniform Y is in accordance with the Manning's polyelectrolyte theory, suggesting that acetylcholinesterase can be considered as negatively charged polyelectrolyte. According to the theory the release of condensed counterions from the polyelectrolyte provides electrostatic contribution to the binding of cationic ligands, and the presence of localized anionic site on the acetylcholinesterase molecule is not required to account for the observed electrostatic effect. The obtained mean value of ψ = 0.49 ± 0.08 can be used as a quantitative parameter to characterize the effective charge density of acetylcholinesterase.

EROSION OF COHESIVE SOILS

Experiments on erosion of cohesive soils using a circular couette flow erosion device and three clays with eight electrolytes (solutions) at approximately constant temperature are described. The analysis of the experimental results using the erosion model based on the rate process concept shows that the erosion rate of a clay by an electrolyte with different pH-values and molar salt concentrations can be explained by the orientation of the clay aggregates in the slurries before consolidation as well as predicted. The features of the eroded clay surfaces depend on the nature of the clay. The eroded surfaces of stiffer clays look in scanning microscope pictures distinctly pitted, whereas surfaces of clays with face to face stacking appear to flake. The eroded surfaces of soft clays show moulded features and undulating surface forms. However, most of the clays are neither stacked face to face nor soft, and they show an intermediate form of eroded surface features. Except for very soft clay, the surface of th...

Soluble pig intestinal cell membrane components with affinities for E. coli K88+ antigen.

Pig intestinal brush borders (BB) were radiolabeled by iodination using the lactoperoxidase-hydrogen peroxide procedure. The BB were then detergent solubilized, centrifuged to remove particulate material, and chromatographed on Sepharose CL-4B. The fractions were incubated with K88+ E. coli using an in vitro binding assay. Binding of the iodinated membranes to K88+ E. coli occurred throughout a wide range of molecular weight components, in excess of 690K daltons to near 25K daltons. The system utilizing intact K88+ E. coli and solubilized BB was shown to be saturable. Prior contact of K88+ E. coli with nonradiolabeled membranes or specific antibodies to K88+ pili inhibited binding of the radiolabeled BB. Simple sugars were tested for their ability to block binding of the labeled BB; partial inhibition occurred with galactose (17.9%), galactosamine (32%), glucose (10.6%), and N-acetylglucosamine (32%). Calcium enhanced binding with as little as 10 microM. A 10 x increase in binding occurred with 500 microM calcium. Affinity chromatography using K88+ pili coupled on agarose beads avidly bound the labeled BB. The receptor membranes were eluted with high molar concentrations of salt, however considerable degradation occurred. Despite low yields from the affinity system, receptor membranes with higher binding activities were recovered. Protein: glycoprotein ratios were 1:4. Elution with SDS and electrophoresis on 12.5% polyacrylamide gels in the presence of a reducing agent produced two major subunits 35--32K and 23K daltons. These components were recovered from the gels and retained their binding activity. This information suggests that the intestinal receptor responsible for binding of K88+ E. coli is a glycoprotein, that in the native state exists in multimeric forms.

Effects of inorganic salts on the properties of aqueous poly(ethylene oxide) solutions

AbstractCloud‐point curves have been determined for aqueous solutions of poly(ethylene oxide) (PEO) at several concentrations for a variety of inorganic salts (sulfates, carbonates, nitrates, and chlorides). From these, theta conditions have been determined. The resulting dependences of the critical temperature θ (mostly between 300 and 360°K) on the molar concentrations (or ionic strengths) of the salts in solution cannot wholly be summarized in sequences of ion effects. The major findings are that sulfates and carbonates are much more effective in reducing θ than the chlorides and nitrates at the same concentrations. The trends found depend on salt concentration, i.e., certain plots of the data cross over, but they broadly agree with those found for comparable systems by other workers. Exceptional are the chlorides of Group II and LiCl which show minima when θ is plotted against molar salt concentration. While interpretations based on solvent structure‐breaking are not adequate, there are similarities in behavior with the structure‐breaking attributes of the ions based on independent studies (infrared). The results are briefly discussed in terms of current postulates: a more detailed discussion will accompany further experimental studies on these systems.

The Solubilities of Hydrocarbons in Concentrated Salt Solutions and Their Correlation with the Clathrate Water Theory, Ion-Ion Associations, and Structures of Polymers

Abstract The solubility of benzene, benzoic acid, and hexanol in aqueous solutions containing various salts or dipolar molecules was examined. Both the anion and cation of guanidinium or other salts determines the salting-in properties. The solubility of benzene was found to be a linear function of the molar concentration of salt, CS, to the saturation point of the salt; i.e., the solubility constant kS remains the same. In other words, the interaction of benzene with hydrated ions is the same at extremely low ionic strengths as at high ionic strengths. This result agrees with the proposal that the B region (or negatively hydrated region) of ions consists of a single monomolecular layer of water molecules. Moreover, since in such concentrated salt solutions all water molecules are hydrated, the disappearance of any proposed clathrate structure in concentrated salt solutions should alter the value of kS. Consequently, the constant kS values show that water clathrate structures do not surround hydrocarbons....

Selective inhibition of elastolytic and proteolytic properties of elastase

The elastolytic and proteolytic (fibrin, casein, and hemoglobin) properties of elastase, purified by CM-cellulose chromatography and electrophoretically homogeneous at pH's 9.0 and 4.5, could be selectively inhibited. Soybean trypsin inhibitor and kallikrein inactivator substantially suppressed proteolytic activity of the enzyme, but were without influence on its elastolytic properties. Conversely, elastolysis was substantially suppressed by high molar salt concentration, whereas proteolysis was not influenced thereby. These results suggest either the presence of several enzymes with similar chromatographic and electrophorctic properties, or else that elastase has more than one active center, one directed against as yet unspecified regions or linkages of elastin, the other having broad and more classical proteolytic properties.

THE EFFECT OF SALTS ON THE IONISATION OF GELATIN

The effect of the addition of sodium chloride to gelatin solutions is shown from the Donnan relationship to increase the ionisation of the gelatin, the increase produced in acid solutions reaching a maximum at about 1/1000 molar salt concentration. This effect is attributed to the formation of complex ions. From the similar action of calcium and copper chlorides the effective combining power of gelatin for complex positive ion formation is deduced. The bearing of complex ion formation on the zwitter-ionic structure and solubility phenomena of proteins is pointed out.

Effect of electrolytes on the rate of inactivation of bacteriophage during precipitation.

In view of the ease with which the bacteriophage principle is adsorbed, it is in the majority of instances carried down in the sediment when lytic filtrates are caused to precipitate. In certain cases the lytic agent remains active in the sediment and can be recovered by solution of the latter, and in other cases after adsorption it becomes inactive. For instance, if lytic filtrate, as ordinarily prepared, is precipitated by an excess of acetone, the bacteriophage can be recovered from the precipitate. However, if the NaCl concentration of the filtrate is increased to 1 per cent or over, 99 per cent of the phage is lost within a short time after the addition of acetone. The inactivating effect of salts with divalent cations is even more pronounced, and in certain instances, even 0.05 molar concentration of salt produces rapid and complete inactivation of lytic agent, when acetone is added. If salts with monovalent and divalent cations are mixed in suitable proportions, they antagonize one another in producing this effect. Similar antagonistic effect of salts is observed also in the case of alcohol precipitation of the bacteriophage. Thus, if a small amount of CaCl2 is added to a lytic filtrate, as ordinarily prepared, it becomes considerably less subject to injury by the alcohol, in virtue of the fact that the effect of the NaCl contained in the filtrate is diminished by the addition of CaCl2.