Effect Of Monovalent Salts Research Articles

Unfolding/refolding of single polyproteins held under constant tension: Effect of monovalent salts on folding/unfolding rates

Protein elasticity is a fundamental physical characteristic and, in some cases, a key functional property of proteins. Many proteins consist of tandem repeats of identical or similar domains and display an elasticity that is dependent on the folding/unfolding of their individual domains. These proteins allow for extreme extensions beyond their resting length with distinct, stepped increases/decreases in length when held under ramped or constant tensions. Here we present the extension of a poly-protein consisting of 8 tandem repeats of Protein L held under constant tension utilizing a magnetic tweezers technique. We present a model of the observed results employing a simple two-state model for the unfolding of each domain. The model includes the polymer elasticity of the entire chain and incorporates the indistinguishability of the Protein L domains. From this model, we have estimated the change in energy for the unfolding of a single Protein L as 6.5 kT. Further, we explored the dependency of folding/unfolding rates under tension on environmental salt concentration. We have found that increases in NaCl concentration tend to increase the transition rates between states of unfolding without much perturbation to the probability of being in a given unfolded state, implying a lowering of the barrier to protein folding/unfolding in protein L due to excess environmental salts.

Effect of monovalent salts on molecular interactions of globular protein (BSA) above its isoelectric point

Protein-protein interactions study is crucial for understanding functions of proteins in the living system. Here, the molecular interactions of bovine serum albumin (BSA) with the addition of different monovalent (Li+, Na+, and K+) and one divalent (Mg2+) cations were studied above the isoelectric point of the protein. Small-angle neutron scattering study reveals that though short-range attractive interactions remain unchanged, long-range repulsion strength decreases with increasing ion concentration. The presence of ions and variation of their concentration also affect the diffusion coefficient of protein. The protein-protein interactions are ion-specific and modified according to the charge density of the cations.

Effects of Monovalent Salt on Protein-Protein Interactions of Dilute and Concentrated Monoclonal Antibody Formulations.

In this study, we used sodium chloride (NaCl) to extensively modulate non-specific protein-protein interactions (PPI) of a humanized anti-streptavidin monoclonal antibody class 2 molecule (ASA-IgG2). The changes in PPI with varying NaCl (CNaCl) and monoclonal antibody (mAb) concentration (CmAb) were assessed using the diffusion interaction parameter kD and second virial coefficient B22 measured from solutions with low to moderate CmAb. The effective structure factor S(q)eff measured from concentrated mAb solutions using small-angle X-ray and neutron scattering (SAXS/SANS) was also used to characterize the PPI. Our results found that the nature of net PPI changed not only with CNaCl, but also with increasing CmAb. As a result, parameters measured from dilute and concentrated mAb samples could lead to different predictions on the stability of mAb formulations. We also compared experimentally determined viscosity results with those predicted from interaction parameters, including kD and S(q)eff. The lack of a clear correlation between interaction parameters and measured viscosity values indicates that the relationship between viscosity and PPI is concentration-dependent. Collectively, the behavior of flexible mAb molecules in concentrated solutions may not be correctly predicted using models where proteins are considered to be uniform colloid particles defined by parameters derived from low CmAb.

Effects of Monovalent Salt on Ether-Linked Phospholipid Bilayers

Effects of Monovalent Salt on Ether-Linked Phospholipid Bilayers

Tuning Colloidal Stability of Layered Double Hydroxides: From Monovalent Ions to Polyelectrolytes.

The growing number of applications of layered double hydroxide (LDH) colloids demands for detailed understanding of particle aggregation processes in such samples. Tuning the colloidal stability in aqueous suspensions is essential to design stable systems or to induce controlled aggregation of these elongated particles. In this review, recent progress in this field is summarized; in particular, the charging and aggregation of LDHs of various compositions and sizes in the presence of different aggregating agents are discussed. The review focuses on the effect of monovalent salts, multivalent ions, and polyelectrolytes on the suspension stability of LDHs. The provided information will help to better understand the origin of interparticle forces responsible for the colloidal stability and to design highly stable or aggregating LDH colloids according to the desired goals in certain applications. Moreover, potential future research directions to obtain a broader picture of LDH aggregation are also suggested.

Effect of lithium salts on lactate dehydrogenase, adenylate kinase, and 1-phosphofructokinase activities

Inhibitions of 30 nM rabbit muscle 1-phosphofructokinase (PFK-1) by lithium, potassium, and sodium salts showed inhibition or not depending upon the anion present. Generally, potassium salts were more potent inhibitors than sodium salts; the extent of inhibition by lithium salts also varied with the anion. Li2CO3 was a relatively potent inhibitor of PFK-1 but LiCl and lithium acetate were not. Our results suggest that extents of inhibition by monovalent salts were due to both cations and anions, and the latter needs to be considered before inhibition can be credited to the cation. An explanation for monovalent salt inhibitions is proffered involving interactions of both cations and anions at negative and positive sites of PFK-1 that affect enzyme activity. Our studies suggest that lithium cations per se are not inhibitors: the inhibitors are the lithium salts, and we suggest that in vitro studies involving the effects of monovalent salts on enzymes should involve more than one anion.

Hofmeister Effects of Common Monovalent Salts on the Beetle Antifreeze Protein Activity

Antifreeze proteins (AFPs) noncolligatively depress the freezing point of a solution and produce a difference between the melting and freezing points termed thermal hysteresis (TH). While the mechanism of the enhancement effect is not well understood, various low-molecular-mass solutes including neutral salts have been identified to enhance the TH activities of AFPs. Here, the effect of monovalent salts on salting out an AFP from the beetle Dendroides canadensis (DAFP-1) on the ice was treated using a simple classical theory, and the relationship between the TH activity and the salt concentration was developed. The TH activities of DAFP-1 in the presence of the series of monovalent salts were assessed by differential scanning calorimetry (DSC), and the salting-out constants of DAFP-1 by these salts were determined. This study demonstrates an indirect way to determine the salting-out constants of AFPs by these salts. The results suggest that the Hofmeister effect is a potential mechanism for the TH enhancement effects of some common monovalent salts.

Effects of salts in the Hofmeister series and solvent isotopes on the gelation mechanisms for hydroxypropylmethylcellulose hydrogels

AbstractThe effects of various inorganic salts and isotopic solvents on the thermal gelation behavior of hydroxypropylmethylcellulose (HPMC) in aqueous solutions were examined by micro‐differential scanning calorimetry and rheological measurements. It was found that salting‐out salts, such as NaCl, promoted the sol–gel transition of HPMC at a lower temperature. An analysis of solvent isotope effects on the changes in the temperature at maximum heat capacity (Tm) with salt concentration showed that interchain hydrogen bonding (hydrogen bonding between the hydroxyl groups of different HPMC chains) was involved in the sol–gel transition, and its strength depended on the temperature and salt concentration. It was demonstrated that the effectiveness of anionic species in changing the Tm of the HPMC solutions was in the sequence of the Hofmeister series. Anionic species play a role in reducing Tm by their influence on the structure of the water, which in turn affects interactions between hydroxyl groups and water molecules, interchain hydrogen bonding, and the strength of the water cages prohibiting hydrophobic association. Rheological and microcalorimetric results indicated that the change in the thermodynamics of gelation of the HPMC aqueous solution was determined by the salt types and concentration, and the effect of monovalent salts was found to be more cooperative than that of multivalent salts on the sol–gel transition. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Dynamic Analysis and Optimization of Surfactant Dosage in Micellar Enhanced Ultrafiltration of Nickel from Aqueous Streams

The micellar enhanced ultrafiltration of Ni(II) ions from the aqueous solution was studied for the dead end system using 20KD Polysulfone membrane. Dynamic behavior of the system was studied with respect to the rejection, yield, and normalized flux. The effect of feed metal ion concentration, surfactant concentration, pH, transmembrane pressure, and S/M ratio was investigated and the optimization of S/M ratio was done. The optimum S/M ratio was 10 while the critical S/M ratio was 5. The effect of monovalent salts was studied on the rejection of metal ions for the salt concentration between 10 mM to 500 mM.

Effect of Monovalent Salt on Cationic Lipid Membranes As Revealed by Molecular Dynamics Simulations

An atomic-scale understanding of cationic lipid membranes is required for development of gene delivery agents based on cationic liposomes. To address this problem, we recently performed molecular dynamics (MD) simulations of mixed lipid membranes comprised of cationic dimyristoyltrimethylammonium propane (DMTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC) (Biophys. J. 2004, 86, 3461-3472). Given that salt ions are always present under physiological conditions, here we focus on the effects of monovalent salt (NaCl) on cationic (DMPC/DMTAP) membranes. Using atomistic MD simulations, we found that salt-induced changes in membranes depend strongly on their composition. When the DMTAP mole fraction is small (around 6%), the addition of monovalent salt leads to a considerable compression of the membrane and to a concurrent enhancement of the ordering of lipid acyl chains. That is accompanied by reorientation of phosphatidylcholine headgroups in the outward normal direction and slight changes in electrostatic properties. We attribute these changes to complexation of DMPC lipids with Na(+) ions which penetrate deep into the membrane and bind to the carbonyl region of the DMPC lipids. In contrast, at medium and high molar fractions of cationic DMTAP (50 and 75%) a substantial positive surface charge density of the membranes prevents the binding of Na(+) ions, making such membranes almost insensitive to monovalent salt. Finally, we compare our results to the Poisson-Boltzmann theory. With the exception of the immediate vicinity of the bilayer plane, we found excellent agreement with the theory. This is as expected since unlike in the theoretical description the surface is now structured due to its atomic scale nature.

Effect of monovalent salts on morphology of calcium carbonate crystallized in Couette‐Taylor reactor

AbstractMonovalent ionic additives, Na+, K+ and NH impact on the morphology and agglomeration of CaCO3 crystals. As increasing the additive concentration, the regular shaped crystals such as rhombohedron and spindle are changed to irregular one due to the inclusion of Na+ and K+ into the crystal structure. The inclusion of Na+ and K+ is detected using ICP‐AES. The partition of coefficients of Na+ and K+ are estimated as 9.74 × 10–4, 9.73×10–4, respectively and the amount of inclusion in the crystals is about 2×103 ppm. However, the inclusion of ions does not modify a crystal structure of calcite. Since NH4+ is large in radius, it is not included in crystal but shifts the spindle shape of crystal to the rhombohedral one. It is interesting to find that such modification of crystal morphology begins to appear at high additive concentration (0.05 M). In addition, the crystal agglomeration is promoted because the electric repulsive charge is reduced as increasing the additive concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Folding transition of DNA depending on ionic environments

We examined the effect of monovalent salts, NaCl and KCl, on spermidine-induced DNA compaction using fluorescence microscopy. By increasing concentrations of salts, unfolding process of compacted DNAs were observed. It was also shown that NaCl is more effective for unfolding compacted DNAs than KCl.

Interactions of silver colloids with phospholipid monolayers

Electrostatic interactions of silver colloids with phospholipid monolayers at the air- water interface have been investigated by pressure-area measurements and fluorescence microscopy observations. It has been observed that the presence of silver particles in the subphase induces a change in the compression isotherms of phosphatidylglycerol, in particular in liquid-expanded LE / liquid-condensed LC phase transition. Condensed-phase domains show fractal-like shapes over colloids-containing subphases in contrast with rounded shapes observed over pure water. The effect of colloids on the compressibility was studied for different chain lengths and the change of the critical temperature was also determined. The comparison with the effect of monovalent salt was discussed since the charged colloids could be viewed as "multivalent" ions.

Role of ionic species and valency on the viscoelastic properties of partially hydrolyzed polyacrylamide solutions

The effects of ionic species and valency on the viscoelastic properties of partially hydrolyzed polyacrylamide solutions were examined. Two viscoelastic parameters were considered, i.e., average relaxation time, λM0 and steady state compliance, Je0. Both these parameters are independent of ionic species of monovalent salts. However, λM0 decreases with increasing salt concentrations. Divalent salts reduce the values of λM0 by as much as 10 times. On the other hand, Je0 is independent of salt concentrations and valency. The effects of monovalent salt on three different polyacrylamide samples of varying degree of hydrolysis and MW were also examined.

Effect of cations on heat degradation of chelator-soluble carrot pectin

The effects of monovalent salts, NaCl, KCl, and NH 4Cl, and divalent salts, ZnCl 2, CaCl 2, SrCl 2, CdCl 2, and MgCl 2, on heat degradation of pectin at pH 6·1 were examined. The β-eliminative degradation of extracted carrot pectin increased as cation concentration in the pectin solution was raised. At the same level of pectin methoxyl content, divalent cations promoted more depolymerization during the heating of pectin than did monovalent cations. The enhancement effect of cations on pectin degradation was greater for low-methoxyl pectin than for high-methoxyl pectin. The enhancement effect of cations increased in the order Zn ++ > Ca ++ > Cd ++ ≈ Sr ++ > Mg ++ ≈ Na + ≈ K + > NH 4 +.

Rheology of Water-Soluble Polymers: A Comparative Study on the Effect of Monovalent Salt

Abstract A comparative study was conducted on three commercial water-soluble polymers: partially hydrolyzed polyacrylamide (Separan AP30—Dow Chemicals), polyethylene oxide (Polyox Coagulant—Union Carbide), and xanthan gum (Keltrol—Kelco). Both the steady shear and the dynamic properties were examined. The presence of salt significantly reduces the viscous and elastic properties of Separan AP30. Negligible changes were observed for Polyox Coagulant. However, some marginal reduction in these properties was evident for xanthan gum at low salt concentration up to cs of 0.05 M, beyond which no effect was observed. The relationship between the rheological properties of the polymers and the salt concentration is governed by the charged characteristics of the polymer chains. The present study suggests that it is more desirable to use xanthan gum than polyacrylamide in a high-salt environment. Polyethylene oxide is usually avoided due to its cost and low resistance to mechanical degradation.

Effect of charged amphiphiles on the stability of lamellar mesophases

The region of existence for a lamellar mesophase with low surface charge density is calculated using contributions from interbilayer dispersive, hydration, and electric double layer forces, together with mixing entropies. Also, the effect of monovalent salt is treated. Below a critical charge density, two lamellar mesophases are found to coexist in a limited water concentration interval. Previously published experimental evidence for this type of phase separation is discussed.

The effect of monovalent salts on the acceleration of myosin B ATPase by magnesium

The effects of magnesium and of calcium on the ATPase activity of myosin B have been investigated in the presence of a range of concentrations of monovalent salts ([Me +A −]). At zero or low [Me +A −] MgCl 2 increases the ATPase activity; at intermediary [Me +A −] low concentrations of MgCl 2 depress activity while high concentrations of MgCl 2 accelerate slightly; at high [Me +A −], high concentrations of MgCl 2 have a small accelerative tendency. The rise in activity at high [Me +A −] and the second rise at intermediate [Me +A −] are caused by 10 −3 M MgCl 2 and have not been observed in other investigations. The inhibition caused by magnesium is not clearly due to dissociation of myosin B into actin and myosin A. The effects of salts on the Mg-effect does not appear to be one of ionic strength because the kind of salt has an effect. The response of myosin B ATPase is inconsistent from preparation to preparation. Differences in myosin B preparations are shown. The possibility of covalent and electrostatic bonding of magnesium to myosin is discussed. The effects of magnesium on the ATPase of glycerol-extracted muscle are not as complex as on that of myosin B. Ammonium chloride in the absence of other metallic cations increases the activity of myosin B ATPase.