Interaction of Proteoglycans and Chondroitin Sulfates with Calcium or Phosphate Ions

1971 ◽  
Vol 49 (4) ◽  
pp. 417-425 ◽  
Author(s):  
E. A. MacGregor ◽  
J. M. Bowness
Keyword(s):  
Ionic Strength ◽  
Chondroitin Sulfate ◽  
Calcium Binding ◽  
Equilibrium Dialysis ◽  
Equilibrium System ◽  
Chondroitin Sulfates ◽  
Phosphate Ions ◽  
Wide Range ◽  
The Difference ◽  
Low Ionic Strength

Equilibrium dialysis was used to study the distribution of calcium or phosphate ions at equilibrium in dialysis cells containing proteoglycan or chondroitin sulfate in one compartment. A higher concentration of calcium or lower concentration of phosphate was found in the cell compartment containing the polymer than in the compartment separated from it by a semipermeable membrane. The difference in calcium concentration across the boundary represents bound calcium. The formation constant (K) for the complex of bound calcium with chondroitin sulfate was investigated and found to be affected by two main factors: ionic strength and calcium/glucuronate ratio. K decreased rapidly with increasing ionic strength up to 0.15. At low ionic strength and high Ca2+/glucuronate ratios, evidence has been obtained that more calcium is bound by the polymers than can be accounted for by the simple equilibrium system, involving the combination of one calcium per disaccharide unit period, whose operation is consistent with the K values found at low Ca/glucuronate ratios over a wide range of ionic strengths. Infrared spectra obtained at high and low Ca2+/glucuronate ratios also indicate the existence of two calcium forms of proteoglycans. Viscosity and ultracentrifugal data show that differences exist between proteoglycans in calcium and sodium solutions. The data for disaggregated proteoglycan preparations indicate that their calcium-binding properties are very similar to those of chondroitin 4-sulfate and are determined by the same factors. One aggregated puppy rib proteoglycan, however, showed significantly greater K values than chondroitin 4-sulfate; these decreased after disaggregation.

scholarly journals Some electron-transfer reactions involving carbodi-imide-modified cytochrome c

1987 ◽  
Vol 243 (2) ◽  
pp. 379-384 ◽  
Author(s):  
A J Mathews ◽  
T Brittain
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Protein Charge ◽  
Native Proteins ◽  
Wide Range ◽  
Internal Electron ◽  
Modified Proteins ◽  
Time Courses ◽  
Low Ionic Strength ◽  
Kinetics Of

The reaction kinetics of native and carbodi-imide-modified tuna and horse heart cytochromes c with both a strong (dithionite) and a relatively weak (ascorbate) reducing agent were studied over a wide range of conditions. In their reactions with dithionite both the native and modified cytochromes exhibit single exponential time courses. The effects of dithionite concentration and ionic strength on the rate of the reduction are complex and can best be explained in terms of the model proposed by Lambeth & Palmer [(1973) J. Biol. Chem. 248, 6095-6103]. According to this model, at low ionic strength the native proteins are reduced almost exclusively by S2O4(2-) whereas the modified proteins showed reactivity towards both S2O4(2-) and SO2.-. These findings are interpreted in terms of the different charge characteristics of the carbodi-imide-modified proteins relative to the native proteins. The findings that the modified proteins react with ascorbate in a biphasic manner are explained as arising from ascorbate binding to a reducible form of the protein, before electron transfer, with an equilibrium between the ascorbate-reducible form of the protein and a non-reducible form. Estimates were obtained for both the ascorbate equilibrium binding constant and the rate constant for the internal electron transfer for both the native and modified horse and tuna proteins. The effect of pH on the reactions indicates that the active reductant in all cases is ascorbate2-. The studies of ascorbate reactivity yield important information concerning the proposed correlation between ascorbate reducibility and the presence of a 695 nm-absorption band, and the study of dithionite reactivity illustrates the effect of protein charge and solution ionic strength on the relative contributions made by the species SO2.- and S2O4(2-) to the reduction of ferricytochrome c.

Ionic strength- and pH-dependence of calcium binding by terrestrial humic acids

2012 ◽  
Vol 9 (1) ◽  
pp. 89 ◽  
Author(s):  
Iso Christl
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Humic Acids ◽  
Calcium Binding ◽  
Good Description ◽  
Ph Dependence ◽  
Wide Range ◽  
Electrostatic Binding ◽  
Carboxylic Groups ◽  
Terrestrial Environments

Environmental contextIn terrestrial environments, humic substances act as major sorbents for calcium, which is an essential nutrient for organisms. This study shows that calcium binding by terrestrial humic acids is strongly dependent on pH and ionic strength. The results indicate that calcium binding by humic acids is primarily controlled by electrostatic forces and specific binding to carboxylic groups. AbstractCalcium binding by two terrestrial humic acids was investigated at 25 °C as a function of pH, ionic strength and Ca2+ activity with calcium titration experiments. A Ca2+-selective electrode was used for Ca2+ measurements to cover a wide range of Ca2+ activities (10–8.5–10–2.5). Experimental data were quantitatively described with the NICA–Donnan model accounting for electrostatic and specific calcium binding. The results showed that calcium binding as a function of Ca2+ activity was strongly affected by variations of pH and ionic strength indicating that electrostatic binding is an important mechanism for calcium binding by humic acids. Data modelling providing a good description of experimental data for both humic acids suggested that electrostatic binding was the dominant calcium binding mechanisms at high Ca2+ activities often observed in terrestrial environments. Specific calcium binding being quantitatively predominant only at low Ca2+ activities was exclusively attributed to binding sites exhibiting a weak affinity for protons considered to represent mainly carboxylic groups. Since the negative charge of the humic acids being prerequisite for electrostatic calcium binding was found to be mainly due to deprotonation of carboxylic groups except under alkaline conditions, carboxylic groups were identified to primarily control calcium binding of humic acids.

scholarly journals Role of the reticulum in the stability and shape of the isolated human erythrocyte membrane

1982 ◽  
Vol 92 (3) ◽  
pp. 714-721 ◽  
Author(s):  
Y Lange ◽  
RA Hadesman ◽  
TL Steck
Keyword(s):  
Ionic Strength ◽  
Erythrocyte Membrane ◽  
Human Erythrocyte ◽  
Time Course ◽  
Isotonic Saline ◽  
Human Erythrocyte Membrane ◽  
Wide Range ◽  
Cell Stability ◽  
Mechanically Stabilized ◽  
Low Ionic Strength

In order to examine the widely held hypothesis that the reticulum of proteins which covers the cytoplamsic surface of the human erythrocyte membrane controls cell stability and shape, we have assessed some of its properties. The reticulum, freed of the bilayer by extraction with Triton X-100, was found to be mechanically stable at physiological ionic strength but physically unstable at low ionic strength. The reticulum broke down after a characteristic lag period which decreased 500-fold between 0 degrees and 37 degrees C. The release of polypeptide band 4.1 from the reticulum preceded that of spectrin and actin, suggesting that band 4.1 might stabilize the ensemble but is not essential to its integrity. The time-course of breakdown was similar for ghosts, the reticulum inside of ghosts, and the isolated reticulum. However, at very low ionic strength, the reticulum was less stable within the ghost than when free; at higher ionic strength, the reverse was true. Over a wide range of conditions the membrane broke down to vesicles just as the reticulum disintegrated, presumably because the bilayer was mechanically stabilized by this network. The volume of both ghosts and naked reticula varied inversely and reversibly with ionic strength. The volume of the naked reticulum varied far more widely than the ghost, suggesting that its deformation was normally limited by the less extensible bilayer. The contour of the isolated reticulum was discoid and often dimpled or indented, as visualized in the fluorescence microscope after labeling of the ghosts with fluoroscein isothiocyanate. Reticula derived from ghosts which had lost the ability to crenate in isotonic saline were shriveled, even though the bilayer was smooth and expanded. Conversly, ghosts crenated by dinitrophenol yielded smooth, expanded reticula. We conclude that the reticulum is a durable, flexible, and elastic network which assumes and stabilizes the contour of the membrane but is not responsible for its crenation.

The binding of Zinc by S-Carboxymethyl Kerateine 2 from wool

1957 ◽  
Vol 10 (3) ◽  
pp. 344 ◽  
Author(s):  
JM Gillespie ◽  
PH Springell
Keyword(s):  
Ionic Strength ◽  
Chelating Agents ◽  
Zinc Concentration ◽  
Equilibrium Dialysis ◽  
Acetate Solution ◽  
Free Zinc ◽  
Zinc Acetate Solution ◽  
The Difference ◽  
Protein Components ◽  
Ph Range

The binding of zinc from zinc acetate solution by the S-carboxymethyl derivative of kerateine 2 (SCMK2), a soluble protein extracted from reduced wool, has been studied by the method of equilibrium dialysis over the pH range 5.5 to 8.0 using radioactive 65Zn to determine the zinc concentration. The binding increases as the pH increases from 5.5 to 7.5. The extent of binding is also a function of free zinc concentration, but it is not affected by changes in ionic strength between 0.15 and 1.0. The difference in solubility between the zinc complexes of the two protein components of SCMK2 is probably not due to the differences in the amount of zinc bound. The binding of zinc is reversible over the concentration range studied at both pH 6.0 and 7.5, and its removal is accelerated by treatment with chelating agents. Over the pH range 6.0 to 7.5 more zinc is bound by this protein than can be accounted for by histidine binding alone, assuming a 1 : 1 zinc-histidine ratio.

scholarly journals ATP, uncomplexed by divalent cations, and the LC2 light chain are interdependent modifiers of the skeletal actomyosin MgATPase activity

1991 ◽  
Vol 280 (1) ◽  
pp. 39-44
Author(s):  
S M Pemrick ◽  
P A Martinez
Keyword(s):  
Ionic Strength ◽  
Light Chain ◽  
Divalent Cations ◽  
High Ionic Strength ◽  
Negative Effects ◽  
Thin Filament Regulation ◽  
Skeletal Muscle Contraction ◽  
Wide Range ◽  
Low Ionic Strength ◽  
Mgatpase Activity

In the absence of troponin and tropomyosin, skeletal actomyosin MgATPase activity can be altered by 2-3-fold by divalent cations. The ‘sign’ of this effect (i.e. inhibition or activation) varies with ionic strength. To investigate the mechanism, P(i) liberation was analysed at both low and high ionic strength with three concentrations of MgATP and over a wide range of Mg2+ concentrations. This procedure separated the effects of two dependent variables, Mg2+ and ATP4-/3- (ATPfree), to provide the following observations. (1) ATPfree, not Mg2+ (nor Ca2+), was the modifier. (2) ATPfree was an activator at low ionic strength and an inhibitor at high ionic strength, with half-maximal activation/inhibition occurring between 0.75 and 0.8 mM-ATPfree. (3) The rate constants controlling Vmax. with respect to actin were increased up to 3-fold by ATPfree at low ionic strength, and decreased up to 3-fold by ATPfree at high ionic strength. (4) The effect of ATPfree required near-native levels of the LC2 light chain bound to myosin (i.e. 2 mol of LC2/mol of myosin). (5) Sensitivity of P(i) liberation to a 50% decrease in the LC2 content of myosin required high ATPfree concentrations. It is concluded that LC2 and ATPfree are interdependent, non-additive, modifiers of MgATPase. These results are consistent with thin filament regulation of skeletal muscle contraction, and begin to explain why both positive and negative effects on MgATPase have been attributed to LC2.

scholarly journals The Study of Viability of Vibrio cholerae Strains in Low Ionic Strength Aquatic Environment

2019 ◽  
Author(s):  
Subha Sankar Paul ◽  
Eizo Takahashi ◽  
Goutam Chowdhury ◽  
Shin-ichi Miyoshi ◽  
Asish K. Mukhopadhyay ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Vibrio Cholerae ◽  
Aquatic Environment ◽  
Detection Rate ◽  
Environmental Water ◽  
Toxin Gene ◽  
Aquatic Medium ◽  
Vibrio Cholerae O1 ◽  
The Difference ◽  
Low Ionic Strength

It has been regarded that Vibrio cholerae O1 inhabit in environmental water. As many cholera patients emerge in Kolkata, it has been thought that V. cholerae O1 is easily detected in environmental water in Kolkata. However, the detection of V. cholerae O1 is rare, though other V. cholerae (NAG Vibrio) is constantly detected. To clear the reason for the difference of the detection rate of two Vibrios, we examined the viability of V. cholera O1 and NAG Vibrios in low ionic strength aquatic medium. We observed greater declining viability of V. cholerae O1 possessing cholera toxin gene (ctx) in low ionic strength solution, but the decline of NAG Vibrios non-possessing ctx is small. To evaluate the concerning of ctx in the viability, we examined the viabilities of V. cholerae O1which do not possess ctx and NAG Vibrios possessing ctx under the same condition. The result indicated that the existence of the ctx induces the decrease the viability of the host in low ionic strength solution. The decrease observed in this experiment might relate with the low detection of V. cholerae O1 possessing ctx in environmental water, though NAG Vibrio is constantly detected.

scholarly journals The interaction between β-lactoglobulin and sodium N-dodecyl sulphate

1976 ◽  
Vol 153 (3) ◽  
pp. 713-718 ◽  
Author(s):  
M N Jones ◽  
A Wilkinson
Keyword(s):  
Ionic Strength ◽  
Equilibrium Dialysis ◽  
Protein Molecule ◽  
Enthalpies Of Formation ◽  
Enthalpy Of Interaction ◽  
Surfactant Anion ◽  
Ionic Nature ◽  
Ph Range ◽  
Low Ionic Strength ◽  
Β Lactoglobulin

1. The binding of sodium n-dodecyl sulphate to β-lactoglobulin was studied in the pH range 3.5-7.0 by equilibrium dialysis, ultracentrifugation and microcalorimetry. 2. At low binding concentrations (less than 30 bound surfactants anions per protein molecule) the complexes formed aggregates in solution. 3. At higher binding concentrations aggregation does not occur at low ionic strength (0.01 mol/litre), but continues at high ionic strength (0.1 mol/litre). 4. At 25 degrees C the enthalpy of interaction of sodium n-dodecyl sulphate with β-lactoglobulin can be interpreted as the sum of the enthalpies of formation of a complex with 2 bound surfactant anions, with an enthalpy change of -9.5 kJ-mol-1 of bound surfactant, and complexes containing at least 22 bound surfactant anions, with limiting enthalpies per bound surfactant anion of -12.4 kJ-mol-1 at pH 3.5 and -3.25 kJ-mol-1 at pH 5.5. 5. The binding of surfactant and the enthalpy of interaction at pH 3.5 ARE NOT SIGNIFICANTLY AFFECTED BY THE ADDITION Of 8 M-urea. 6. The data indicate that at low binding concentrations the interaction is of an ionic nature, and is accompanied by a conformational change in the protein.

scholarly journals Native Ion Mobility Mass Spectrometry: when Gas Phase Ion Structures Depend on the Electrospray Charging Process

2018 ◽  
Author(s):  
Nina A. Khristenko ◽  
Jussara Amato ◽  
Sandrine Livet ◽  
Bruno Pagano ◽  
Antonio Randazzo ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Gas Phase ◽  
Ion Mobility ◽  
Droplet Surface ◽  
Dependent Manner ◽  
Base Pairs ◽  
Wide Range ◽  
A Chain ◽  
Gas Phase Ion ◽  
Low Ionic Strength

Ion mobility spectrometry (IMS) has become popular to characterize biomolecule folding. Numerous studies have shown that proteins that are folded in solution remain folded in the gas phase, whereas proteins that are unfolded in solution adopt more extended conformations in the gas phase. Here, we discuss how general this tenet is. We studied single-stranded DNAs (human telomeric cytosine-rich sequences with CCCTAA repeats), which fold into an intercalated motif (i-motif) structure in a pH-dependent manner, thanks to the formation of C‒H+‒C base pairs. As i-motif formation is favored at low ionic strength, we could investigate the ESI-IMS-MS behavior of i-motif structures at pH ~5.5 over a wide range of ammonium acetate concentrations (15 mM to 100 mM). The control experiments consisted of either the same sequence at pH ~7.5, wherein the sequence is unfolded, or sequence variants that cannot form i-motifs (CTCTAA repeats). The surprising results came from the control experiments. We found that the ionic strength of the solution had a greater effect on the compactness of the gas-phase structures than the solution folding state. This means that electrosprayed ions keep a memory of the charging process, which is influenced by the electrolyte concentration. We discuss these results in light of the analyte partitioning between the droplet interior and droplet surface, which in turn influences the probability of being ionized via a charged residue pathway or a chain extrusion pathway.<br>

scholarly journals Native Ion Mobility Mass Spectrometry: when Gas Phase Ion Structures Depend on the Electrospray Charging Process

2019 ◽  
Author(s):  
Nina A. Khristenko ◽  
Jussara Amato ◽  
Sandrine Livet ◽  
Bruno Pagano ◽  
Antonio Randazzo ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Gas Phase ◽  
Ion Mobility ◽  
Droplet Surface ◽  
Dependent Manner ◽  
Base Pairs ◽  
Wide Range ◽  
A Chain ◽  
Gas Phase Ion ◽  
Low Ionic Strength

Ion mobility spectrometry (IMS) has become popular to characterize biomolecule folding. Numerous studies have shown that proteins that are folded in solution remain folded in the gas phase, whereas proteins that are unfolded in solution adopt more extended conformations in the gas phase. Here, we discuss how general this tenet is. We studied single-stranded DNAs (human telomeric cytosine-rich sequences with CCCTAA repeats), which fold into an intercalated motif (i-motif) structure in a pH-dependent manner, thanks to the formation of C‒H+‒C base pairs. As i-motif formation is favored at low ionic strength, we could investigate the ESI-IMS-MS behavior of i-motif structures at pH ~5.5 over a wide range of ammonium acetate concentrations (15 mM to 100 mM). The control experiments consisted of either the same sequence at pH ~7.5, wherein the sequence is unfolded, or sequence variants that cannot form i-motifs (CTCTAA repeats). The surprising results came from the control experiments. We found that the ionic strength of the solution had a greater effect on the compactness of the gas-phase structures than the solution folding state. This means that electrosprayed ions keep a memory of the charging process, which is influenced by the electrolyte concentration. We discuss these results in light of the analyte partitioning between the droplet interior and droplet surface, which in turn influences the probability of being ionized via a charged residue pathway or a chain extrusion pathway.<br>

scholarly journals Binding of a tetracationic meso-porphyrin to polyadenylic acid: a spectroscopic study

2019 ◽  
Author(s):  
Olga Ryazanova ◽  
Igor Voloshin ◽  
Victor Zozulya
Keyword(s):  
Ionic Strength ◽  
Spectroscopic Study ◽  
The Self ◽  
Binding Modes ◽  
Polarized Fluorescence ◽  
Polyadenylic Acid ◽  
Wide Range ◽  
Emission Quenching ◽  
Low Ionic Strength ◽  
Fluorimetric Titration

Binding of a tetracationic porphyrin (TMPyP4+) to poly(rA) has been studied in neutral buffered solution of low ionic strength in a wide range of molar phosphate-to-dye ratios (P/D) using absorption spectroscopy, polarized fluorescence and fluorimetric titration. Two competitive binding modes were identified: partial intercalation of porphyrin chromophores between adenine bases prevailing at P/D > 20 and its outside binding to poly(rA) backbone dominating at P/D < 6. Both of them were accompanied by enhancement of the porphyrin emission. Absence of the emission quenching near stoichiometric P/D ratios allowed us to assume that external binding occurs without the self-stacking of the porphyrin chromophores.

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