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Abstract  

A simple method for determination of binding isotherm in the protein-ligand interaction was introduced using isothermal titration calorimetric data. This general method was applied to the study of the interaction of myelin basic protein (MBP) from bovine central nervous system with divalent copper ion at 27C in Tris buffer solution at pH=7.2. The binding isotherm for copper-MBP interaction is easily obtained by carrying out titration calorimetric experiment in two different concentrations of MBP. MBP has two binding sites for copper ion, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 0.083 and 1.740 ?M-1 in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement 21 of the binding affinity of the second site. The molar enthalpies of binding are -13.5 and -14.8 kJ mol-1 in the first and second binding sites, respectively.

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Abstract  

Heat divided by ligand concentration vs. heat, similar to the Scatchard plot, was introduced to obtain the equilibrium constant (K) and the enthalpy of binding (DH) using isothermal titration calorimetry data. Values of K and DH obtained by this linear pseudo-Scatchard plot for a system with a set of independent binding sites (such as binding fluoride ions on urease and monosaccharide methyl a-D-mannopyranoside on concavalin A) were remarkably like that obtained from a normal fitting Wiseman method and other our technical methods. On applying this graphical method to study the binding of copper ion on myelin basic protein (MBP), a concave downward curve obtained was consistent with the positive cooperativity in the binding. A graphical fitting by simple method for determination of thermodynamic parameters was also introduced. This method is general, without any assumption and restriction made in previous method. This general method was applied to the product inhibition study of adenosine deaminase.

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A thermodynamic study on the binding of magnesium with human growth hormone

Consideration of the new extended coordination model solvation parameters

Journal of Thermal Analysis and Calorimetry
Authors:
G. Rezaei Behbehani
and
A. Saboury

Abstract  

The thermodynamic parameters underlying the binding of Mg2+ to the hydrophobic core of human growth hormone, hGH, are determined using isothermal titration calorimetry. The interaction between Mg2+ and hGH (35 μM) was studied at 27°C in NaCl solution. A new solvation model was used to reproduce the enthalpies of Mg2+-hGH interaction over the whole Mg2+ concentrations. The solvation parameters recovered from the new salvation model, were correlated to the structural changes of hGH due to the metal ion interaction.

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Abstract  

A thermodynamic study on the interaction of bovine carbonic anhydrase II (CAII) with nickel ions was performed by using isothermal titration calorimetry (ITC) at 27 °C in Tris buffer solution at pH = 7.5. The enthalpies of Ni2+ + CAII interaction are reported and analysed in terms of the new solvation theory. It was indicated that there are three identical and non-cooperative sites for Ni2+. The binding of a nickle ion is exothermic with dissociation equilibrium constants of 81.306 and 99.126 μM at 27°C and 37°C, respectively. The binding of nickel ions can cause some changes in the stability of the enzyme at low and high Ni2+ concentrations.

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Abstract  

A simple graphical linear method was introduced for isothermal titration calorimetric data analysis in the protein-ligand interaction. The number of binding sites, the dissociation binding constant and the molar enthalpy of binding site can be obtained by using this new isothermal titration calorimetric data analysis method. The method was applied to the study of the interaction of human growth hormone (hGH) with divalent calcium ion at 27C in NaCl solution, 50 mM. hGH has a set of three identical and independent binding sites for Ca 2+ . The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 52 μMand -17.4, respectively. Results obtained by this new calorimetric data analysis are in good agreement with results obtained using our previous method.

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Abstract  

Binding properties of myelin basic protein (MBP) from bovine central nervous system due to the interaction by divalent magnesium ion (Mg2+) was investigated at 27°C in aqueous solution using isothermal titration calorimetry (ITC) technique. An extended solvation model was used to reproduce the enthalpies of Mg2+-MBP interaction over the whole Mg2+ concentrations. It was found that there is a set of two identical and noninteracting binding sites for Mg2+ ions. The dissociation equilibrium constant is K d=45.5 μM. The molar enthalpy of binding site is identical for both sites; ΔH=−15.24 kJ mol−1. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction.

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Abstract  

Thermodynamics of the interaction between erbium(III) chloride, Er3+, with human serum albumin (HSA), was investigated at pH 7.0 and in phosphate buffer by isothermal titration calorimetry. Our recently, solvation model was used to reproduce the enthalpies of HSA interaction by Er3+ over a broad range of metal ion concentration. The solvation parameters recovered from our new model, attributed to the structural change of HSA and its biological activity. The binding parameters for the interaction of Er3+ and HSA indicate that the concentrations of Er3+ have no significant effects on the structure of HSA.

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Abstract

A Thermodynamic study on the interaction Jack bean urease, JBU, with Cu2+ ion was studied by isothermal titration calorimetry (ITC) at 300 and 310 K in 30 mM Tris buffer solution, pH 7.0. The heats of JBU + Cu2+ interactions are reported and analyzed in terms of the extended solvation theory. It was indicated that there are a set of 12 identical and non-cooperative sites for Cu2+ ion. The binding of Cu2+ ion with JBU is exothermic with dissociation equilibrium constants of 284.883 and 345.855 μM at 300 and 310 K, respectively.

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Abstract

In this article, a thermodynamic study on the interaction of Jack bean urease, JBU, with and ions were studied by isothermal titration calorimetry (ITC) at 300 and 310 K in 30 mM Tris buffer solution, pH 7.0. The heats of and interactions are reported and analyzed in terms of the extended solvation model. It was indicated that there are a set of 12 identical and non-cooperative sites for and ions. The binding of and ions with JBU are exothermic with association equilibrium constants of 5415.65 and 4368.15 for and 2389 and 2087 for at 300 and 310 K, respectively.

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Abstract  

Binding properties and structural changes of human growth hormone (hGH) due to the interaction by cobalt ion (Co2+) were done at 27°C in NaCl solution, 50 mM, using different techniques of UV-Vis spectroscopy, circular dichroism (CD), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) techniques. There is a set of three identical and non-interacting binding sites for cobalt ions. The intrinsic association equilibrium constant and the molar enthalpy of binding obtained by ITC are 0.80 mM−1 and −16.70 kJ mol−1, respectively. The intrinsic association equilibrium constant obtained by a standard isothermal titration UV-Vis spectrophotometry method is also 0.79 mM−1, which is in good agreement with the value obtained from ITC. The Gibbs free energy and entropy changes due to the binding of cobalt ion on hGH are −16.67 kJ mol−1 and −0.1 J K−1 mol−1, respectively. Energetic domains analysis by DSC shows that phase transition of hGH in the presence of cobalt occurs at one main transition. Deconvolution of the main transition provides two sub-transitions with different values of the melting point and enthalpy of unfolding (33°C and 164 kJ mol−1 for the first and 49°C and 177 kJ mol−1 for the second, respectively). Interaction of cobalt ions with hGH prevents aggregation by an affect on the hydrophobicity of the protein macromolecule and provide useful information about its structure due to becoming reversible of protein thermal denaturation.

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