RESUMO
Self-assembling and dynamical properties of deoxyguanosine 5'-monophosphate in isotropic aqueous solutions were studied by (31)P NMR spectroscopy and dynamic light scattering (DLS). All solutions had the same c = 4 wt% guanosine concentration, while the added KCl molarity ranged from 0 to 1.5 M. (31)P NMR measurements show that potassium ions strongly enhance the stacking process of guanosine tetramers until a saturation is reached at 0.1 M KCl with more than 70% of the molecules aggregated. Polarized light scattering reveals the presence of a fast relaxation mode that arises from the translational dynamics of the self-assembled stacks. The diffusion coefficient of this mode shows a strong dependence on molarity of added salt, which can be described in terms of the coupled mode and counterion condensation theories for polyelectrolyte solutions. Depolarized light scattering reveals the rotational dynamics of the self-assembled stacks which exhibits a pronounced slowing down with increasing the added salt content.
Assuntos
Nucleotídeos de Desoxiguanina/química , Espectroscopia de Ressonância Magnética/métodos , Sais/farmacologia , Fenômenos Biofísicos , Biofísica , Análise de Fourier , Íons , Luz , Modelos Químicos , Modelos Teóricos , Isótopos de Fósforo/química , Potássio/química , Espalhamento de Radiação , Fatores de TempoRESUMO
A thermodynamic study of the isothermal interaction of human immunoglobulin G with guanidinium chloride, a strong denaturant, has been performed. Free energies of interaction were calculated using preferential binding data obtained by measuring densities at constant chemical potential and constant composition, respectively. Enthalpies of interaction were determined calorimetrically. The values of both thermodynamic parameters as well as those of entropies of interaction have been found to depend crucially on the extent of denaturant binding.
Assuntos
Guanidinas , Imunoglobulina G , Humanos , Matemática , TermodinâmicaRESUMO
A thermodynamic study of the isothermal interaction of beta-lactoglobulin with guanidinium chloride and urea has been performed. Enthalpies of interaction of the two denaturants have been obtained by calorimetric measurements, and the free energy of interaction calculated from previously determined preferential binding of denaturants. In separate dilatometric experiments the volume changes accompanying the interaction of guanidinium chloride with beta-lactoglobulin have also been determined.
Assuntos
Guanidinas , Lactoglobulinas , Ureia , Sítios de Ligação , Matemática , Ligação Proteica , Conformação Proteica , TermodinâmicaRESUMO
The osmotic coefficients, heats of dilution, and volume changes on dilution of aqueous solutions containing mixtures of polystyrenesulfonic acid and its lanthanum salt have been determined at 25 degrees C. The curve representing the osmotic coefficient as a function of the equivalent fraction of the acid has a maximum; the corresponding curves for the enthalpy and volume changes on dilution have a sigmoidal shape. Experimental results have been compared with predictions of the theory based on the cell model with cylindrical symmetry. A semiquantitative agreement between theory and experiment has been found.
Assuntos
Eletrólitos , Soluções , Lantânio , Matemática , Poliestirenos , Sais , Ácidos Sulfônicos , TermodinâmicaRESUMO
Dilatometry has become a useful method for the study of proteins owing to its simplicity and accuracy. However, it has seldom been used in the study of immunoglobulins. Therefore possible applications of the method for that study are being discussed. A description is also given of the most common experimental set-up and procedure for dilatometric experiments. Finally, several papers describing the application of dilatometry to the study of immunoglobulins are reviewed.
Assuntos
Físico-Química/instrumentação , Imunoglobulinas/análise , Técnicas Imunológicas , Reações Antígeno-Anticorpo , Guanidinas/farmacologia , Imunoglobulina G/metabolismo , Ligação ProteicaAssuntos
Guanidinas , Imunoglobulina G , Sítios de Ligação , Fenômenos Químicos , Físico-Química , Cromatografia DEAE-Celulose , Cromatografia em Gel , Diálise , Dissulfetos/análise , Ditioeritritol , Glutationa , Humanos , Fragmentos de Imunoglobulinas , Imunoglobulina G/isolamento & purificação , Matemática , Peso Molecular , Proteínas do Mieloma/isolamento & purificação , Oxirredução , Ligação Proteica , Conformação Proteica , Desnaturação Proteica , Solubilidade , Espectrofotometria Ultravioleta , UltracentrifugaçãoRESUMO
The heats of dilution of polyacrylic acid at four constant degrees of ionization (α = 0, 0.25, 0.50, and 1.00) have been measured in the concentration range 0.6-0.002 monomolal. The heat of dilution for pure acid (α = 0) is positive in the investigated concentration range, whereas it is negative for partially neutralized acid (α = 0.25 and 0.50). For completely neutralized add, for sodium polyacrylate (α = 1), the measured heat effects are exothermic at concentrations above about 0.05 monomolal. while below 0.05 M they become endothermic. The experimental results have been evaluated with the help of a previously developed theoretical treatment based on the cell model.
