Enthalpy of Denaturation of Chymotrypsinogen A in Aqueous Urea Solutions

Urea has been known as a strong denaturant for globular proteins. Numerous papers have been published in which the denaturing action of urea is described and attempts have been made to explain this action. Appropriate models have also been developed in order to calculate or at least estimate the difference in free enthalpy (i: G) between the native and denatured forms of protein molecules in urea solutions. For a number of proteins, e.g., B-lactoglobulin, L G\u27s for urea denaturation at different temperatures have been obtained by optical methods, e. g. difference spectroscopy or optical rotatory dispersion, and from them van\u27t Hoff\u27s enthalpy. For a detailed survey, the reader is referred to the review article of Tanford

The Partial Specific Volume of P-Lactoglobulin A in Aqueous Urea Solutions

The partial specific volume of ~-lactoglobulin A in 0.02 M NaCl - 0.01 M HCl containing different amounts of urea has been determined from density measurements. The partial specific volume first increases with urea concentration, reaches a maximum, decreases, reaches a minimum, and then increases again. In the interpretation of this behavior, the binding of urea to the protein and the imperfect atomic packing in native protein molecules have been assumed to be the dominant factors. From dilatometric experiments the differences between the partial molar volume of the protein in 0.02 M NaCl-0.01 M HCl with and without urea have been obtained. The values of the differences agree satisfactorily with those calculated from the partial specific volume. Furthermore, the volumes as well as their changes reflect the interaction of urea with the protein. Dilatometric experiments were also performed with the protein in 0.02 M NaCl to which urea was added. Comparison of the obtained results with those in 0.02 M NaCl-0.01 M HCl displays the fact that the partial specific volume is pH-dependent

Enthalpy of Denaturation of Chymotrypsinogen A in Aqueous Urea Solutions

Urea has been known as a strong denaturant for globular proteins. Numerous papers have been published in which the denaturing action of urea is described and attempts have been made to explain this action. Appropriate models have also been developed in order to calculate or at least estimate the difference in free enthalpy (i: G) between the native and denatured forms of protein molecules in urea solutions. For a number of proteins, e.g., B-lactoglobulin, L G\u27s for urea denaturation at different temperatures have been obtained by optical methods, e. g. difference spectroscopy or optical rotatory dispersion, and from them van\u27t Hoff\u27s enthalpy. For a detailed survey, the reader is referred to the review article of Tanford

Dynamic light scattering and

Self-assembling and dynamical properties of deoxyguanosine 5’-monophosphate in isotropic aqueous solutions were studied by 31P 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. 31P 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

Dynamic light scattering and \chem{^{31}P} NMR spectroscopy study of the self-assembly of deoxyguanosine \mth{5'}-monophosphate

Self-assembling properties of deoxyguanosine $5'$-monophosphate in isotropic solutions of concentrations from 0.5 wt% to 15 wt% were investigated by dynamic light scattering (DLS) and \chem{^{31}P} NMR spectroscopy. A slow diffusive mode with a diffusion coefficient $D_{\rm slow} \sim 10^{-12}$ m$^{2}$/s was detected by DLS for the whole concentration range. This mode is assigned to the translational motion of large globular aggregates, similar to those observed in DNA and other polyelectrolyte solutions. The existence of such aggregates was confirmed by freeze fracture electron microscopy. Close to the isotropic-cholesteric phase transition, at 4 wt% $\leqslant c \leqslant 10$ wt%, also a faster diffusive mode is observed in the polarized DLS response and a very fast mode is detected by depolarized DLS. These modes are related to translational and rotational diffusion of the columnar stacks of guanosine molecules, which are favorably formed in the relatively narrow pretransitional region. The stacking was also revealed from the appearance of a secondary resonance line in the \chem{^{31}P} NMR spectra. Using the hydrodynamic theory of Tirado and Garcia de la Torre, the length of the cylindrical stacks was found to be $L = 364 \pm 78$ Å, which is significantly larger than the values reported for other guanosine derivatives