Random Coil Behaviour of Proteins in Concentrated Urea Solutions

Measurements have been made of the intrinsic viscosities and osmotic pressures of protein polypeptide chains in concentrated urea solutions, in the presence of- ~-mercaptoethanol. The results show that both properties depend on molecular weight exactly as predicted for randomly coiled linear polymer chains. It can therefore be assumed that protein polypeptide chains, in the solvent medium employed, are random coils, r etaining practically no elements of their native conformation. In addition, from the osmotic pressure data, second virial coefficients have been calculated. By combining the intr insic . viscosities and second viri.al coefficients the unperturbed dimensions of protein polypeptide chains have been obtained. Their values , are in good agreement with those determined from the viscosity data alone

Random Coil Behaviour of Proteins in Concentrated Urea Solutions

Measurements have been made of the intrinsic viscosities and osmotic pressures of protein polypeptide chains in concentrated urea solutions, in the presence of- ~-mercaptoethanol. The results show that both properties depend on molecular weight exactly as predicted for randomly coiled linear polymer chains. It can therefore be assumed that protein polypeptide chains, in the solvent medium employed, are random coils, r etaining practically no elements of their native conformation. In addition, from the osmotic pressure data, second virial coefficients have been calculated. By combining the intr insic . viscosities and second viri.al coefficients the unperturbed dimensions of protein polypeptide chains have been obtained. Their values , are in good agreement with those determined from the viscosity data alone

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

Interactions of a-Chymotrypsinogen A with Some Alkylureas

The interactions of a-chymotrypsinogen A with urea, methyl-, N,N\u27-dimethyl-, ethyl-, N,N\u27-diethyl-, and propylurea were studied by means of calorimetry and circular dichroism. It has been found that the enthalpies of interaction of the alkylureas, with the exception of methylurea, with a-chymotrypsinogen A are distinctly from those of urea. Thus the transfer of the protein from water to aqueous urea and methylurea solutions is accompanied by release of heat, · i.e., the overall reaction is exothermic, whereas the transfer of the same protein to solutions of other alkylureas is characterized by consumption of heat, i.e., the overall reaction is endothermic. By examining the far UV CD spectra it can also be concluded that the alkylureas are clearly less efficient denaturants than urea. The difference in behavior reflects the presence of the hydrophobic moiety in the urea molecule

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

The Activity Coefficients of Amino Acids and Peptides in Aqueous Solutions Containing Guanidinium Chloride

Six systems of the type amino acid- or peptide-guanidinium chloride-water have been investigated over wide solute molality ranges using vapor pressure osmometry. The amino acids used were glycine and L-leucine, while the peptides were diglycine, triglycine, glycyl-L-leucine and L-leucyl-L-leucine. Equations for the ratios of the activity coefficients of these compounds in the salt solutions and water, respectively, were obtained in terms of the molalities of the solutes. The activity coefficient ratios for glycine are not much below one, whereas those for i.-leucine are considerably smaller reflecting the presence of the leucyl side chain. The activity coefficient ratios for the peptides are generally smaller than those for the amino acids which can be attributed to . the presence of the peptide group

The Activity Coefficients of Amino Acids and Peptides in Aqueous Solutions Containing Guanidinium Chloride

Six systems of the type amino acid- or peptide-guanidinium chloride-water have been investigated over wide solute molality ranges using vapor pressure osmometry. The amino acids used were glycine and L-leucine, while the peptides were diglycine, triglycine, glycyl-L-leucine and L-leucyl-L-leucine. Equations for the ratios of the activity coefficients of these compounds in the salt solutions and water, respectively, were obtained in terms of the molalities of the solutes. The activity coefficient ratios for glycine are not much below one, whereas those for i.-leucine are considerably smaller reflecting the presence of the leucyl side chain. The activity coefficient ratios for the peptides are generally smaller than those for the amino acids which can be attributed to . the presence of the peptide group

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

Interactions of a-Chymotrypsinogen A with Some Alkylureas

The interactions of a-chymotrypsinogen A with urea, methyl-, N,N\u27-dimethyl-, ethyl-, N,N\u27-diethyl-, and propylurea were studied by means of calorimetry and circular dichroism. It has been found that the enthalpies of interaction of the alkylureas, with the exception of methylurea, with a-chymotrypsinogen A are distinctly from those of urea. Thus the transfer of the protein from water to aqueous urea and methylurea solutions is accompanied by release of heat, · i.e., the overall reaction is exothermic, whereas the transfer of the same protein to solutions of other alkylureas is characterized by consumption of heat, i.e., the overall reaction is endothermic. By examining the far UV CD spectra it can also be concluded that the alkylureas are clearly less efficient denaturants than urea. The difference in behavior reflects the presence of the hydrophobic moiety in the urea molecule

Directed transport as a mechanism for protein folding in vivo

We propose a model for protein folding in vivo based on a Brownian-ratchet mechanism in the multidimensional energy landscape space. The device is able to produce directed transport taking advantage of the assumed intrinsic asymmetric properties of the proteins and employing the consumption of energy provided by an external source. Through such a directed transport phenomenon, the polypeptide finds the native state starting from any initial state in the energy landscape with great efficacy and robustness, even in the presence of different type of obstacles. This model solves Levinthal's paradox without requiring biased transition probabilities but at the expense of opening the system to an external field.Comment: 16 pages, 7 figure