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 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

Apparently Opposing Effects of Temperature and Guanidinium Chloride in the Denaturation of Ribonuclease A

The thermal denaturation of ribonuclease A in the presence of guanidinium chloride (GdmCl) was studied by means of circular dichroism (CD). In the presence of GdmCl the transition temperatures decrease with increasing denaturant concentration. However, closer examination of the results obtained shows the following feature: the negative values of molar ellipticity decrease with temperature in the absence of the denaturant; after the addition of the denaturant ellipticity minima appear at temperatures which depend on the denaturant concentration. The higher the GdmCl concentration the lower the temperature of the minimum. In 4 molar (and higher) GdmCl the minimum does not appear and the negative molar ellipticity increases throughout the whole temperature range examined. After reduction of the disulfide bonds, similar behaviour is observed with the minimum at each denaturant concentration being shifted towards a lower temperature. Though there is no obvious explanation for this behaviour, it appears that at the temperatures above the minimum some secondary structure is regained owing to decreased protein denaturant interactions

Medium-Dependent Antibacterial Properties and Bacterial Filtration Ability of Reduced Graphene Oxide

Toxicity of reduced graphene oxide (rGO) has been a topic of multiple studies and was shown to depend on a variety of characteristics of rGO and biological objects of interest. In this paper, we demonstrate that when studying the same dispersions of rGO and fluorescent Escherichia coli (E. coli) bacteria, the outcome of nanotoxicity experiments also depends on the type of culture medium. We show that rGO inhibits the growth of bacteria in a nutrition medium but shows little effect on the behavior of E. coli in a physiological saline solution. The observed effects of rGO on E. coli in different media could be at least partially rationalized through the adsorption of bacteria and nutrients on the dispersed rGO sheets, which is likely mediated via hydrogen bonding. We also found that the interaction between rGO and E. coli is medium-dependent, and in physiological saline solutions they form stable flocculate structures that were not observed in nutrition media. Furthermore, the aggregation of rGO and E. coli in saline media was observed regardless of whether the bacteria were alive or dead. Filtration of the aggregate suspensions led to nearly complete removal of bacteria from filtered liquids, which highlights the potential of rGO for the filtration and separation of biological contaminants, regardless of whether they include live or dead microorganisms