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

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

Pattern of Elemental Release During the Granite Dissolution Can Be Changed by Aerobic Heterotrophic Bacterial Strains Isolated from Damma Glacier (Central Alps) Deglaciated Granite Sand

Colonisation and weathering of freshly deglaciated granite are key processes in initial soil formation and development. We have obtained 438 isolates from granite sand covering glacial toe, 284 isolates at 22°C and 154 at 4°C incubation temperatures, respectively, to obtain cultures for the investigation of their weathering capabilities under laboratory conditions. The isolation of bacteria from granite sand was performed on rich-, intermediate- and low-nutrient-content solid media. Isolates were identified by 16S rRNA gene sequencing. According to the genera-associated weathering capabilities described in the literature and according to their abundance in our culture collection, we selected eight strains to analyse their effects on the weathering dynamics of granite sand during the batch culture experiment. Analysis of culturable bacteria showed higher species richness among isolates from 22°C than from 4°C incubations. In the R2A and 1/100 Ravan media, we observed the highest species richness of isolates obtained at 22°C and 4°C incubation temperatures, respectively. The obtained 16S rRNA sequences revealed the presence of alpha-, beta- and gamma-proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. The most numerous group of isolates was distantly related to Collimonas representatives, and according to the sequences of the 16S rRNA genes, they can form a new genus. Isolates from this group had the capability of causing increased dissolution rates for Fe, W, Ni and Rb. In general, at each sampling during the 30-day experiment, every strain showed a unique weathering profile resulting from differential rates of the dissolution and the precipitation of different minerals in the batch culture. Consequently, the presence of different strains, their growth stage and changes in proportions of strains in the bacterial community can affect further soil development and the successive colonisation by plant