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Biomedical subjects

S Lapanje

Publications and source records attributed to S Lapanje.

At least 19 recordsLinked to original sources
PubMed1996

Interactions of alpha-chymotrypsinogen A with alkylureas.

Solvation of alpha-chymotrypsinogen A (alpha-ctg A) in aqueous urea, methylurea, N,N'-dimethylurea and ethylurea was studied by density measurements. From the densities at constant molality and at constant chemical potential the preferential solvation parameters were determined. In urea and methylurea preferential solvation was observed, whereas in N,N'-dimethylurea and ethylurea at higher concentration water is preferentially bound. From preferential solvation data Gibbs free energy of transfer of alpha-ctg A from water to urea and alkylurea solutions were calculated. Since the enthalpies of transfer were determined previously, the entropies of transfer could also be obtained so that a complete thermodynamic description is available. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions involved in solvation as well as to calculate the exchange constant by using the model of weak interactions. In solvation of alkylureas the hydrophobic nature of the alkyl groups is clearly reflected.

Chemical Phenomena↗
PubMed1995

Thermodynamics of denaturation of alpha-chymotrypsinogen A in aqueous urea and alkylurea solutions.

The effects of pH, urea, and alkylureas on the thermal stability of alpha-chymotrypsinogen A (alpha-ctg A) have been investigated by differential scanning calorimetry (DSC) and UV spectroscopy. Heat capacity changes and enthalpies of transition of alpha-ctg A in the presence of urea and alkylureas were measured at the transition temperature. Using these data, the corresponding Gibbs free energies, enthalpies, and entropies of denaturation at 25 degrees C were calculated. Comparison of these values shows that at 25 degrees C denaturation with urea is characterized by a significantly smaller enthalpy and entropy of denaturation. At all denaturant concentrations the enthalpy term slightly dominates the entropy term in the Gibbs free energy function. The most obvious effect of alkylureas was lowering of the temperature of transition, which was increasing with alkylurea concentration and the size of alkyl chain. Destabilization of the folded protein in the presence of alkylureas appears to be primarily the result of the weakening of hydrophobic interactions due to diminished solvent ordering around the protein-molecules. At pH lower than 2.0, alpha-ctg A still exists in a very stable form, probably the acid-denatured from (A-form).

Calorimetry, Differential Scanning↗
PubMed1994

Denaturation behavior of alpha-chymotrypsinogen A in urea and alkylurea solutions: fluorescence studies.

The solvent denaturation of alpha-chymotrypsinogen (alpha-ctg A) in aqueous solution of urea, methyl-, N,N'-dimethyl-, ethyl-, propyl- and butylurea was studied by fluorescence measurements. Data were analyzed on the assumption of a two-state approximation to obtain the apparent equilibrium constant, Ku and the apparent Gibbs free energy of transition delta G0u. It has been observed that alkyl-substitution of urea significantly lowers the denaturant concentration needed to denature alpha-ctg A at 25 degrees C. Denaturation was accompanied by the red shift of emission maxima, the increase of the half-width of the fluorescence spectra, the increase of the fluorescence intensity, and the decrease of the fluorescence polarization. The differences of these fluorescence parameters observed for alpha-ctg A in alkylureas and urea can be ascribed to different unfolded states of the protein in different denaturant solutions. Minor differences in the extent of unfolding were confirmed by size-exclusion chromatography.

Animals↗
PubMed1993

Solvation of human serum albumin in aqueous alkylurea solutions.

Solvation of human serum albumin in aqueous solutions of urea, methyl-, N,N'-dimethyl-, and ethylurea was studied by density measurements. From the densities at constant molality and constant chemical potential, the preferential solvation parameters of human serum albumin were determined. In all solutions the denaturant is preferentially bound. From preferential solvation data, Gibbs free energies of transfer from water to alkylurea solutions were calculated. Since the enthalpies of transfer were determined previously the entropies of transfer would also be obtained. Based on these and model compound data an attempt is made to identify various interactions involved in solvation. The total binding of denaturant to protein could also be calculated from preferential solvation data. The following major binding sites have been identified: ionic groups on the surface of protein molecules, peptide groups and aromatic side-chains. The correlation between the total number of sites and the number of urea molecules bound is satisfactory.

Calorimetry↗
PubMed1992

Solvation of beta-lactoglobulin in alkylurea solutions.

Solvation of beta-lactoglobulin in aqueous solutions of urea, methyl-, N,N'-dimethyl- and ethylurea was studied by density measurements. From the densities at constant chemical potential and constant molality, the preferential solvation parameters and the partial specific volumes of beta-lactoglobulin in these solutions were determined. In urea and methylurea solutions urea is preferentially bound, whereas in N,N'-dimethyl- and ethylurea solutions at higher concentration water is preferentially bound. From preferential solvation data and partial specific volumes of protein Gibbs free energies of transfer from water to alkylurea solutions were calculated. Since the enthalpies of transfer were determined previously the entropies of transfer could also be obtained so that a complete thermodynamic description is available. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions involved in solvation. In salvation of alkylureas the hydrophobic nature of alkyl groups is clearly reflected.

Journal Article↗
PubMed1992

Apparent specific volumes of some dipeptides (containing L-valine and L-leucine in aqueous alkylurea solutions).

The apparent molal volumes of nine dipeptides containing glycine, L-valine, and L-leucine have been determined in methyl, N,N'-dimethyl and ethylurea solutions from precise density measurements. Limiting partial molal volumes. V2(0), at various solute concentrations have also been calculated. The experimental values of V2(0) in water agree reasonably well with those calculated as the sum of V2(0) of both acids after accounting for the electrostrictive effect and loss of water. There is no correlation between the values of V2(0) of individual dipeptides in alkylureas which means that the intrinsic volume and the electrostrictive effect make the largest contribution to V2(0). The contribution from other effects is within the limit of experimental error. The volumes of transfer from water to alkylurea solutions are all positive and reflect by and large the electrostrictive effect.

Amino Acid Sequence↗
PubMed1989

Calorimetric and circular dichroic studies of the thermal denaturation of beta-lactoglobulin.

The thermal denaturation of beta-lactoglobulin in aqueous solutions at pH 5.5 and 2.0 was investigated by differential scanning calorimetry (DSC) and circular dichroic (CD) measurements. By calorimetry, the denaturation temperatures (Td), denaturation enthalpies, and specific heat capacity changes for thermal denaturation in the temperature range scanned, i.e., 20-100 degrees C. The unfolding process was found to be only partially reversible. Analysis of the far-ultraviolet CD spectra reveals that with increasing temperature the mean residue ellipticity [( theta]) becomes less negative, which reflects unfolding of the native protein. At the highest temperature of CD measurements, i.e., 80 degrees C, conformational changes are to a large extent reversible.

Calorimetry, Differential Scanning↗
PubMed1988

Gibbs free energy of transfer of glycine and diglycine from water to alkylurea solutions. Measured vs. calculated values.

Ternary systems comprising water (1), glycine (diglycine) (2) and alkylurea (3) have been investigated using vapor pressure osmometry. Equations were obtained in terms of the molalities of the solutes for the activity coefficients of glycine and diglycine in these systems. The alkylureas used were methyl-, ethyl- and N, N'-dimethylurea. Using the activity coefficients the Gibbs free energy of transfer at infinite dilution of component 2 from water to alkylurea solutions was determined. Since the enthalpies of transfer are known, the corresponding entropies could also be obtained. Calculation of the Gibbs free energy of transfer at infinite dilution of component 2 rests on the assumption that it can be divided into two parts: the difference between the Gibbs free energy of cavity formation and that of interaction in the alkylurea solution and water, respectively. The first part was calculated by scaled particle theory using experimental density and surface tension data. The second part was taken to be due mainly to the change in dipole-dipole interactions.

Journal Article↗
PubMed1986

Interactions of myoglobin with urea and some alkylureas. II. Calorimetric and circular dichroic studies.

The interactions of myoglobin with urea, methyl-, N,N'-dimethyl- and ethylurea were studied by means of calorimetry and circular dichroism (CD). The enthalpies of transfer from water to aqueous denaturant solutions are positive for the alkylureas and negative for urea. The difference is due to the presence of hydrophobic groups in the alkylureas. Gibbs free energies of transfer for urea solutions were obtained from preferential binding data determined previously. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions between protein and denaturant. Analysis of the far-ultraviolet CD spectra reveals some differences in the denaturing activity of urea and the alkylureas, the latter being stronger denaturants than urea. Myoglobin displays relatively high stability towards these denaturants since concentrations above 5 M are needed for achieving major conformational changes.

Journal Article↗
PubMed1986

Interactions of myoglobin with urea and some alkylureas. I. Solvation in urea and alkylurea solutions.

The interactions of myoglobin with urea, methyl-, N,N'-dimethyl- and ethylurea in aqueous solutions were studied by density measurements. From the densities at constant chemical potential and constant molality, the partial specific volumes of myoglobin in these solutions as well as the extent of preferential binding of urea and alkylurea to myoglobin were determined. It has been found that water and not the denaturant is preferentially bound in urea solutions and alkylurea solutions up to 4 M so that the Gibbs free energy of myoglobin, i.e., its chemical potential in a denaturant solution, is larger than in water. This behavior of myoglobin is different from that of other globular proteins for which preferential binding of urea has been found. It appears that preferential hydration of myoglobin is due to its high content of ionic groups.

Animals↗
PubMed1981

Interactions of human serum albumin with some alkylureas.

The interactions of human albumin with urea, methyl-, N,N'-dimethyl-, ethyl-, N,N'-diethyl-, propyl-, and butylurea were studied by means of calorimetry and circular dichroism. It has been found that the enthalpies of interaction of the alkylureas with human serum albumin are distinctly different from those of urea. Thus, the transfer of the protein from water to aqueous urea solutions is accompanied by release of heat, i.e., the overall reaction is exothermic, whereas the transfer of the same protein of solutions of alkylureas is characterized by consumption of heat, i.e., the overall reaction is endothermic. By examining the far ultraviolet circular dichroism in behavior reflects the presence of the hydrophobic moiety in the urea molecule.

Calorimetry↗
PubMed1978

Thermodynamics of the isothermal interaction of human immunoglobulin G with guanidinium chloride.

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.

Guanidines↗
PubMed1978

Osmometric studies of human immunoglobulin G.

Osmometric studies of solutions of IgG and its H and L chains were performed in various solvents. It has been found that in aqueous solutions and in guanidinium chloride solutions of low and moderate concentrations IgG molecules are associated which prevents molecular weight determination. On the other hand, in 6 M guanidinium chloride the molecular weight of IgG was determined to be 145,000. Addition of sodium dodecyl sulfate to aqueous solutions of IgG does not prevent association.

Guanidines↗
PubMed1977

Thermodynamics of the isothermal interaction of beta-lactoglobulin with guanidinium chloride and urea.

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.

Binding Sites↗
PubMed1977

Studies on bovine spleen cathepsin D.

The purification procedure of cathepsin D which includes autolysis results in the destruction of the molecule to smaller polypeptide chains. Pure catepsin D obtained by the method which includes affinity chromatography, contains single polypeptide chain of 42000 daltons. The N-terminal amino acid is glycine. The specificity was studied using synthetic substrates. CD measurement of cathepsin D shows mainly unordered structure, about 26% of beta-structure and only 5% of alpha-helix. Binding of pepstatin shows pronounced changes in the CD spectrum between 250 and 300 nm; above 7.5 no interaction was observed.

Animals↗
PubMed1976

Thermodynamics of the isothermal denaturation of lysozyme by guanidinium chloride.

A thermodynamic analysis of the isothermal denaturation of lysozyme by guanidinium chloride has been performed. The analysis is based on the equation which relates the equilibrium constant for denaturation to the preferential binding of denaturant. The equation has been derived previously by thermodynamic methods, whereas in this article a derivation based on statistical mechanics is given. By application of the equation the free energy of denaturation is first calculated and from it, by subtracting the calorimetrically-determined enthalpy of denaturation, the entropy of denaturation is determined.

Binding Sites↗
PubMed1975

Dilatometry, a neglected method in immunological studies.

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.

Antigen-Antibody Reactions↗