SEARCH · Search PubMed

Results for “CALORIMETRY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,495 records · Page 83Linked to original sources

PubMed1998

Thermodynamics of the reconstitution of tuna cytochrome c from two peptide fragments.

Two peptide fragments from tuna cytochrome c (cyt c), N-fragment (residues 1-44 containing the heme) and C-fragment (residues 45-103), combine to form a 1:1 fragment complex. This was clearly proved by ion-spray mass spectrometry. It was found from CD and NMR spectra that the structure of the fragment complex formed is similar to that of an intact cyt c, although each isolated fragment itself is unstructured. Binding constants and enthalpies upon the complex formation were directly observed by isothermal titration calorimetry. Thermodynamic parameters (deltaG(o)b, deltaHb, deltaS(o)b, and deltaC(b)p)) associated with the complex formation were determined at various pHs and temperatures. DeltaHb was found to be almost independent of pH values. The change in heat capacity accompanying the complex formation (deltaC(b)p) was directly determined from the temperature dependence of deltaHb. In addition, the change in heat capacity and enthalpy upon tuna cyt c unfolding were determined by differential scanning calorimetry. Thermodynamic parameters for the unfolding/dissociation process of the fragment complex were compared with those for cyt c unfolding at pH 3.9 and 303 K. In a comparison of two unfolding processes, the heat capacity change of each was very close to the other, while both the unfolding enthalpy and entropy of the fragment complex were larger than those of tuna cyt c. These thermodynamic data suggest that the internal interactions between polar groups (hydrogen bonding) and nonpolar groups (van der Waals interactions) are preserved in the fragment complex as well as in the native state of cyt c.

Animals↗

PubMed1999

The energetics of HMG box interactions with DNA: thermodynamic description of the target DNA duplexes.

The thermal properties and energetics of formation of 10, 12 and 16 bp DNA duplexes, specifically interacting with the HMG box of Sox-5, have been studied by isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). DSC studies show that the partial heat capacity of these short duplexes increases considerably prior to the cooperative process of strand separation. Direct extrapolation of the pre and post-transition heat capacity functions into the cooperative transition zone suggests that unfolding/dissociation of strands results in no apparent heat capacity increment. In contrast, ITC measurements show that the negative enthalpy of complementary strand association increases in magnitude with temperature rise, implying that strand association proceeds with significant decrease of heat capacity. Furthermore, the ITC-measured enthalpy of strand association is significantly smaller in magnitude than the enthalpy of cooperative unfolding measured by DSC. To resolve this paradox, the heat effects upon heating and cooling of the separate DNA strands have been measured by DSC. This showed that cooling of the strands from 100 degrees C to -10 degrees C proceeds with significant heat release associated with the formation of intra and inter-molecular interactions. When the enthalpy of residual structure in the strands and the temperature dependence of the heat capacity of the duplexes and of their unfolded strands have been taken into account, the ITC and DSC results are brought into agreement. The analysis shows that the considerable increase in heat capacity of the duplexes with temperature rise is due to increasing fluctuations of their structure (e.g. end fraying and twisting) and this effect obscures the heat capacity increment resulting from the cooperative separation of strands, which in fact amounts to 200(+/-40) JK(-1) (mol bp)(-1). Using this heat capacity increment, the averaged standard enthalpy, entropy and Gibbs energy of formation of fully folded duplexes from fully unfolded strands have been determined at 25 degrees C as -33(+/-2) kJ (mol bp)(-1), -93(+/-4) J K(-1) (mol bp)(-1) and -5.0(+/-0.5) kJ (mol bp)(-1), respectively.

Animals↗

PubMed1999

The energetics of HMG box interactions with DNA: thermodynamics of the DNA binding of the HMG box from mouse sox-5.

The energetics of the Sox-5 HMG box interaction with DNA duplexes, containing the recognition sequence AACAAT, were studied by fluorescence spectroscopy, isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). Fluorescence titration showed that the association constant of this HMG box with the duplexes is of the order 4x10(7) M(-1), increasing somewhat with temperature rise, i.e. the Gibbs energy is -40 kJ mol(-1) at 5 degrees C, decreasing to -48 kJ mol(-1) at 32 degrees C. ITC measurements of the enthalpy of association over this temperature range showed an endothermic effect below 17 degrees C and an exothermic effect above, suggesting a heat capacity change on binding of about -4 kJ K(-1) mol(-1), a value twice larger than expected from structural considerations. A straightforward interpretation of ITC data in heat capacity terms assumes, however, that the heat capacities of all participants in the association reaction do not change over the considered temperature range. Our previous studies showed that over the temperature range of the ITC experiments the HMG box of Sox-5 starts to unfold, absorbing heat and the heat capacities of the DNA duplexes also increase significantly. These heat capacity effects differ from that of the DNA/Sox-5 complex. Correcting the ITC measured binding enthalpies for the heat capacity changes of the components and complex yielded the net enthalpies which exhibit a temperature dependence of about -2 kJ K(-1) mol(-1), in good agreement with that predicted on the basis of dehydration of the protein-DNA interface. Using the derived heat capacity change and the enthalpy and Gibbs energy of association measured at 5 degrees C, the net enthalpy and entropy of association of the fully folded HMG box with the target DNA duplexes was determined over a broad temperature range. These functions were compared with those for other known cases of sequence specific DNA/protein association. It appears that the enthalpy and entropy of association of minor groove binding proteins are more positive than for proteins binding in the major groove. The observed thermodynamic characteristics of protein binding to the A+T-rich minor groove of DNA might result from dehydration of both polar and non-polar groups at the interface and release of counterions. The expected entropy of dehydration was calculated and found to be too large to be compensated by the negative entropy of reduction of translational/rotational freedom. This implies that DNA/HMG box association proceeds with significant decrease of conformational entropy, i.e. reduction in conformational mobility.

Animals↗

PubMed2007

Systems-level adaptations explain chronic tolerance development to nitrous oxide hypothermia in young and mature rats.

RATIONALE: Nitrous oxide (N(2)O) can initially lower core temperature (T (core)), but hypothermic tolerance develops with chronic administration. Therefore, one or both of T (core)'s controlling determinants, heat production (HP) and heat loss (HL), must adapt across repeated N(2)O administrations. Simultaneous measurements of HP, HL, and T (core) during chronic N(2)O administrations will elucidate this adaptive process and constitute a rigorous model for studying the systems-level dynamics of tolerance in both mature and young animals. This approach is justified by the need to better understand the increased vulnerability to addiction associated with adolescent drug use. OBJECTIVES: The objective of the study was to measure HL and HP across repeated steady-state administrations of 60% N(2)O in young and mature rats. MATERIALS AND METHODS: Synchronous measurements of HP (indirect calorimetry), HL (direct calorimetry), and T (core) (telemetry) were obtained during 60% N(2)O administrations in adolescent (28-45 days, n = 11) and mature rats (>90 days, n = 8). Rats received five 90-min drug exposures (every other day). RESULTS: Compared to mature rats, adolescents initially exhibited greater hypothermia, but acquired tolerance more rapidly and actually developed hyperthermia during the fifth administration. In both groups, N(2)O consistently increased HL, but progressive increases of intrasessional HP over repeated administrations prevented hypothermia and subsequently promoted hyperthermia in adolescent rats. CONCLUSIONS: Adolescent rats hyper-adapt to N(2)O hypothermia. Increases of intrasessional HP across N(2)O administrations explained both tolerance to N(2)O hypothermia and the unexpected hyperthermia observed in adolescents. These findings raise the possibility that the increased vulnerability to addiction associated with adolescent drug use involves a hyper-adaptive tolerance mechanism.

Administration, Inhalation↗

PubMed1992

Thermodynamic analysis of heparin binding to human antithrombin.

The binding of heparin to human antithrombin III (ATIII) was investigated by titration calorimetry (TC) and differential scanning calorimetry (DSC). TC measurements of homogeneous high-affinity pentasaccharide and octasaccharide fragments of heparin in 0.02 M phosphate buffer and 0.15 M sodium chloride (pH 7.3) yielded binding constants of (7.1 +/- 1.3) x 10(5) M-1 and (6.7 +/- 1.2) x 10(6) M-1, respectively, and corresponding binding enthalpies of -48.3 +/- 0.7 and -54.4 +/- 5.4 kJ mol-1. The binding enthalpy of heparin in phosphate buffer (0.02 M, 0.15 M NaCl, pH 7.3) was estimated from TC measurements to be -55 +/- 10 kJ mol-1, while the enthalpy in Tris buffer (0.02 M, 0.15 M NaCl, pH 7.3) was -18 +/- 2 kJ mol-1. The heparin-binding affinity was shown by fluorescence measurements not to change under these conditions. The 3-fold lower binding enthalpy in Tris can be attributed to the transfer of a proton from the buffer to the heparin-ATIII complex. DSC measurements of the ATIII unfolding transition exhibited a sharp denaturation peak at 329 +/- 1 K with a van 't Hoff enthalpy of 951 +/- 89 kJ mol-1, based on a two-state transition model and a much broader transition from 333 to 366 K. The transition peak at 329 K accounted for 9-18% of the total ATIII. At sub-saturate heparin concentrations, the lower temperature peak became bimodal with the appearance of a second transition peak at 336 K. At saturate heparin concentration only the 336 K peak was observed. This supports a two domain model of ATIII folding in which the lower stability domain (329 K) binds and is stabilized by heparin.

Animals↗

PubMed2006

Temperature and pressure effects on structural and conformational properties of POPC/SM/cholesterol model raft mixtures--a FT-IR, SAXS, DSC, PPC and Laurdan fluorescence spectroscopy study.

We report on the effects of temperature and pressure on the structure, conformation and phase behavior of aqueous dispersions of the model lipid "raft" mixture palmitoyloleoylphosphatidylcholine (POPC)/bovine brain sphingomyelin (SM)/cholesterol (Chol) (1:1:1). We investigated interchain interactions, hydrogen bonding, conformational and structural properties as well as phase transformations of this system using Fourier transform-infrared (FT-IR) spectroscopy, small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) coupled with pressure perturbation calorimetry (PPC), and Laurdan fluorescence spectroscopy. The IR spectral parameters in combination with the scattering patterns from the SAXS measurements were used to detect structural and conformational transformations upon changes of pressure up to 7-9 kbar and temperature in the range from 1 to about 80 degrees C. The generalized polarization function (GP) values, obtained from the Laurdan fluorescence spectroscopy studies also reveal temperature and pressure dependent phase changes. DSC and PPC were used to detect thermodynamic properties accompanying the temperature-dependent phase changes. In combination with literature fluorescence spectroscopy and microscopy data, a tentative p,T stability diagram of the mixture has been established. The data reveal a broad liquid-order/solid-ordered (lo+so) two-phase coexistence region below 8+/-2 degrees C at ambient pressure. With increasing temperature, a lo+ld+so three-phase region is formed, which extends up to approximately 27 degrees C, where a liquid-ordered/liquid-disordered (lo+ld) immiscibility region is formed. Finally, above 48+/-2 degrees C, the POPC/SM/Chol (1:1:1) mixture becomes completely fluid-like (liquid-disordered, ld). With increasing pressure, all phase transition lines shift to higher temperatures. Notably, the lo+ld (+so) phase coexistence region, mimicking raft-like lateral phase separation in natural membranes, extends over a rather wide temperature range of about 40 degrees C, and a pressure range, which extends up to about 2 kbar for T=37 degrees C. Interestingly, in this pressure range, ceasing of membrane protein function in natural membrane environments has been observed for a variety of systems.

2-Naphthylamine↗

PubMed2004

Reversible unfolding of beta-sheets in membranes: a calorimetric study.

The hexapeptide acetyl-Trp-Leu(5) (AcWL(5)) has the remarkable ability to assemble reversibly and spontaneously into beta-sheets on lipid membranes as a result of monomer partitioning followed by cooperative assembly. This system provides a unique opportunity to study the thermodynamics of protein folding in membranes, which we have done using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). The results, which may represent the first example of reversible thermal unfolding of peptides in membranes, help to define the contribution of hydrogen bonding to the extreme thermal stability of membrane proteins. ITC revealed that the enthalpy change for partitioning of monomeric, unstructured AcWL(5) from water into membranes was zero within experimental error over the temperature range of 5 degrees C to 75 degrees C. DSC showed that the beta-sheet aggregates underwent a reversible, endothermic, and very asymmetric thermal transition with a concentration-dependent transition temperature (T(m)) in the range of 60 degrees C to 80 degrees C. A numerical model of nucleation and growth-dependent assembly of oligomeric beta-sheets, proposed earlier to describe beta-sheet formation in membranes, recreated remarkably well the unusual shape and concentration-dependence of the transition peaks. The enthalpy for thermal unfolding of AcWL(5) beta-sheets in the membrane was found to be about 8(+/-1)kcal mol(-1), or about 1.3(+/-0.2)kcal mol(-1) per residue.

Calorimetry↗

PubMed1999

Interaction mode specific reorganization of gel phase monoglyceride bilayers by beta-lactoglobulin.

The interaction between beta-lactoglobulin and sonicated aqueous dispersions of the gel phase forming monoglyceride monostearoylglycerol were studied using isothermal titration calorimetry, direct binding experiments, differential scanning calorimetry, leakage of a fluorescent dye and solid-state (31)P- and (2)H-NMR. In the absence of a charged amphiphile, monostearoylglycerol forms a precipitate. Under these conditions, no interaction with beta-lactoglobulin was observed. In the presence of the negatively charged amphiphile dicetylphosphate, the gel phase monostearoylglycerol formed stable and closed, probably unilamellar, vesicles with an average diameter of 465 nm. beta-Lactoglobulin interacts with these bilayer structures at pH 4, where the protein is positively charged, as well as at pH 7 where the protein is negatively charged. Under both conditions of pH, the binding affinity of beta-lactoglobulin is in the micromolar range as observed with ITC and the direct binding assay. At pH 4, two binding modes were found, one of which is determined with ITC while the direct binding assay determines the net result of both. The first binding mode is observed with ITC and is characterized by a large binding enthalpy, a decreased enthalpy of the MSG L(beta) to L(alpha) phase transition and leakage of a fluorescent dye. These characteristics are explained by a beta-lactoglobulin induced partial L(beta) to coagel phase transition that results from a specific electrostatic interaction between the protein and the charged amphiphile. This explanation is confirmed by solid-state (2)H-NMR using 1-monostearoylglycerol with a fully deuterated acyl chain. Upon interaction with beta-lactoglobulin, the isotropic signal in the (2)H-NMR spectrum of the monostearoylglycerol-dicetylphosphate mixture partially transforms into a broad anisotropic signal which could be assigned to coagel formation. The second binding mode probably results from an aspecific electrostatic attraction between the negatively charged bilayer and the positively charged protein and causes the precipitation of the dispersion. At pH 7, only the first binding mode is observed.

Animals↗

PubMed2001

Myo-inositol hexasulphate and low molecular weight heparin binding to human acidic fibroblast growth factor: a calorimetric and FTIR study.

The interaction of an amino-terminal-truncated 139 amino-acids form of human acidic fibroblast growth factor with myo-inositol hexasulphate and low molecular weight (3500 g mol(-1)) heparin has been studied by isothermal titration calorimetry, differential scanning calorimetry and Fourier transform infrared spectroscopy. A slightly higher affinity for the monosaccharide has been measured. The binding of the ligands causes an increase of 13--15 degrees C in the melting temperature of the free protein (45 degrees C). From measured enthalpy and heat capacity changes, calculations of changes in accessible surface areas have been made. These calculations, together with infrared spectroscopy data, indicate that a small conformational change is induced by the binding of both ligands. This conformational change would affect the tertiary structure, not the secondary one.

Calorimetry, Differential Scanning↗

PubMed1987

[Evaluation of the Engstrom metabolic computer].

The Engstrom Metabolic Computer (EMC), in association with the Erica Ventilator, uses indirect calorimetry to carry out continuous on-line gas exchange measurements. A laboratory assessment of the different parts of this equipment is described. The variability of FIO2 was less than 0.05. The accuracy and stability of the inspiratory flowmeter were only slightly modified by changes in the I/E ratio and gas flow rates. The overestimation of flow on increasing FIO2 was taken into account by the computer. The hygrometry of inspiratory and expiratory air samples reached that of room air, with an absence of saturation during prolonged measurements. The CO2 analyser also showed a good stability. The accuracy of the oxygen cell needed to be checked periodically. A global evaluation was carried out using Damask's method: a lung model was used into which CO2 and N2 were insufflated at precise rates to simulate CO2 production and O2 consumption. The measured respiratory quotient was also compared with the known RQ of burning methanol. The difference between measured and real values was less than 5%. Therefore, it was concluded that the EMC was reliable for indirect calorimetry measurements.

Calorimetry↗

PubMed1992

Enthalpic destabilization of a mutant human lysozyme lacking a disulfide bridge between cysteine-77 and cysteine-95.

To understand the role of disulfide bridges in protein stability, the thermodynamic changes in the denaturation of two mutant human lysozymes lacking a disulfide bridge between Cys-77 and Cys-95 (C77A and C77/95A) were analyzed using differential scanning calorimetry (DSC). At pH 3.0 and 57 degrees C, the stabilities of both the C77A and C77/95A mutants were decreased about 4.6 kcal.mol-1 in Gibbs free energy change. Under the same conditions, the enthalpy changes (delta H) were 94.8 and 90.8 kcal.mol-1, respectively, which were smaller than that of the wild type (100.8 kcal.mol-1). The destabilization of the mutants was caused by enthalpic factors. Although X-ray crystallography indicated that the mutants preserve the wild-type tertiary structure, removal of the disulfide bridge increased the flexibility of the native state of the mutants. This was indicated both by an increase in the crystallographic thermal factors (B-factors) and by a decrease in the affinity of N-acetylglucosamine trimer [(NAG)3] observed using isothermal titration calorimetry (DTC) due to entropic effects. Thus, the effect of cross-linking on the stability of a protein is not solely explained by the entropy change in denaturation.

Amino Acid Sequence↗

PubMed1989

Thermodynamics of intersubunit interactions in cholera toxin upon binding to the oligosaccharide portion of its cell surface receptor, ganglioside GM1.

The binding and the energetics of the interaction of cholera toxin with the oligosaccharide portion of ganglioside GM1 (oligo-GM1), the toxin cell surface receptor, have been studied by high-sensitivity isothermal titration calorimetry and differential scanning calorimetry. Previously, we have shown that the association of cholera toxin to ganglioside GM1 enhances the cooperative interactions between subunits in the B-subunit pentamer [Goins, B., & Freire, E. (1988) Biochemistry 27, 2046-2052]. New experiments presented in this paper reveal that the oligosaccharide portion of the receptor is by itself able to enhance the intersubunit cooperative interactions within the B pentamer. This effect is seen in the protein unfolding transition as a shift from independent unfolding of the B promoters toward a cooperative unfolding. To identify the origin of this effect, the binding of cholera toxin to oligo-GM1 has been measured calorimetrically under isothermal conditions. The binding curve at 37 degrees C is sigmoidal, indicating cooperative binding. The binding data can be described in terms of a nearest-neighbor cooperative interaction binding model. In terms of this model, the association of a oligo-GM1 molecule to a B protomer affects the association to adjacent B promoters within the pentameric ring. The measured intrinsic binding enthalpy per protomer is -22 kcal/mol and the cooperative interaction enthalpy -11 kcal/mol. The intrinsic binding constant determined calorimetrically is 1.05 x 10(6) M-1 at 37 degrees C and the cooperative Gibbs free energy equal to -850 cal/mol.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗

PubMed1998

Thermodynamics of bovine spleen galectin-1 binding to disaccharides: correlation with structure and its effect on oligomerization at the denaturation temperature.

Isothermal titration calorimetry (ITC) measurements of the binding 1-beta carbohydrate-substituted galactopyranoside derivatives to galectin-1 from bovine spleen, a dimer with one binding site per subunit, were performed at 283-285 and 298 K. The disaccharides were lactose, methyl beta-lactoside, lactulose, 4-O-beta-D-galactopyranosyl-D-mannopyranoside, 3-O-beta-D-galactopyranosyl-D-arabinose, 2'-O-methyllactose, lacto-N-biose, N-acetyllactosamine, and thiodigalactopyranoside. The site binding enthalpies, DeltaHb, are the same at both temperatures and range from -42.2 +/- 3.3 kJ mol-1 for thiodigalactopyranoside to -24.5 +/- 0.5 kJ mol-1 for lacto-N-biose, and the site binding constants range from 4.86 +/- 0.78 x 10(3) M-1 for methyl beta-lactoside at 297.8 K to 6.54 +/- 0.97 x 10(4) M-1 for N-acetyllactosamine at 281.3 K. The binding reactions are enthalpically driven, exhibit enthalpy-entropy compensation, and, with the exception of N-acetyllactosamine, follow a van't Hoff dependence of the binding constant on temperature. The number of contacts at distances <4.0 A between the disaccharide and galectin was determined from the energy-minimized conformation of the complex derived from the X-ray crystallographic structure of the galectin-N-acetyllactosamine complex determined by Liao et al. [Liao, D. I., Kapadia, G., Ahmed, H., Vasta, G. R., and Herzberg, O. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 1428-1432]. The binding enthalpies calculated from changes in the solvent-accessible surface areas of the galectin binding site upon binding of the disaccharide were in close agreement with the experimental values for lactose, lactulose, lacto-N-biose, and N-acetyllactosamine, all of which exhibit binding enthalpies >-36 kJ mol-1. Differential scanning calorimetry measurements on solutions of galectin and its disaccharide complexes show that the galectin dimer does not dissociate upon denaturation in contrast to the legume lectins. At the denaturation temperature, the galectin in the absence of sugar exists as a tetramer, and the extent of this association is substantially reduced in the presence of a disaccharide.

Animals↗

PubMed2000

Influence of monovalent cations on rat alpha- and beta-parvalbumin stabilities.

The mammalian genome encodes both alpha- and beta-parvalbumin isoforms. The rat beta-parvalbumin (aka "oncomodulin") is more stable than the alpha isoform at physiological pH and ionic strength, despite its substantially higher charge density and truncated C-terminal helix [Henzl, M. T., and Graham, J. S. (1999) FEBS Lett. 442, 241-245]. Reasoning that solvent interactions could contribute to this unexpected finding, we have examined the stabilities of the Ca(2+)-free alpha- and beta-parvalbumins as a function of Na(+) and K(+) concentration. Differential scanning calorimetry data suggest that, at physiological pH and ionic strength, the beta isoform binds roughly 2 equiv of Na(+) or a single equivalent of K(+) with moderate affinity. Under comparable conditions, the alpha isoform apparently binds just 1 equiv of Na(+) and essentially no K(+). Isothermal titration calorimetry experiments suggest that the bound monovalent ions occupy the EF-hand motifs. In 0.15 M K(+), at pH 7.4, the stability of the apo-beta-parvalbumin exceeds that of the alpha isoform by approximately 2.6 kcal/mol at 37 degrees C and by approximately 3.0 kcal/mol at 25 degrees C. The latter value represents a substantial fraction of the difference in Ca(2+)-binding free energies measured in vitro for the two proteins. Significantly, however, these results do not completely explain the paradoxical stability of the beta isoform, which maintains its higher melting temperature under all conditions examined.

Amino Acid Sequence↗

PubMed2006

Energetics in correlation with structural features: the case of micellization.

Understanding micellization processes at the molecular level has direct relevance for biological self-assembly, folding, and association processes. As such, it requires complete characterization of the micellization thermodynamics, including its correlation with the corresponding structural features. In this context, micellization of a series of model non-ionic surfactants (poly(ethylene glycol) monooctyl ethers, C(8)E(gamma)) was studied by isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). The corresponding structural properties of C(8)E(gamma) micelles were investigated by small-angle X-ray scattering (SAXS). The C(8)E(gamma) micellization, characterized independently from ITC, DSC, and structural data, reveals that deltaH(M)(o) > 0, deltaS(M)(o) > 0, and deltaC(P)(M)(o) < 0, while the dissection of its energetics shows that it is primarily governed by the transfer of 20-30 C(8) alkyl chains from aqueous solution into the nonpolar core (r approximately 1.3 nm) of the spherical micelle. Moreover, thermodynamic parameters of micellization, estimated from the structural features related to the changes in solvent-accessible surface areas upon micellization, are in a good agreement with the corresponding parameters obtained from the analysis of ITC and DSC data. We have shown that the contributions to deltaS(M)(o) other than from hydration (deltaS(M)(other)(o)), estimated from experimental data, appear to be small (deltaS(M)(other)(o) < 0.1 deltaS(M)(other)(o)) and agree well with the theoretical estimates expressed as a sum of the corresponding translational, conformational, and size contributions. These deltaS(M)(other)(o) contributions are much less unfavorable than those estimated for a rigid-body association, which indicates the dynamic nature of the C(8)E(gamma) micellar aggregates. the dynamic nature of the C8EY micellar aggregates.

Calorimetry↗

PubMed2006

Contributions of hydroxyethyl groups to the DNA binding affinities of anthracene probes.

Contributions of hydroxyethyl functions to the DNA binding affinities of substituted anthracenes are evaluated by calorimetry and spectroscopy. Isothermal titration calorimetry indicated that binding of the ligands to calf thymus DNA (5 mM Tris buffer, 50 mM NaCl, pH 7.2, 25 degrees C) is exothermic. The binding constants increased from 1.5 x 10(4) to 1.7 x 10(6) M(-1) as a function of increase in the number of hydroxyethyl functions (0-4). DNA binding was accompanied by red-shifted absorption (approximately 630 cm(-1)), strong hypochromism (>65%), positive induced-circular dichroism bands, and negative linear dichroism signals. DNA binding, in general, increased the helix stabilities to a significant extent (DeltaT(m) approximately 7 degrees C, DeltaDeltaH approximately 3 kcal/mol, DeltaDeltaS approximately 6-20 cal/K.mol). The binding constants showed a strong correlation with the number of hydroxyethyl groups present on the anthracene ring system. Analysis of the binding data using the hydrophobicity parameter (Log P) showed a poor correlation between the binding affinity and hydrophobicity. This observation was also supported by a comparison of the affinities of probes carrying N-ethyl (Kb = 0.8 x 10(5) M(-1)) versus N-hydroxyethyl side chains (Kb = 5.5 x 10(5) M(-1)). These are the very first examples of a strong quantitative correlation between the DNA binding affinity of a probe and the number of hydroxyethyl groups present on the probe. These quantitative findings are useful in the rational design of new ligands for high-affinity binding to DNA.

Anthracenes↗

PubMed2003

Three important calorimetric applications of a classic thermodynamic equation.

The thermodynamic background to three calorimetric techniques is discussed; (i) titration microcalorimetry, (ii) adiabatic calorimetry, and (iii) heat conduction calorimetry. Relevant equations for each technique are derived from a common equation for the enthalpy H of a closed system. General patterns which emerge in the measured parameters are presented for adiabatic and heat conduction calorimeters linked to applications of these techniques.

Calorimetry↗

PubMed2002

Binding of ATP to heat shock protein 90: evidence for an ATP-binding site in the C-terminal domain.

The presence of a nucleotide binding site on hsp90 was very controversial until x-ray structure of the hsp90 N-terminal domain, showing a nonconventional nucleotide binding site, appeared. A recent study suggested that the hsp90 C-terminal domain also binds ATP (Marcu, M. G., Chadli, A., Bouhouche, I., Catelli, M. G., and Neckers, L. M. (2000) J. Biol. Chem. 275, 37181-37186). In this paper, the interactions of ATP with native hsp90 and its recombinant N-terminal (positions 1-221) and C-terminal (positions 446-728) domains were studied by isothermal titration calorimetry, scanning differential calorimetry, and fluorescence spectroscopy. Results clearly demonstrate that hsp90 possesses a second ATP-binding site located on the C-terminal part of the protein. The association constant between this domain of hsp90 and ATP-Mg and a comparison with the binding constant on the full-length protein are reported for the first time. Secondary structure prediction revealed motifs compatible with a Rossmann fold in the C-terminal part of hsp90. It is proposed that this potential Rossmann fold may constitute the C-terminal ATP-binding site. This work also suggests allosteric interaction between N- and C-terminal domains of hsp90.

Adenosine Triphosphate↗