Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “stability”

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.

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

At least 1,063 records · Page 59Linked to original sources
PubMed2001

The structure and stability of common mental disorders: the NEMESIS study.

BACKGROUND: We analyzed the underlying latent structure of 12-month DSM-III-R diagnoses of 9 common disorders for the general population in the Netherlands. In addition, we sought to establish (1) the stability of the latent structure underlying mental disorders across a 1-year period (structural stability) and (2) the stability of individual differences in mental disorders at the level of the latent dimensions (differential stability). METHODS: Data were obtained from the first and second measurement of the Netherlands Mental Health Survey and Incidence Study (NEMESIS) (response rate at baseline: 69.7%, n = 7076; 1 year later, 79.4%, n = 5618). Nine common DSM-III-R diagnoses were assessed twice with the Composite International Diagnostic Interview with a time lapse of 1 year. Using structural equation modeling, the number of latent dimensions underlying these diagnoses was determined, and the structural and differential stability were assessed. RESULTS: A 3-dimensional model was established as having the best fit: a first dimension underlying substance use disorders (alcohol dependence, drug dependence); a second dimension for mood disorders (major depression, dysthymia), including generalized anxiety disorder; and a third dimension underlying anxiety disorders (simple phobia, social phobia, agoraphobia, and panic disorder). The structural stability of this model during a 1-year period was substantial, and the differential stability of the 3 latent dimensions was considerable. CONCLUSIONS: Our results confirm the 3-dimensional model for 12-month prevalence of mental disorders. Results underline the argument for focusing on core psychopathological processes rather than on their manifestation as distinguished disorders in future population studies on common mental disorders.

Adult↗
PubMed1999

Stabilization of an antibody conjugated with enzyme by 2-methacryloyloxyethyl phosphorylcholine copolymer in enzyme-linked immunosorbent assay.

The purpose of this study was to develop a novel synthetic stabilizer of enzyme-linked antibody in the enzyme-linked immunosorbent assay (ELISA). The water-soluble amphiphilic phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-styrene (St)] was synthesized, and its stabilizing functions for the antibody were compared with conventional stabilizers of the antibody conjugated with enzyme (enzyme-antibody conjugate), such as bovine serum albumin (BSA) and casein. In the absence of the stabilizer, the remaining immunologic activity decreased to about 10% of its initial value after 37 days. The same tendency was observed even when the enzyme-antibody conjugate in 1.0 wt % BSA solution was used as a stabilizer. In 1.0 wt % casein solution, the immunologic activity decreased to 29% of the initial value after 37 days. On the other hand, in 0.1 wt % and 1.0 wt % poly(MPC-co-St) solution, the activity remained 74% and 92% of the initial value, respectively. The effects of poly(MPC-co-St) on the stabilization of the enzyme-antibody conjugate depended on the concentration of poly(MPC-co-St). During the ELISA procedure, not only did poly(MPC-co-St) have no effect on the reaction between the antigen and the antibody, but it also had no effect on the reaction between the enzyme and the substrate. These results indicate that poly(MPC-co-St) has the ability to suppress the denaturation of protein, enzyme, and antibody. We concluded that water-soluble poly(MPC-co-St) is an effective synthetic stabilizer in the ELISA.

Animals↗
PubMed2000

Structural stability of binding sites: consequences for binding affinity and allosteric effects.

During the course of biological function, proteins interact with other proteins, ligands, substrates, inhibitors, etc. These interactions occur at precisely defined locations within the protein but their effects are sometimes propagated to distal regions, triggering highly specific responses. These effects can be used as signals directed to activate or inhibit other sites, modulate interactions with other molecules, and/or establish inter-molecular communication networks. During the past decade, it has become evident that the energy of stabilization of the protein structure is not evenly distributed throughout the molecule and that, under native conditions, proteins lack global cooperativity and are characterized by the occurrence of multiple independent local unfolding events. From a biological point of view, it is important to assess if this uneven distribution reflects specific functional requirements. For example, are binding sites more likely to be found in well structured regions, unstable regions, or mixed regions? In this article, we have addressed these questions by performing a structure-based thermodynamic stability analysis of non-structurally homologous proteins for which high resolution structures of their complexes with specific ligands are available. The results of these studies indicate that for all 16 proteins considered, the binding sites have a dual character and are characterized by the presence of regions with very low structural stability and regions with high stability. In many cases the low stability regions are loops that become stable and cover a significant portion of low molecular weight ligands upon binding. For enzymes, catalytic residues are usually, but not always, located in regions with high structural stability. It is shown that this arrangement provides significant advantages for the optimization of binding affinity of small ligands. In allosteric enzymes, low stability regions in the regulatory site are shown to play a crucial role in the transmission of information to the catalytic site.

Allosteric Regulation↗
PubMed2006

Average assignment method for predicting the stability of protein mutants.

Prediction of protein stability upon amino acid substitutions is an important problem in molecular biology and it will be helpful for designing stable mutants. In this work, we have analyzed the stability of protein mutants using three different data sets of 1791, 1396, and 2204 mutants, respectively, for thermal stability (DeltaTm), free energy change due to thermal (DeltaDeltaG), and denaturant denaturations (DeltaDeltaGH2O), obtained from the ProTherm database. We have classified the mutants into 380 possible substitutions and assigned the stability of each mutant using the information obtained with similar type of mutations. We observed that this assignment could distinguish the stabilizing and destabilizing mutants to an accuracy of 70-80% at different measures of stability. Further, we have classified the mutants based on secondary structure and solvent accessibility (ASA) and observed that the classification significantly improved the accuracy of prediction. The classification of mutants based on helix, strand, and coil distinguished the stabilizing/destabilizing mutants at an average accuracy of 82% and the correlation is 0.56; information about the location of residues at the interior, partially buried, and surface regions of a protein correctly identified the stabilizing/destabilizing residues at an average accuracy of 81% and the correlation is 0.59. The nine subclassifications based on three secondary structures and solvent accessibilities improved the accuracy of assigning stabilizing/destabilizing mutants to an accuracy of 84-89% for the three data sets. Further, the present method is able to predict the free energy change (DeltaDeltaG) upon mutations within a deviation of 0.64 kcal/mol. We suggest that this method could be used for predicting the stability of protein mutants.

Amino Acid Substitution↗
PubMed2001

Characterization of the stability of recombinant protein production in the GS-NS0 expression system.

The GS-NS0 system is an important mammalian expression system used largely within industry for the high-level expression of recombinant proteins for therapeutic use. It is essential that the productivity of this system remains stable throughout culture expansion for the successful long-term production of recombinant proteins. Here we present a study of the stability of recombinant protein production from unamplified GS-NS0 cell lines over extended period of continuous culture. The cell lines used in this study were generated by the transfection of NS0 cells with DNA encoding for a secreted recombinant protein and by two subsequent rounds of limiting dilution cloning prior to analysis of stability. The stability of recombinant protein production was assessed at intervals over a period of 134 days using repeated batch culture in shake flasks. Heterogeneous stability was identified. The productivity of some clones remained consistent throughout 134 days of continuous culture. Others exhibit rapid and progressive loss of productivity. Analysis of the causal relationships underlying stability indicates that the initial transfectant determines the susceptibility to loss or retention of productivity. Selection of production clones on the basis of growth and productivity alone will not predict stability during long-term culture. Our research indicates that stable high-producing clones can readily be obtained from use of the GS-NS0 system in the absence of amplification but there may be molecular features of the original transfectants that could serve as very important predictive indicators of the stability of recombinant protein production.

Animals↗
PubMed2007

Quantitative data on the effects of alkyl substituents and Li-O and Li-N chelation on the stability of secondary alpha-oxy-organolithium compounds.

A DeltaG(eq) stability scale of secondary alpha-oxy-organolithium compounds was established from measurements of tin-lithium exchange equilibria in THF, and the quantitative effects of substituents at the anionic center on carbanion stability are presented. A new lead-lithium exchange equilibrium reaction was also investigated and shown to be a very useful alternative for the determination of the relative stability of the more sterically hindered organolithium compounds. Alkyl groups adversely affect the stability of organolithium compounds when attached to the carbon bearing the negative charge, but the extent of this effect is highly dependent on the nature of the rest of the substituents attached to the anionic center. Quantitative data on the stabilization imparted to organolithium compounds by Li-O and Li-N chelation have been determined for a variety of systems. The formation of four- and five-membered chelate rings leads to a considerable stabilization of the organolithium compound, while chelation through the formation of six-membered rings affords no extra stabilization to this type of organometallics. Multinuclear NMR experiments carried out on several alpha-oxy-organolithium compounds to determine their aggregation state are supportive of these species being monomers in THF solution.

Journal Article↗
PubMed1984

Taxol stabilization of mitotic spindle microtubules: analysis using calcium-induced depolymerization.

Taxol stabilizes or promotes the assembly of microtubules. In this report we characterize the rate, extent, and reversibility of taxol stabilization of calcium-labile microtubules in isolated mitotic spindles, principally from embryos of the sand dollar Echinarachnius parma. The intense depolymerizing action of 100 microM Ca2+ was used to assess the extent of stabilization by taxol. Changes in spindle microtubule assembly were evaluated and recorded by measuring changes in spindle birefringent retardation (BR). Membrane-free mitotic spindles, isolated with a calcium-chelating, nonionic detergent buffer, were stored in an EGTA-glycerol storage buffer to prevent microtubule depolymerization. When perfused with an EGTA-buffer without glycerol, microtubules in these isolated spindles depolymerized gradually over 60-120 min; but in isolated spindles perfused with buffer that contained 100 microM Ca2+, BR decreased by 90% within 2-5 sec. In contrast, spindles that were pretreated for 3 min with 1 microM taxol, or for about 30 sec with 10 microM taxol, lost less than 10% of their initial BR when perfused with buffer containing 100 microM Ca2+. The rate and extent of microtubule stabilization by taxol depended on both the concentration and the duration of exposure to taxol. Taxol stabilization was reversible. After a 15 min preincubation with 1 microM or 10 microM taxol then washout, stability of spindle BR to 100 microM Ca2+ decreased exponentially with a time constant of 30-60 min. Thus taxol dissociates from spindle microtubules at significant rates; taxol-stabilized microtubules are not "fixed."

Alkaloids↗
PubMed1997

Stability and performance of a population pharmacokinetic model.

This study aimed to determine the stability (in terms of covariate selection) of a population pharmacokinetic model and evaluate its performance in the absence of a test data set. Data from 88 full-term infants, 11 of whom were human immunodeficiency virus (HIV)-seropositive, taking an antiinfective agent were analyzed using exploratory data analysis methods and the nonlinear mixed-effects modeling (NONMEM) program to obtain the final population pharmacokinetic model. The stability of the population pharmacokinetic model was tested using the nonparametric bootstrap approach in four steps: 1) with the base pharmacokinetic model, 100 bootstrap replicates of the original data were generated by sampling with replacement; 2) ascertainment that each bootstrap data replicate was described by the basic structural model using the NONMEM objective function; 3) generalized additive modeling (GAM) applied to empiric Bayesian estimates for covariate selection at alpha = 0.05 and a frequency (f) cutoff value of 0.50; and 4) NONMEM population model building using covariates selected in the third step with alpha = 0.005. Performance of the population pharmacokinetic model was evaluated using 200 additional bootstrap replicates of the data by fitting the model obtained in step 4 to them. Parameters obtained were compared with those obtained in the model stability step, and improved prediction error, a measure of predictive accuracy as an index of internal validation, was computed. The reciprocal of serum creatinine (RSC; f = 0.73) and HIV (f = 0.70) were selected by GAM as predictors of clearance (Cl). The population pharmacokinetic model obtained without the determination of model stability included RSC as a predictor of Cl, but the final model from the model stability step included both HIV and RSC as predictors of Cl. Final population pharmacokinetic parameters were obtained with this model fitted to the original data; however, the 95% confidence interval on the HIV status regression coefficient included zero, indicating no significance. The mean parameter estimates obtained with the additional 200 bootstrap replicates of data were within 15% of those obtained with the final model at the regression stability step. Bootstrap resampling procedure is useful for evaluating the stability and performance of a population model by repeatedly fitting it to the bootstrap samples when there is no test data set.

Adolescent↗
PubMed1979

Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. II.

The effect of selected UV stabilizers on the stability of mechanical properties of a polyurethane material, Calthane ND2300, was evaluated. The addition of UV stabilizers prolonged the service life of the systems studied but did not achieve completely satisfactory results. The tensile strength and modulus of elasticity decreased after extended exposure to UV. The rate of decrease, however, was much less for the specimens with UV stabilizers. The polyurethane system that contains a mixture of a UV stabilizer and an antioxidant is considered to be the best of the groups tested, in terms of the percentage of retention of tensile strength and modulus of elasticity. It was also found that elongation at break was increased when the duration of UV aging was increased. This phenomenon occurred in all the systems, with or without UV stabilizers, and can be understood in terms of the concepts of the fragmentation of macromolecules that resulted from UV aging. The physical appearance in conjunction with mechanical property tests are needed to ensure the successful performance of any UV stabilizer.

Chemical Phenomena↗
PubMed2006

Myelin basic protein functions as a microtubule stabilizing protein in differentiated oligodendrocytes.

Myelin basic protein (MBP) is an oligodendrocyte-specific protein essential for oligodendrocyte morphogenesis at late stages of cell differentiation. There is evidence that the morphogenetic function of MBP is mediated by MBP interaction with the cytoskeleton. Thus, an MBP/cytoplasmic microtubule association has been reported, and MBP has Ca(2+)/calmodulin-regulated microtubule cold-stabilizing activity in vitro. However, the unambiguous demonstration of a microtubule-stabilizing activity for MBP in cells has been difficult because oligodendrocytes contain variants of STOP (stable tubule only polypeptide) proteins, which are responsible for microtubule cold stability in different cell types. Herein, we have used genetic mouse models and RNA interference to assay independently the microtubule cold-stabilizing activities of MBP and of STOP in developing oligodendrocytes. In wild-type oligodendrocytes, microtubules were cold stable throughout maturation, which is consistent with the presence of STOP proteins from early stages of differentiation. In contrast, in oligodendrocytes from STOP-deficient mice, microtubules were cold labile in the absence of MBP expression or when MBP expression was restricted to the cell body and became stable in fully differentiated oligodendrocytes, where MBP is expressed in cell extensions. The suppression of MBP by RNA interference in STOP-deficient oligodendrocytes suppressed microtubule cold stability. Additionally, STOP suppression in oligodendrocytes derived from shiverer mice that lack MBP led to the complete suppression of microtubule cold stability at all stages of cell differentiation. These results demonstrate that both STOP and MBP function as microtubule-stabilizing proteins in differentiating oligodendrocytes and could be important for the morphogenetic function of MBP.

Animals↗
PubMed2001

Influence of cationic lipids on the stability and membrane properties of paclitaxel-containing liposomes.

Paclitaxel (taxol) is a poorly soluble anticancer agent that is in widespread clinical use. Liposomes provide a less toxic vehicle for solubilizing the drug and increasing the therapeutic index of paclitaxel in model tumor systems. The role of liposome membrane composition in the stability of paclitaxel-containing formulations is understood partially for neutral and anionic liposomes, but poorly for other compositions. We investigated the effect of dialkyl cationic lipids on the stability and physical properties of paclitaxel-containing liposomes, using circular dichroism (CD), fluorescence spectroscopy, and differential interference contrast microscopy (DIC). DOTAP (1,2-dioleoyl-3-trimethylammonium propane), a cationic lipid used frequently for gene delivery, was combined at various ratios with dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), or distearoylphosphatidylcholine (DSPC). In the absence of DOTAP, the stability of liposomes containing > or =3 mol% paclitaxel was observed to follow the following rank order: DPPC >DSPC > DMPC. Increasing concentrations of DOTAP increased the physical stability of all compositions, and maximal stabilization was achieved at 30-50 mol% DOTAP, depending on the paclitaxel concentration and the acyl chain length of the phosphatidylcholine. The relationship between stability and mole fraction of DOTAP was complex for some compositions. DOTAP exerted a major fluidizing effect on DMPC, DPPC, and DSPC membranes, and the addition of paclitaxel at 3-8 mol% did not increase fluidity further. Studies of membrane phase domain behavior using the probe Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) indicated that both paclitaxel and DOTAP were miscible with the phosphatidylcholine phase. The physical events leading to destabilization of formulations are hypothesized to arise from concentration-dependent paclitaxel self-association rather than immiscibility of the membrane lipids. Given the increased incorporation and stability of paclitaxel in DOTAP-containing membranes and the potential for enhanced interaction with cells, cationic liposomes may provide a therapeutic advantage over previously described liposome formulations.

Antineoplastic Agents, Phytogenic↗
PubMed2004

Comparison of sampling efficiency and storage stability on different sorbents for determination of solvents in occupational air.

This study describes the sampling efficiency and storage stability of compounds typically present in occupational atmospheres on the sorbents Anasorb CSC, Anasorb 747, and Chromosorb 106. The selection of compounds included in the study contained aliphatic and aromatic hydrocarbons, alcohols, esters, glycol ethers, ketones, and halogenated compounds, thus representing a wide range of chemical and physical properties. The different sorbent tubes were simultaneously exposed to the selected compounds as three different mixtures of solvent vapours in air, and storage both at room temperature and at -22 degrees C was investigated. The sorbent tubes were stored and analyzed at two different laboratories. The sampling efficiencies of all the investigated compounds were excellent on Anasorb CSC and Anasorb 747, while Chromosorb 106 did not give such good results for the most volatile compounds under study. The room temperature storage stability on Chromosorb 106, however, was good for all compounds, although formation of artefacts was observed during storage, a disadvantage that was substantially reduced by storage at -22 degrees C. The room temperature storage stability on Anasorb CSC was good for all compounds except some of the ketones. The room temperature storage stability of these ketones, especially cyclohexanone and 2-butanone, was much better on Anasorb 747, which still showed the same excellent storage stability for the remaining compounds. When stored in a freezer, the storage stability of all compounds, including the ketones, was very good on all sorbents. Among the sorbents under study, Anasorb 747 appears to be the most suitable all-round sorbent for monitoring volatile compounds in occupational air, with satisfactory capabilities regarding both sampling efficiency and storage stability.

Air Pollutants, Occupational↗
PubMed1993

Effects of alanine substitutions in alpha-helices of sperm whale myoglobin on protein stability.

The peptide backbones in folded native proteins contain distinctive secondary structures, alpha-helices, beta-sheets, and turns, with significant frequency. One question that arises in folding is how the stability of this secondary structure relates to that of the protein as a whole. To address this question, we substituted the alpha-helix-stabilizing alanine side chain at 16 selected sites in the sequence of sperm whale myoglobin, 12 at helical sites on the surface of the protein, and 4 at obviously internal sites. Substitution of alanine for bulky side chains at internal sites destabilizes the protein, as expected if packing interactions are disrupted. Alanine substitutions do not uniformly stabilize the protein, either in capping positions near the ends of helices or at mid-helical sites near the surface of myoglobin. When corrected for the extent of exposure of each side chain replaced by alanine at a mid-helix position, alanine replacement still has no clear effect in stabilizing the native structure. Thus linkage between the stabilization of secondary structure and tertiary structure in myoglobin cannot be demonstrated, probably because of the relatively small free energy differences between side chains in stabilizing isolated helix. By contrast, about 80% of the variance in free energy observed can be accounted for by the loss in buried surface area of the native residue substituted by alanine. The differential free energy of helix stabilization does not account for any additional variation.

Alanine↗
PubMed1994

Conformational stability of dimeric proteins: quantitative studies by equilibrium denaturation.

The conformational stability of dimeric globular proteins can be measured by equilibrium denaturation studies in solvents such as guanidine hydrochloride or urea. Many dimeric proteins denature with a 2-state equilibrium transition, whereas others have stable intermediates in the process. For those proteins showing a single transition of native dimer to denatured monomer, the conformational stabilities, delta Gu (H2O), range from 10 to 27 kcal/mol, which is significantly greater than the conformational stability found for monomeric proteins. The relative contribution of quaternary interactions to the overall stability of the dimer can be estimated by comparing delta Gu (H2O) from equilibrium denaturation studies to the free energy associated with simple dissociation in the absence of denaturant. In many cases the large stabilization energy of dimers is primarily due to the intersubunit interactions and thus gives a rationale for the formation of oligomers. The magnitude of the conformational stability is related to the size of the polypeptide in the subunit and depends upon the type of structure in the subunit interface. The practical use, interpretation, and utility of estimation of conformational stability of dimers by equilibrium denaturation methods are discussed.

Ligands↗
PubMed2001

Cooperative helix stabilization by complex Arg-Glu salt bridges.

Among the interactions that stabilize the native state of proteins, the role of electrostatic interactions has been difficult to quantify precisely. Surface salt bridges or ion pairs between acidic and basic side chains have only a modest stabilizing effect on the stability of helical peptides or proteins: estimates are roughly 0.5 kcal/mol or less. On the other hand, theoretical arguments and the occurrence of salt bridge networks in thermophilic proteins suggest that multiple salt bridges may exert a stronger stabilizing effect. We show here that triads of charged side chains, Arg(+)-Glu(-)-Arg(+) spaced at i,i+4 or i,i+3 intervals in a helical peptide stabilize alpha helix by more than the additive contribution of two single salt bridges. The free energy of the triad is more than 1 kcal/mol in excess of the sum of the individual pairs, measured in low salt concentration (10 mM). The effect of spacing the three groups is severe; placing the charges at i,i+4 or i,i+3 sites has a strong effect on stability relative to single bridges; other combinations are weaker. A conservative calculation suggests that interactions of this kind between salt bridges can account for much of the stabilization of certain thermophilic proteins.

Alanine↗
PubMed2004

Markovian Backbone Negentropies: Molecular descriptors for protein research. I. Predicting protein stability in Arc repressor mutants.

As more and more protein structures are determined and applied to drug manufacture, there is increasing interest in studying their stability. In this sense, developing novel computational methods to predict and study protein stability in relation to their amino acid sequences has become a significant goal in applied Proteomics. In the study described here, Markovian Backbone Negentropies (MBN) have been introduced in order to model the effect on protein stability of a complete set of alanine substitutions in the Arc repressor. A total of 53 proteins were studied by means of Linear Discriminant Analysis using MBN as molecular descriptors. MBN are molecular descriptors based on a Markov chain model of electron delocalization throughout the protein backbone. The model correctly classified 43 out of 53 (81.13%) proteins according to their thermal stability. More specifically, the model classified 20/28 (71.4%) proteins with near wild-type stability and 23/25 (92%) proteins with reduced stability. Moreover, the model presented a good Mathew's regression coefficient of 0.643. Validation of the model was carried out by several Jackknife procedures. The method compares favorably with surface-dependent and thermodynamic parameter stability scoring functions. For instance, the D-FIRE potential classification function shows a level of good classification of 76.9%. On the other hand, surface, volume, logP, and molar refractivity show accuracies of 70.7, 62.3, 59.0, and 60.0%, respectively.

Alanine↗
PubMed2005

The role of calcium in the conformational dynamics and thermal stability of the D-galactose/D-glucose-binding protein from Escherichia coli.

We have characterized stability and conformational dynamics of the calcium depleted D-galactose/D-glucose-binding protein (GGBP) from Escherichia coli. The structural stability of the protein was investigated by steady state and time resolved fluorescence, and far-UV circular dichroism in the temperature range from 20 degrees C to 70 degrees C. We have found that the absence of the Ca(2+) ion results in a significant destabilization of the C-terminal domain of the protein. In particular, the melting temperature decreases by about 10 degrees C with the simultaneous loss of the melting cooperativity. Time resolved fluorescence quenching revealed significant loosening of the protein when highly shielded Trp residue(s) became accessible to acrylamide at higher temperatures. We have documented a significant stabilizing effect of glucose that mostly reverts the effect of calcium, that is, the thermal stability of the protein increases by about 10 degrees C and the melting cooperativity is restored. Moreover, the protein structure remains compact with low amplitude of the segmental mobility up to high temperatures. We have used molecular dynamics to identify the structural feature responsible for changes in the temperature stability. Disintegration of the Ca(2+)-binding loop seems to be responsible for the loss of the stability in the absence of calcium. The new insights on the structural properties and temperature stability of the calcium depleted GGBP contribute to better understanding of the protein function and constitute important information for the development of new biotechnological applications of this class of proteins.

Binding Sites↗
PubMed1986

Stabilization of the ribonuclease S-peptide alpha-helix by trifluoroethanol.

The effects of trifluoroethanol (TFE) on the stability of the alpha-helix formed by ribonuclease S-peptide, residues 1-19 of ribonuclease A, were studied by measuring circular dichroism as a function of TFE concentration, pH, and temperature. The S-peptide forms an unusually stable alpha-helix, which is known to be stabilized by TFE. The magnitude of the effect of charged groups on the peptide, manifested by the change in alpha-helix stability as a function of pH, was not altered significantly by either TFE concentration or temperature, indicating that the lower dielectric constant of TFE is not important in the stabilization of this alpha-helix. This suggests that the alpha-helix might be stabilized by many interactions in addition to the effects of charges. The titration curve of circular dichroism vs. TFE concentration appears to be cooperative at 0 degree C, but becomes progressively less cooperative at temperatures between 25 and 75 degrees C. The properties of the TFE stabilization indicate that TFE might be a useful probe with which to measure the stability of marginally stable peptides and small proteins.

Circular Dichroism↗