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PubMed2005

Influence of environmental stresses on stability of O/W emulsions containing cationic droplets stabilized by SDS-fish gelatin membranes.

Oil-in-water (O/W) emulsions containing small oil droplets (d32 approximately 0.22 microm) stabilized by sodium dodecyl sulfate (SDS)-fish gelatin (FG) membranes were produced by an electrostatic deposition technique. A primary emulsion containing anionic SDS-coated droplets (zeta approximately -40 mV) was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (20 wt % corn oil, 0.46 wt % SDS, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic SDS-FG-coated droplets (zeta approximately +30 mV) was formed by diluting the primary emulsion with an aqueous fish gelatin solution (10 wt % corn oil, 0.23 wt % SDS, 100 mM acetic acid, 2.00 wt % fish gelatin, pH 3.0). The stabilities of primary and secondary emulsions with the same oil concentration to thermal processing, ionic strength, and pH were assessed by measuring particle size distribution, zeta potential, microstructure, destabilized oil, and creaming stability. The droplets in secondary emulsions had good stability to droplet aggregation at holding temperatures from 30 to 90 degrees C for 30 min, [NaCl] < or = 100 mM, and pH values from 3 to 8. This study shows that the ability to generate emulsions containing droplets stabilized by multilayer interfacial membranes comprised of two or more types of emulsifiers, rather than a single interfacial layer comprised of one type of emulsifier, may lead to the development of food products with improved stability to environmental stresses.

Animals↗
PubMed2004

Investigating conformational stability of bovine pancreatic phospholipase A2: a novel concept in evaluating the contribution of the 'native-framework' of disulphides to the global conformational stability of proteins.

Bovine pancreatic PLA(2) (phospholipase A(2)) is a 14 kDa protein whose structure is highly cross-linked by seven disulphide bonds. We investigated the structural stability of this enzyme by the method of 'disulphide-scrambling' with denaturants such as urea, GdmCl (guanidine hydrochloride), GdmSCN (guanidine thiocyanate) and at high temperatures in the presence of 2-mercaptoethanol (0.2 mM) as thiol initiator. Reverse-phase HPLC was used to follow denaturation. To denature 50% of the native protein, 1.25 M GdmSCN, approx. 3 M GdmCl and higher than 8 M urea were required. Only 20% of the protein was denatured after 2 h at 60 degrees C, whereas complete denaturation was seen after 2 h at 70 degrees C and within 30 min at 80 degrees C. A distinct enhancement of stability was observed when denaturation was conducted in the presence of 10 mM calcium chloride, which has not been reported previously. CD studies of GdmCl denaturation of bovine PLA(2) showed that 2.5 M GdmCl was required to denature 50% of the protein in the presence of 0.2 mM 2-mercaptoethanol (in agreement with the HPLC analysis), whereas 6.4 M GdmCl was necessary to denature 50% of the protein in the absence of a thiol initiator. Conformational stability (Delta G (water)) was estimated to be 8.7 kcal/mol (1 cal=4.184 J) by 'disulphide-intact' denaturation (where 'native' disulphide framework was unaffected) and 2.5 kcal/mol by 'disulphide-scrambling' denaturation (involved breaking of native disulphides and formation of 'non-native' ones). The difference, Delta(Delta G (water)), of 6.2 kcal/mol was the conformational stability contributed by the 'native-framework' of seven disulphides. Using bovine PLA(2) as an example, we have demonstrated a novel comparative technique, where the conformational stability study of a disulphide-containing protein, with a common denaturant, in both the presence and absence of catalytic amounts of a thiol initiator can be used as a convenient method to estimate selectively and quantitatively the actual contribution of the 'native disulphide bond network' towards the global conformational stability of the protein.

Animals↗
PubMed2001

Osmolytes stabilize ribonuclease S by stabilizing its fragments S protein and S peptide to compact folding-competent states.

Osmolytes stabilize proteins to thermal and chemical denaturation. We have studied the effects of the osmolytes sarcosine, betaine, trimethylamine-N-oxide, and taurine on the structure and stability of the protein.peptide complex RNase S using x-ray crystallography and titration calorimetry, respectively. The largest degree of stabilization is achieved with 6 m sarcosine, which increases the denaturation temperatures of RNase S and S pro by 24.6 and 17.4 degrees C, respectively, at pH 5 and protects both proteins against tryptic cleavage. Four crystal structures of RNase S in the presence of different osmolytes do not offer any evidence for osmolyte binding to the folded state of the protein or any perturbation in the water structure surrounding the protein. The degree of stabilization in 6 m sarcosine increases with temperature, ranging from -0.52 kcal mol(-1) at 20 degrees C to -5.4 kcal mol(-1) at 60 degrees C. The data support the thesis that osmolytes that stabilize proteins, do so by perturbing unfolded states, which change conformation to a compact, folding competent state in the presence of osmolyte. The increased stabilization thus results from a decrease in conformational entropy of the unfolded state.

Amino Acid Sequence↗
PubMed1995

Occurrence, solution structure and stability of DNA hairpins stabilized by a GA/CG helix unit.

The occurrence and NMR solution structure of a class of biloop hairpins containing the sequence 5'-CGXYAG are presented. These hairpins, which are variations on a sequence found in the reverse transcript of the human T-cell leukemia virus 2 (HLV2), show elevated melting points and high chemical stability toward denaturation by urea. Hairpins with the 5'-CGXYAG configuration have melting points 18-20 degrees higher than hairpins with 5'-CAXYGG or 5'-GGXYAC configurations. The identities of the looping bases, X and Y above, play a negligible role in determining the stability of this DNA hairpin stability. This is very different from G-A based loops in RNA, where the third base must be a purine for high stability [the GNRA loops; V.P. Antao, S.Y. Lai and I. Tinoco, Jr (1991) Nucleic Acids Res., 19, 5901-5905]. We show that these properties are associated with a four base helix unit that contains both a sheared GA base pair and a Watson-Crick CG base pair upon which it is stacked. As an understanding of the significance of AG base pairs has become increasingly important in the structural biology of nucleic acids, we compute an 0.7-0.9 A precision ensemble of NMR solution structures using iterative relaxation matrix methods. Calculations performed on NMR-derived structures indicate that neither base-base electrostatic interactions, nor base-solvent dispersive interactions, are significant factors in determining the observed differences in hairpin stability. Thus the stability of the 5'-CGXYAG configuration would appear to derive from favorable base-base London/van der Waals interactions.

Base Composition↗
PubMed2003

How can free energy component analysis explain the difference in protein stability caused by amino acid substitutions? Effect of three hydrophobic mutations at the 56th residue on the stability of human lysozyme.

To elucidate the molecular mechanism of thermal stability, it is essential to determine what are the major free energy components that contribute significantly to the total free energy difference caused by amino acid mutations. In this work, we carried out free energy calculations based on all-atom molecular dynamics simulations to investigate the effect of three hydrophobic mutations at the same position, I56A, I56V and I56F of human lysozyme. The calculated free energy differences are in good agreement with the experimental values in all cases. From free energy component analysis, we found that small changes in stability in the I56A and I56V mutants originate from the short-range Lennard-Jones interactions, whereas the I56F mutant is largely destabilized owing to the changes in the long-range electrostatic interactions. The calculated results are also compared with the free energy components determined by an empirical relationship based on the native-state structure and thermodynamic data. Although this relationship has been shown to be very successful in reproducing the stability changes caused by various amino acid substitutions in several proteins, the changes of stability in I56V and I56F mutants are not reproduced very well. By comparing the free energy components calculated by these two approaches, we showed that the effect of the long-range interaction on the stability changes may be underestimated in the empirical relationships when the structural change caused by mutation is relatively small, as in I56F. It is also suggested that estimation of the change in accessible surface area, deltadeltaASA, may be overestimated if the structure around the mutation site in the denatured state is native-like, which would cause overestimation of the free energy change as in the case of I56V. Our results clearly show that the combined approach of the free energy calculation based on the all-atom molecular dynamics simulation and the empirical relationships is very useful for understanding the detailed mechanism of protein stability.

Amino Acid Substitution↗
PubMed2005

Oligomerization endows enormous stability to soybean agglutinin: a comparison of the stability of monomer and tetramer of soybean agglutinin.

Soybean agglutinin is a tetrameric legume lectin, each of whose subunits are glycosylated. This protein shows a very high degree of stability when compared to the other proteins of the same family. In a previous work, it was shown that the unusual stability of the protein is due to a high degree of subunit interactions. In this study we present the thermodynamic parameters for the stability of soybean agglutinin monomer. The monomeric species is found at pH 2 and below which it is most populated at pH 1.9, as evident from size-exclusion chromatographic and dynamic light scattering studies. The analyses of circular dichroism and fluorescence spectroscopy suggest that the monomer is well folded, and that it has certain characteristic features when compared to its tetrameric counterpart. The conformational stabilities of the tetramer and the monomer at the temperature of their maximum stabilities (310 K) are 59.2 kcal/mol and 9.8 kcal/mol, respectively, indicating that oligomerization contributes significantly to the stability of the native molecule. Also, the T(g) difference for the two forms of the protein is approximately 40 K, whereas the difference in DeltaC(p) is only 1.6 kcal/mol/K. This suggests that the major hydrophobic core is present in the monomer itself, and that oligomerization involves mainly ionic interactions.

Biophysical Phenomena↗
PubMed2005

Stabilizing the stabilizer: group psychoeducation enhances the stability of serum lithium levels.

OBJECTIVE: To determine the effect on the serum lithium levels of a psychoeducational program in patients with bipolar disorder. METHOD: This is a subanalysis of data obtained from a larger study on the efficacy of group psychoeducation in the prophylaxis of recurrences in bipolar disorders. Data on plasma lithium levels were obtained at five time points: baseline, 6, 12, 18 and 24 months. Serum lithium levels of patients who had received psychoeduction (psychoeducated) (N = 49) and non-psychoeducated patients (N = 44) were compared. RESULTS: Mean serum lithium levels were significantly higher and more stable for the psychoeducation group. CONCLUSIONS: As changes in serum lithium level may be a powerful predictor of recurrence for bipolar patients, the addition of group psychoeducation to standard pharmacological treatment may be beneficial to optimize serum lithium levels and, thereby improve outcome.

Adult↗
PubMed1997

A hypothesis to explain why translation inhibitors stabilize mRNAs in mammalian cells: mRNA stability and mitosis.

Protein synthesis inhibitors prolong the half-lives of most mRNAs at least fourfold in the somatic cells of higher eukaryotes and in yeast cells. Some mRNAs are stabilized because the inhibitors affect mRNA-specific regulatory factors; however, hundreds or thousands of other mRNAs are probably stabilized by a common mechanism. We propose that mRNA stabilization in cells treated with a translation inhibitor reflects a physiological process that occurs during each mitosis and is important for cell survival. Transcription and translation rates decline drastically during a 1-2 hour interval of mitosis. We hypothesize that translational repression during this interval somehow inactivates a critical component of the mRNA degradation machinery. As a result, mRNA half-lives are prolonged during the interval when transcription is repressed. If labile mRNAs were not stabilized during mitosis they, and perhaps also the labile proteins they encode, would be depleted as the cell entered G1 phase, with deleterious consequences. Stabilization during mitosis, or in response to translation inhibitors, thus preserves the capacity of the cell to synthesize essential proteins as it enters G1 or recovers from inhibitor treatment. mRNA stabilization might serve a similar purpose during starvation or any stress negatively affecting translation.

Animals↗
PubMed2006

Mitochondrial replication origin stability and propensity of adjacent tRNA genes to form putative replication origins increase developmental stability in lizards.

Secondary structure stability of mitochondrial origins of light-strand replication (OL) presumably reduces delayed formation of light-strand initiating replication forks on the heavy strand. Delayed replication initiation prolongs single strandedness of the heavy strand. More mutations accumulate during the prolonged time spent single stranded. Presumably, delayed replication initiation and excess mutations affect mitochondrial biochemical processes and ultimately morphological outcomes of development at the whole-organism level. This predicts that developmental stability increases with OL secondary structure stability and with formation of OL-like structures by the five tRNA genes flanking recognized OLs. Stable OLs and high percentages of OL-resembling secondary structures of adjacent tRNA genes (predicted by Mfold) correlate positively with developmental stability in three lizard families (Anguidae, Amphisbaenidae, and Polychrotidae). Accounting for effects of the regular OL, Sfold-predicted OL-like propensity of the entire tRNA gene cluster (not of individual genes) correlates with increased developmental stability in Anguidae, also across the entire free-energy range of Boltzmann's distribution of secondary structures. In the fossorial Amphisbaenidae, the OL-like structure-forming propensity of tRNA genes correlates positively with developmental stability for the distribution's sub-optimally stable regions, and negatively for its optimally stable regions, suggesting the thermoregulated functioning of OL vs. flanking tRNA genes as replication origins. Results for polychrotid tRNA genes are intermediate. Anguid tRNA genes possibly function in addition to the regular OL. Mitochondrial tRNA genes may thus frequently acquire and lose the alternative OL function, without sequence (gene) duplication and loss of their primary function.

Animals↗
PubMed2000

Colloidal Platinum Nanoparticles Stabilized by Vinyl Polymers with Amide Side Chains: Dispersion Stability and Catalytic Activity in Aqueous Electrolyte Solutions.

Colloidal platinum nanoparticles were prepared by ethanol reduction of PtCl(6)(2-) in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA), or poly(N-vinylisobuty-ramide) (PNVIBA). The effects of molecular weight and molar ratio of monomeric unit/Pt on the particle sizes and size distributions were characterized by transmission electron microscopy and UV-visible spectroscopy. The flocculation behavior of the polymer-stabilized colloidal Pt nanoparticles was studied with respect to the effects of temperature, addition of inorganic salts, and composition of the mixed solvents. The dispersion stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt<PNVIBA-Pt<PVP-Pt<PNVA-Pt<PNVF-Pt. Anions of the added salts played an essential role in reducing the dispersion stability and sulfates were more efficient at promoting flocculation than chlorides. The PNVF-Pt colloids did not show any critical flocculation point (temperature or salt concentration) under employed conditions, owing to the strongly hydrophilic nature of PNVF chains. The catalytic activity of PNVF-Pt colloids for hydrogenation of allyl alcohol in 0.8 M Na(2)SO(4) solution was the same as that in pure water. Copyright 2000 Academic Press.

Journal Article↗
PubMed1995

Intrinsic stability of individual alpha helices modulates structure and stability of the apomyoglobin molten globule form.

During acid-induced unfolding of apomyoglobin, a partly folded form is observed at pH values of around four. In this form, the A, G and H helices are folded, while the rest of the molecule, including the B helix, demonstrates little structure. The partly folded form has been described as a molten globule form. To determine the factors that govern the structure and stability of this form, we introduced two helix-stabilizing mutations into the B helix, and tested their effect on the structure and stability of both the native form and the molten globule form. We show that the two Gly-->Ala replacements in the B helix produce altered fluorescence and CD properties of the partly folded intermediate, a result which implies that the B helix has become part of the structured region of the molten globule form. The helix content of a model peptide containing the sequence of the B helix is increased by the G-->A replacements, as is the helix content of the molten globule intermediate, whereas the stability and the helix content of the native protein are not altered. The observed increase in helicity is larger in the folding intermediate than in the model peptide, suggesting that nonspecific interactions, such as the hydrophobic interactions exhibited by the entire polypeptide chain, amplify the effect of intrinsic helix stability. The overall results suggest that the intrinsic stability of each individual helix is a factor in deciding whether or not that helix becomes part of the structured molten globule.

Alanine↗
PubMed2004

Postural stabilization from fingertip contact: I. Variations in sway attenuation, perceived stability and contact forces with aging.

In this study, we compared the ability of young (n=10, 19-32 years) and older subjects (n=35, 60-86 years) to use fingertip contact as a balance aid during quiet stance under various conditions to determine whether aging would influence contact strategies. Experimental trials (duration, 60 s) included two visual conditions (vision; no vision), three fingertip contact conditions (no touch; smooth touch; rough touch) and two support surface conditions (firm; foam). In trials with contact, participants were required to maintain a light contact with their right index fingertip on an instrumented touch-plate. Subjects were not constrained to exert minimal contact force, although they were aware that the touch-plate was not designed for physical support. From displacements of the centre of foot pressure (COP), mean sway amplitude (MSA) was computed in the anterior-posterior (COP(AP)) and medio-lateral (COP(ML)) directions. Subjective estimates of stability were also obtained by asking participants to rate perceived stability on a visual analog scale in each condition. Mean normal force (FN) and mean resultant tangential force (F(TAN)) were computed from contact force data applied on the touch plate. In both age groups, touch conditions had a substantial effect on MSA in the AP direction under both support surface conditions, with reductions averaging between 40-55% when touch was allowed. Reductions in the ML direction, though less important (8-12% on average), were nevertheless highly significant, especially in the older subjects when standing on the foam. In the two groups, vision and texture had only marginal impact on MSA computed on both support surfaces. Contrasting with sway measurements, stability ratings were highly influenced by visual conditions in both age groups. Only in conditions of deficient support (foam surface) and absent vision did the perceived effect of touch exceed that of vision. Age had a major impact, however, on contact forces deployed during trials with touch. While individuals in the young group typically produced forces of <1 N (mean FN, 0.32+/-0.15 N) to achieve postural stabilization, older subjects tended to use higher, though not too excessive, contact forces (mean FN, 1.21+/-0.75 N) under the same conditions. From these findings, we conclude that the ability to use contact cues from the fingertip as a source of sensory information to improve postural stability is largely preserved in healthy older adults. The increase in contact force deployed by older individuals to achieve postural stabilization is interpreted as a compensatory strategy to help overcome age-related loss in tactile sensation, an issue that will be further addressed in a companion paper.

Adult↗
PubMed2005

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal.

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

Animals↗
PubMed2006

Evaluation of therapeutic potentials of site-specific PEGylated glucagon-like peptide-1 isomers as a type 2 anti-diabetic treatment: Insulinotropic activity, glucose-stabilizing capability, and proteolytic stability.

PEGylation has been considered to be a good biotechnique for improving the therapeutic value of glucagon-like peptide-1 (GLP-1) analogs for the treatment of type 2 diabetes. Despite the attractive anti-diabetic potentials, GLP-1 does not exert its full biological action because of its extremely short life-time in vivo due to rapid proteolytic degradation. Here, the enzyme-resistant mono-PEGylated GLP-1 isomers substituted at Lys(26)- or Lys(34)-amine were prepared through a newly devised site-specific PEGylation process using a maleic anhydride-protection/deprotection method. The therapeutic potentials of these site-specific PEGylated GLP-1 isomers (Lys(26)- or Lys(34)-PEG-GLP-1) along with His(7)-(N-terminus) PEG-GLP-1 were evaluated by examining their insulinotropic activity, glucose-stabilizing capability, and proteolytic stability. Lys(34)-PEG-GLP-1 was found to have the well-preserved insulinotropic activity (93% efficacy versus GLP-1) in isolated rat pancreatic islets. Furthermore, Lys(34)-PEG-GLP-1 showed the most prominent glucose-stabilizing capability, evaluated via an oral glucose tolerance test in db/db mice by considering the following three crucial factors: (i) maximum blood glucose level (BGL), (ii) required time to lower the BGL below 100mg/dl, and (iii) total hypoglycemic degree. Additionally, Lys(34)-PEG-GLP-1 had longer half-lives than the other PEGylated GLP-1s in the dipeptidyl peptidase IV (DPP IV) inhibitor-treated liver or kidney homogenate, and its stability against DPP IV was also comparable to that of Lys(26)-PEG-GLP-1. Taken together, Lys(34)-PEG-GLP-1 displayed the promising characteristics in all evaluations versus His(7)- or Lys(26)-PEG-GLP-1. This site-specific PEGylated GLP-1 analog would have therapeutic usefulness for treating type 2 diabetes on account of the well-preserved insulinotropic activity, the increased proteolytic stability, and thereby the improved glucose-stabilizing capability.

Animals↗
PubMed2006

Effect of 2,4-D contamination on soil functional stability evaluated using the relative soil stability index (RSSI).

Soil functional stability is the capacity of soil functions to resist and recover from an environmental perturbation and can be used to evaluate soil health. It can be influenced by the presence of xenobiotics such as herbicides. The impact of a fresh 2,4-D contamination (36 mg kg(-1) dry soil) on soil functional stability was evaluated by comparing the capacity of soil enzyme activities to resist and recover from a heat perturbation for both a clean and 2,4-D-contaminated soil. The functional stabilities of the soils (uniform sands, pH 6.9, 7% (w/w) organic matter) were calculated using the relative soil stability index (RSSI). The RSSI scores indicate the proportion of potential enzyme activity the soil retains after a perturbation compared to the potential activity of an unperturbed soil. Six extra-cellular enzyme activities (acid and alkaline phosphatases, arylsulfatase, urease, protease and beta-glucosidase) were monitored in soil microcosms during a 15-day period. During this period, a 60 degrees C heat perturbation was applied to the soil for 24 h. The activities of arylsulfatase and protease were found to be the most stable following heat perturbation obtaining the highest RSSI scores (87% and 77%, respectively). Urease activity showed the lowest RSSI score (38%). Although all enzyme activities were inhibited by the presence of 2,4-D, the RSSI results indicated that contamination lowered the stability of only three enzyme activities (arylsulfatase, beta-glucosidase and urease). The RSSI adequately described resistance, recovery and recovery rate parameters and enabled differentiation between functional stabilities of clean and contaminated soil and between different soil types.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2006

Theoretical estimation of stability ratios for hexadecane-in-water (H/W) emulsions stabilized with nonylphenol ethoxylated surfactants.

The effect of steric interactions on the stability of oil-in-water emulsions is studied here by means of emulsion stability simulations (ESS). For this purpose, a new steric potential based on a modification of the one formerly proposed by Vincent et. al. is employed. The parameters of the calculation correspond to hexadecane in water emulsions stabilized with nonylphenol ethoxylated surfactants of different chain lengths (NPEm). Stability ratios (W) were calculated using the half life time of the number of drops per unit volume of these systems. A functional relationship between W and the repulsive potential barrier, (DeltaV), similar to the one previously found by Prieve and Ruckenstein for electrostatically stabilized suspensions was obtained. However, according to our simulations there exists a threshold for the stability of emulsions with respect to coalescence which is approximately located around 12.7 k(B)T.

Journal Article↗