Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Stability analysis”

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 1,693 records · Page 94Linked to original sources
PubMed1983

Drinking water and drug dosage in rat studies.

Spontaneously hypertensive rats were treated with verapamil, hydralazine, indapamide or bepridil added to their drinking water. These substances had most different effects on the water consumption of the animals, displaying both positive and negative feed-back mechanisms. Furthermore there were considerable differences in stability of the drugs in solution. It is therefore concluded that continuous control of water intake and analysis of the stability of the drug is essential for the establishment of proper dose-response relationships.

Animals↗
PubMedDate not supplied

Analyte stability study of N-methylcarbamate pesticides in beef and poultry liver tissues by liquid chromatography.

To optimize conditions for sample collection, preparation, storage, and analysis and to assure the validity of our previously published liquid chromatographic (LC) method for carbamate analysis in tissue, stabilities of 16 N-methylcarbamates in beef, duck, and chicken liver tissues were studied by using 2 sampling protocols. Tissue samples were fortified at room temperature to a concentration 5 to 10 times greater than either the Environmental Protection Agency tolerance level for each compound (if established) or the concentration used in the previously published method. Thereafter, samples were continuously frozen at -4 degrees C for varying time intervals. In the first study, samples were analyzed one day (initial) and 0.5, 1, 1.5, 2, 3, 4, 5, and 6 months after fortification. In the second study, samples were analyzed one day (initial) and 0.5, 1, 2, 3, and 6 months after fortification. For each residue and species, a minimum of 4 samples were analyzed by LC at each point in time, and the mean represented analyte concentration at the end of each time interval. Rates of residue depletion varied among analytes and among species. Depletion rates were greater in duck livers than in beef livers. Methomyl and oxamyl were depleted completely within 2 weeks. Between 2 and 6 months after sample fortification, residue depletions to levels below detection limits were observed for aldicarb, aldicarb sulfoxide, aldicarb sulfone, dioxacarb, promecarb, propoxur, and bendiocarb. The initial loss of certain carbamates during sample preparation in tissues exposed to room temperature for up to 8 h was greater than the subsequent rate of loss. Results indicate that cryogenic conditions are required for sample preparation and storage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Resonance frequency analysis measurements of implants at placement surgery.

PURPOSE: The knowledge of what levels of primary stability can be obtained in different jawbone regions and of what factors influence primary stability is limited. The objective of this study was to evaluate primary stability by resonance frequency analysis (RFA) measurements of implants placed according to a surgical protocol that aimed for high primary stability. The aim was also to correlate RFA measurements with factors related to the surgical technique, the patient, and implant design. MATERIALS AND METHODS: A total of 905 Brånemark dental implants used in 267 consecutive patients were measured with RFA at the time of placement surgery. RESULTS: A mean ISQ value of 67.4 (SD 8.6) was obtained for all implants. Univariate analyses with the implant or patient as unit showed higher ISQ values in men compared with women, in mandibles compared with maxillae, in posterior compared with anterior sites, and for wide-platform implants in comparison with regular/narrow-platform implants. There was a correlation between bone quality and primary stability, with lower ISQ values obtained for implants placed in softer bone. A lower stability was seen with increased implant length. A stepwise multiple regression analysis using the patient as unit showed that jaw type and gender had independent effects on primary stability. CONCLUSION: The results suggest that factors related to bone density and implant diameter/length may affect the level of primary implant stability. Furthermore, greater stability was observed in male than in female patients. High primary implant stability was achieved in all jaw regions, although the use of thinner drills and/or tapered implants cannot fully compensate for the effect of soft bone. The research design does not permit conclusions regarding long-term treatment outcome with implants.

Aged↗
PubMed2004

[Primary stability of cement free hip cup prostheses--morphometric comparative analysis of two cup types].

An uncemented implanted acetabular cup must ensure primary stability and postoperative osteointegration. For both conditions the immediate postoperative contact between bone and the structured surface of the cup is of decisive importance. Two different types of acetabular cups manufactured by ESKA (standard model and Kapuziner model) were implanted in the innominate bones of elderly deceased persons. After plastination, thin serial sections were obtained. On the basis of X-rays of these sections, contact between bone and the reticulate surface of the cups was quantified. The quality of the contact was analysed densitometrically.

Aged↗
PubMed2003

Human plasma high-density lipoproteins are stabilized by kinetic factors.

High-density lipoproteins (HDL) are heterogeneous complexes of proteins and lipids that mediate cholesterol removal from the body. Our thermal and chemical denaturation studies of mature spherical HDL isolated from human plasma show that, contrary to the widely held assumption, the particle stability has a kinetic rather than thermodynamic origin. Guanidinum hydrochloride (GdmHCl) concentration jumps at 25 degrees C monitored by circular dichroism (CD) at 222 nm reveal two dominant irreversible kinetic phases in HDL denaturation. The slower phase (relaxation time tau(1) approximately 2 x 10(4) seconds) is observed in 1-6 M GdmHCl, and the faster phase (tau(2) approximately 2 x 10(3) seconds) is detected in 3-6 M GdmHCl. Comparison of the free energy barriers associated with these phases, deltaG* = 16-17 kcal mol(-1), with the near-zero apparent thermodynamic stability inferred from the spectroscopic measurements after prolonged incubation in 0-6 M GdmHCl at 22 degrees C indicates the kinetic origin for HDL stabilization. Electron microscopic analysis of HDL incubated in 0-6 M GdmHCl suggests that the slower kinetic phase involves HDL fusion, while the faster phase involves particle rupture and release of the apolar lipid core. Thermal denaturation experiments indicate high enthalpic barriers for the particle rupture that may arise from the transient disruption of lipid and/or protein packing interactions. These results corroborate our earlier analysis of model discoidal HDL and indicate that a kinetic mechanism provides a universal natural strategy for lipoprotein stabilization. Such a mechanism may facilitate structural integrity of the heterogeneous lipoprotein particles, slow their spontaneous interconversions, and thereby modulate lipoprotein lifetime and functions.

Circular Dichroism↗
PubMed2002

Multiple thiol-anchor capped DNA-gold nanoparticle conjugates.

We report the synthesis of a novel trithiol-capped oligodeoxyribonucleotide and gold nanoparticle conjugates prepared from it. These DNA-gold nanoparticle conjugates exhibit substantially higher stability than analogs prepared from monothiol and cyclic disulfide-capped oligodeoxyribonucleotides, but comparable hybridization properties. A quantitative analysis of their stability under a range of conditions is provided. Significantly, this novel trithiol oligodeoxyribonucleotide can be used to stabilize particles >30 nm in diameter, which are essential for many diagnostic applications.

DNA↗
PubMed1998

Quantitative structure-function and structure-stability relationships of purposely modified proteins.

Quantitative structure-function relationships (QSFR) and quantitative structure-stability relationships (QSSR) analyses are described here. The objective of these analyses is to investigate and quantitatively describe the effect of the changes in structure of protein on its function or stability. During the analysis, the structural and physico-chemical properties of the amino acid residues are related to activity or stability data derived for the group of proteins containing systematic substitutions at certain positions. Four examples of the application of these analyses on the data obtained with proteins modified by site-directed mutagenesis experiments are provided. Structure-function relationships were studied for 15 mutants in position 172 of the haloalkane dehalogenase and 19 mutants in position 222 of the subtilisin, while the structure-stability relationships were investigated for 13 mutants in position 157 of phage T4 lysozyme and 18 mutants in position 49 of alpha-subunits tryptophan synthase. A total of 402 molecular descriptors derived from AAindex database were used to quantify amino acid properties and the multivariate statistical technique--partial least squares projections to latent structures--was used to identify those of them which are important for explanation of the activity and stability data. Quantitative models were developed and internally validated for every data set. The possibilities for further development of both analyses and their application for predictive and analytical purposes in protein engineering research are discussed.

Glutamic Acid↗
PubMed2002

Cost-effectiveness comparison of salmeterol/fluticasone propionate versus montelukast in the treatment of adults with persistent asthma.

OBJECTIVE: To compare the relative cost effectiveness of salmeterol (50 microg)/ fluticasone propionate (100 microg) with that of oral montelukast (10mg) as initial maintenance therapy in patients with persistent asthma uncontrolled on short-acting beta2-agonist therapy alone. STUDY DESIGN: A cost-effectiveness analysis was performed based on effectiveness and resource utilisation data that was prospectively collected from a randomised, double-blind, double-dummy, 12-week trial. PATIENTS AND METHODS: Patients (>15 years of age) who had asthma for at least 6 months. Effectiveness measurements in this analysis included improvement in forced expiratory volume in 1 second (FEV(1)) and symptom-free days (SFDs). Cost of asthma drug treatment as well as costs related to an asthma exacerbation were used in the cost analysis. The study assumed a payer's perspective. All costs are in 2001 US dollars. RESULTS: Of the 423 patients eligible for the study, 211 were randomised to salmeterol/fluticasone propionate and 212 to montelukast. Treatment with salmeterol/fluticasone propionate resulted in a significantly higher proportion of patients who achieved a 12% increase in FEV(1) (successful treatment) [salmeterol/fluticasone propionate: 71% vs montelukast: 39%; p < 0.001] and percentage of SFDs (salmeterol/fluticasone propionate: 46.8% vs montelukast: 21.5%; p < 0.001) compared with montelukast. The mean daily costs per successfully treated patient were lower in the salmeterol/fluticasone propionate group (US dollars 5.03, 95% CI US dollars 4.61 to US dollars 5.50) compared with the montelukast group (US dollars 8.25, 95% CI US dollars 6.98 to US dollars 9.93). Furthermore, per patient mean daily cost per SFD was lower with salmeterol/fluticasone propionate (US dollars 7.63, 95% CI US dollars 6.90 to US dollars 8.50) compared with montelukast (US dollars 14.89, 95% CI US dollars 12.36 to US dollars 17.98). Incremental cost-effectiveness ratios (ICERs) showed that the additional costs to achieve these benefits with salmeterol/fluticasone propionate were minimal. With regards to improvement in lung function, the ICER was US dollars 1.33 (95% CI US dollars 0.80 to US dollars 2.02) and with regards to SFD, the ICER was US dollars 1.69 (95% CI US dollars 1.01 to US dollars 2.48). Sensitivity analysis demonstrated the stability of the results over a range of assumptions. CONCLUSIONS: From a third-party payer perspective, this analysis shows that based on increased efficacy and only a slight increase in cost, twice-daily treatment with salmeterol/fluticasone propionate is more cost effective than once-daily treatment with montelukast as initial maintenance therapy for persistent asthma. This finding complements the results of the clinical analyses indicating that treatment of both inflammation and bronchoconstriction with products such as salmeterol/ fluticasone propionate may be more cost effective as initial maintenance asthma therapy than the use of leukotriene modifiers such as montelukast.

Acetates↗
PubMedDate not supplied

"Torso rotation" experiments; 3: Effects of acute changes in vestibular function on the control of voluntary head movements.

"Torso Rotation" (TR) produces an acute, reversible change in human vestibular function. Experiments were performed to determine if repeated exposure to this technique would result in long-term adaptive modifications. In one experiment, VOR gain was evaluated. Measurements were obtained before and 3 times after 30 minutes of TR, on 7 consecutive days. VOR gain dropped each day after TR, returning to normal within about 20 min. In a separate experiment with different subjects, eyes-open gaze stability was measured during voluntary head shaking between 3.0 and 0.3 Hz. The same test schedule was used. Analysis of gaze stability (limited to frequencies between 1.0 and 2.0 Hz) was complicated by an unexpected finding. Despite careful instructions, head displacement increased each day after TR, also returning to normal within about 20 min. Surprisingly, subjects were unaware of this change. Combining the 2 experiments, VOR gain and head amplitude were averaged across all 7 days, separately for the 4 daily tests. Head amplitude was plotted against VOR gain for these 4 averages. Amplitude was greater when VOR gain was reduced, with a remarkably high correlation (R2 = 0.996). These findings confirm that vestibular feedback plays an important role in the control of voluntary head movement. Furthermore, the data suggest that instability of the visual scene reported by subjects shaking their heads after TR resulted not only from a lower VOR gain, but also from the inadvertent use of higher head velocities.

Female↗
PubMed2005

Functional characterization and ATP-induced dimerization of the isolated ABC-domain of the haemolysin B transporter.

Nucleotide-binding domains (NBD) are highly conserved constituents of ATP-binding cassette (ABC) transporters. Members of this family couple ATP hydrolysis to the transfer of various molecules across cell membranes. The NBD of the HlyB transporter, HlyB-NBD, was characterized with respect to its uncoupled ATPase activity, oligomeric state, and stability in solution. Experimental data showed that both the nature and pH of an assay buffer influenced the level of protein activity. Comparative analysis of protein stability and ATPase activity in various buffers suggests an inverse relationship between the two. The highest ATPase activity was detected in HEPES, pH 7.0. A kinetic analysis of the ATPase activity in this buffer revealed an enzyme concentration dependence and ATP-induced protein oligomerization. Assuming that the dimer is the active form of enzyme, at least half of the purified HlyB-NBD was estimated to be a dimer at 1.2 microM under the most optimal conditions for ATP hydrolysis. This is about 2 orders of magnitude lower than reported for other canonical ABC-ATPases. The maximum reaction velocity of 0.6 micromol/mg x min at 22 degrees C and the apparent kinetic constant K(app)(0.5) of 0.26 mM for ATP were determined for the dimerized HlyB-NBD. Gel filtration experiments with the wild-type protein and HlyB-NBD mutated in a key catalytic residue, H662A, provided further evidence for ATP-induced protein dimerization. ATPase activity experiments with protein mixtures composed of wild-type and the ATPase-deficient H662A mutant demonstrated that one intact NBD within a dimer is sufficient for ATP hydrolysis. This single site turnover might suggest a sequential mechanism of ATP hydrolysis in the intact HlyB transporter.

ATP-Binding Cassette Transporters↗
PubMed1992

Physicochemical properties of oxamniquine indicate a new polymorphic form.

New dissolution rate, chemical stability and thermal analysis data are reported for an anti-schistosomal drug, oxamniquine. A slow dissolution rate (40-70% in 1 h) was found, which may contribute to its erratic clinical response. The drug was found to be chemically stable in water for at least 21 days at 37 degrees C. Dissolution rate and thermal analysis evidence is presented for a previously unreported polymorph (Form III). This form appears to be intermediate in physical stability between the known Forms I and II.

Chemical Phenomena↗
PubMed1984

Design and analysis of accelerated degradation tests for the stability of biological standards III. Principles of design.

The principles of designing an accelerated degradation test for a biological standard are considered, with special emphasis on ensuring accuracy and precision of the predicted low temperature degradation rate. A three-stage design is proposed which initially monitors samples at the highest of the elevated temperatures, but which switches attention progressively to the lower temperatures as degradation begins to be detected. The advantages of this design over one where testing is carried out after a predetermined period are that it is (i) more efficient, (ii) more reliable and (iii) better suited to test the assumptions which underly the analysis of the results. Consideration is also given to additional checks which can be made on the stability of biological standards and to methods of monitoring long-term stability after the standard has been set up.

Biological Products↗
PubMed1982

Albumin stabilizes leukotriene A4.

Chemical analysis of intact leukotriene A4 showed that vertebrate albumins prolonged its aqueous half-life. At pH 7.4, leukotriene A4 hydrolyzed by first order reaction kinetics with rate constants inversely proportional to the albumin concentration. The stabilizing effect of albumin varied quantitatively among different species. Certain agents, such as warfarin, that interact with the site I binding region of albumin reversed its stabilizing effect. Sequestration and exposure of leukotriene A4 to a hydrophobic, alkaline microenvironment of albumin would account for the results. The amino acid sequences Lys-Ala-Trp-Ala-Val-Ala-Arg from residues 211-217 of human albumin or Lys-Ala-Trp-Ser-Val-Ala-Arg from residues 210-216 of bovine albumin are compatible with this requirement. The persistence of leukotriene A4 in the presence of albumin confirms and extends our recent observations on its uniform and predictable influence on eicosanoid stability. The significance of this influence is uncertain; however, albumin can no longer be viewed as inert considering its capacity to modify the stability of several, structurally diverse eicosanoids.

Animals↗
PubMed1981

Thermal stability of proteins analyzed by temperature scanning pH-stat titration.

Based on the fact that pH changes occur during the thermal unfolding of a protein, a pH-stat titrimetric procedure is described for the analysis of thermal stability. In all cases the agreement with other stability measurements was good, including a correlation with activity loss in enzymes. A model for the titration curves, assuming first-order denaturation kinetics, linear temperature increase, and validity of the Arrhenius equation, has been proposed and analyzed. Thus, thermodynamic constants can be calculated from titration curves, or transition temperatures estimation if the Arrhenius constants are known. The equipment consists of a pH-stat, a programmable heating unit, and a temperature measuring/recording system. Analysis can be done quickly and on partially purified solutions, provided the buffer capacity is low, using about 20 mg protein/10 ml sample. The effects of pH, Ca2+ ions, substrate, chemical modification, etc., on thermal stability are conveniently analyzed up to about 90 degrees C.

Calcium↗
PubMed2005

The manganese-stabilizing protein is required for photosystem II assembly/stability and photoautotrophy in higher plants.

Interfering RNA was used to suppress the expression of two genes that encode the manganese-stabilizing protein of photosystem II in Arabidopsis thaliana, MSP-1 (encoded by psbO-1, At5g66570), and MSP-2 (encoded by psbO-2, At3g50820). A phenotypic series of transgenic plants was recovered that expressed high, intermediate, and low amounts of these two manganese-stabilizing proteins. Chlorophyll fluorescence induction and decay analyses were performed. Decreasing amounts of expressed protein led to the progressive loss of variable fluorescence and a marked decrease in the fluorescence quantum yield (F(v)/F(m)) in both the absence and the presence of dichloromethylurea. This result indicated that the amount of functional photosystem II reaction centers was compromised in the plants that exhibited intermediate and low amounts of the manganese-stabilizing proteins. An analysis of the decay of the variable fluorescence in the presence of dichlorophenyldimethylurea indicated that charge recombination between Q ((A-)) and the S(2) state of the oxygen-evolving complex was seriously retarded in the plants that expressed low amounts of the manganese stabilizing proteins. This may have indicated a stabilization of the S(2) state in the absence of the extrinsic component. Immunological analysis of the photosystem II protein complement indicated that significant losses of the CP47, CP43, and D1 proteins occurred upon the loss of the manganese-stabilizing proteins. This indicated that these extrinsic proteins were required for photosystem II core assembly/stability. Additionally, although the quantity of the 24-kDa extrinsic protein was only modestly affected by the loss of the manganese-stabilizing proteins, the 17-kDa extrinsic protein dramatically decreased. The control proteins ribulose bisphosphate carboxylase and cytochrome f were not affected by the loss of the manganese-stabilizing proteins; the photosystem I PsaB protein, however, was significantly reduced in the low expressing transgenic plants. Finally, it was determined that the transgenic plants that expressed low amounts of the manganese-stabilizing proteins could not grow photoautotrophically.

Arabidopsis↗
PubMed1965

DETERMINATION OF STEAM-VOLATILE ORGANIC ACIDS IN FERMENTATION MEDIA BY GAS-LIQUID CHROMATOGRAPHY.

Five gas chromatographic liquid phases (25% Carbowax 20 M plus 4% H(3)PO(4), 17.5% dioctyl sebacate plus 7.5% sebacic acid, 17.5% dioctyl sebacate plus 7.5% docosanoic acid, 5% Tween 80, and 20% LAC-296 [poly (diethylene glycol adipate)] plus 2% H(3)PO(4)) were studied with respect to their utility in the separation and quantitation of steam-volatile organic acids commonly produced in fermentation. Optimal operating conditions and column stability for routine analysis were established. An Aerograph Hy-Fi gas chromatograph was used for all work, except the studies with Tween 80 in which an Aerograph A-90-C was employed. Chromatographic traces are presented of volatile fatty acid analyses with each of the liquid phases. Complete separation of all isomers of the fatty acids from C(2) to C(5) was accomplished by the Carbowax 20 M plus H(3)PO(4), dioctyl sebacate plus sebacic acid, and dioctyl sebacate plus docosanoic acid columns. The latter two liquid phases were extremely unstable and proved to be unsatisfactory for analysis of aqueous samples. A column of Carbowax 20 M + H(3)PO(4) separated steam-volatile organic acids completely. The volatile fatty acid isomers were separated by 5% Tween 80 somewhat less completely, and the peak shapes were not as sharp and symmetrical as that desired for good quantitative work. LAC-296 (20%) plus 2% H(3)PO(4) proved to be the most satisfactory of the liquid phases for routine analysis of deproteinated in vitro rumen fermentation media. The column has been used for routine analysis of rumen fermentation fluid and in vitro rumen incubation fluid. All the organic acids from C(2) to C(5), except isobutyric, could be quantitated with this column. Stability of the column with the aqueous solutions was extremely good. The standard deviation of the analysis of each volatile acid component in a fermentation fluid was less than 0.5 molar per cent. The short-chain organic acids (C(2) to C(5)) were shown to be extremely stable in aqueous solution for as long as 6 months after preparation for gas chromatographic analysis by protein precipitation with metaphosphoric acid-H(2)SO(4) and refrigeration at 4 C in stoppered tubes.

Animals↗
PubMed1998

Conformational stability and thermodynamics of folding of ribonucleases Sa, Sa2 and Sa3.

Ribonucleases Sa, Sa2, and Sa3 are three small, extracellular enzymes produced by different strains of Streptomyces aureofaciens with amino acid sequences that are 50% identical. We have studied the unfolding of these enzymes by heat and urea to determine the conformational stability and its dependence on temperature, pH, NaCl, and the disulfide bond. All three of the Sa ribonucleases unfold reversibly by a two-state mechanism with melting temperatures, Tm, at pH 7 of 48.4 degrees C (Sa), 41.1 degrees C (Sa2), and 47.2 degrees C (Sa3). The Tm values are increased in the presence of 0.5 M NaCl by 4.0 deg. C (Sa), 0.1 deg. C (Sa2), and 7.2 deg. C (Sa3). The Tm values are decreased by 20.0 deg. C (Sa), 31.5 deg. C (Sa2), and 27.0 deg. C (Sa3) when the single disulfide bond in the molecules is reduced. We compare these results with similar studies on two other members of the microbial ribonuclease family, RNase T1 and RNase Ba (barnase), and with a member of the mammalian ribonuclease family, RNase A. At pH 7 and 25 degrees C, the conformational stabilities of the ribonucleases are (kcal/mol): 2.9 (Sa2), 5.6 (Sa3), 6.1 (Sa), 6.6 (T1), 8.7 (Ba), and 9.2 (A). Our analysis of the stabilizing forces suggests that the hydrophobic effect contributes from 90 to 110 kcal/mol and that hydrogen bonding contributes from 70 to 105 kcal/mol to the stability of these ribonucleases. Thus, we think that the hydrophobic effect and hydrogen bonding make large but comparable contributions to the conformational stability of these proteins.

Amino Acid Sequence↗