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PubMed2001

Increasing the hydrophobic interaction between terminal W-motifs enhances the stability of Salmonella typhimurium sialidase. A general strategy for the stabilization of beta-propeller protein fold.

Protein engineering of the beta-propeller protein aimed at enhancing the structural stability of the protein was carried out using a monomeric single domain beta-propeller protein, Salmonella typhimurium sialidase, as a model. Ala53 and Ala69 each located at strands B and C of the W1 motif were mutated to Leu and Val, respectively, to increase the hydrophobic interaction between W1 and W6 motifs. The mutants showed enhanced stability towards guanidine hydrochloride and thermal unfolding. Ala53Leu showed higher stability, probably owing to the capability of the mutated Leu to interact extensively with more residues involved in the hydrophobic interactions between the terminal W-motifs. The mutations, which are located far from the active site, have no significant effect on the enzymatic properties. The strategy to enhance the stability proposed here might be applied to the other beta-propeller proteins.

Alanine↗
PubMed1979

In vitro stability of nitrate reductase from wheat leaves: I. Stability of highly purified enzyme and its component activities.

NADH-nitrate reductase has been highly purified from leaves of 8-day-old wheat (Triticum aestivum L. cv. Olympic) seedlings by affinity chromatography, using blue dextran-Sepharose 4B. Purification was assessed by polyacrylamide gel electrophoresis. The enzyme was isolated with a specific activity of 23 micromoles nitrite produced per minute per milligram protein at 25 C. At pH 7.5, the optimum pH for stability of NADH-nitrate reductase, this enzyme, and a component enzyme reduced flavin adenine mononucleotide (FMNH(2))-nitrate reductase has a similar stability at both 10 and 25 C. Two other component enzymes-methylviologen-nitrate reductase and NADH-ferricyanide reductase-also have a similar but higher stability. At this pH the Arrhenius plot for decay of NADH-nitrate reductase and methylviologen-nitrate reductase indicates a transition temperature at approximately 30 C above which the energy of activation for denaturation increases. FMNH(2)-nitrate reductase and NADH-ferricyanide reductase do now show this transition. The energy of activation for denaturation (approximately 9 kcal per mole) of each enzyme is similar between 15 and 30 C. The optimum pH for stability of the component enzymes was: NADH-ferricyanide reductase, 6.6; FMNH(2)-nitrate reductase and methylviologen-nitrate reductase, 8.9. All of our studies indicate that the NADH-ferricyanide reductase was the most stable component of the purified nitrate reductase (at pH 6.6, t((1/2)) [25 C] = 704 minutes). Data are presented which suggest that methylviologen and FMNH(2) do not donate electrons to the same site of the nitrate reductase protein.

Journal Article↗
PubMed1976

Light-absorbing properties, stability, and spectral stabilization of indocyanine green.

The absorption spectrum of indocyanine green depends on the nature of the solvent medium and on the dye concentration. Binding to plasma proteins causes the principal peaks in the absorption spectrum to shift about 25 nm toward the higher wavelengths. The much greater influence on the spectrum of the dye concentration results from progressive aggregate formation with increasing concentration. Indocyanine green solutions therefore do not follow Lambert-Beer's law above 15 mg-I-1 (in plasma). Indocyanine green solutions in plasma and concentrated (1,000 mg-I-1) solutions in distilled water are stable for at least 4 h. In long-term experiments the optical density of indocyanine green solutions in plasma as well as in distilled water generally diminishes, even in the dark. On the 7th day a new absorption maximum starts to appear at gamma=900 nm, possibly caused by further aggregate formation leading to much larger particles. Spectral stabilization after injection of a concentrated solution into the blood is most rapid when the dye is dissolved in distilled water. Spectral stabilization slows down with decreasing temperature. As rapid spectral stabilization is essential in quantitative dye dilution studies, the practice of adding a albumin and/or isotonic saline solution to the injectate should be discontinued. When a 10 g-1(-1) aqueous solution of indocyanine green is used, spectral stabilization takes less than 1.5 a (at 37 degrees C), which is sufficiently fast for almost any application.

Blood↗
PubMed2000

Double-blind comparison of addition of a second mood stabilizer versus an antidepressant to an initial mood stabilizer for treatment of patients with bipolar depression.

OBJECTIVE: This study's purpose was to clarify the appropriate treatment of bipolar depression by comparing the addition of an antidepressant versus a second mood stabilizer for inpatients being treated with lithium carbonate or divalproex sodium. METHOD: Twenty-seven patients were randomly assigned to groups that received double-blind treatment with paroxetine or a second mood stabilizer (lithium carbonate or divalproex sodium) for 6 weeks. RESULTS: Both groups showed significant improvement in depressive symptoms during the 6-week trial. There were significantly more noncompleters in the group being treated with the two mood stabilizers than in the group being treated with a mood stabilizer and paroxetine. CONCLUSIONS: Both treatments appeared to be effective; however, the addition of an antidepressant may have greater clinical utility in the treatment of bipolar depression.

Adult↗
PubMed2002

Biomechanical evaluation of immediate stability with rectangular versus cylindrical interbody cages in stabilization of the lumbar spine.

BACKGROUND: Recent cadaver studies show stability against axial rotation with a cylindrical cage is marginally superior to a rectangular cage. The purpose of this biomechanical study in cadaver spine was to evaluate the stability of a new rectangular titanium cage design, which has teeth similar to the threads of cylindrical cages to engage the endplates. METHODS: Ten motion segments (five L2-3, five L4-5) were tested. From each cadaver spine, one motion segment was fixed with a pair of cylindrical cages (BAK, Sulzer Medica) and the other with paired rectangular cages (Rotafix, Corin Spinal). Each specimen was tested in an unconstrained state, after cage introduction and after additional posterior translaminar screw fixation. The range of motion (ROM) in flexion-extension, lateral bending, and rotation was tested in a materials testing machine, with +/- 5 Nm cyclical load over 10 sec per cycle; data from the third cycle was captured for analysis. RESULTS: ROM in all directions was significantly reduced (p < 0.05) with both types of cages. There was no significant difference in reduction of ROM in flexion-extension (p = 0.6) and rotation (p = 0.92) between the two cage groups, but stability in lateral bending was marginally superior with the rectangular cages (p = 0.11). Additional posterior fixation further reduced the ROM significantly (p < 0.05) in most directions in both cage groups, but did not show any difference between the cage groups. CONCLUSIONS: There was no significant difference in immediate stability in any direction between the threaded cylindrical cage and the new design of the rectangular cage with endplate teeth.

Journal Article↗
PubMed1994

Tau confers drug stability but not cold stability to microtubules in living cells.

We previously defined two classes of microtubule polymer in the axons of cultured sympathetic neurons that differ in their sensitivity to nocodazole by roughly 35-fold (Baas and Black (1990) J. Cell Biol. 111, 495-509). Here we demonstrate that virtually all of the microtubule polymer in these axons, including the drug-labile polymer, is stable to cold. What factors account for the unique stability properties of axonal microtubules? In the present study, we have focused on the role of tau, a microtubule-associated protein that is highly enriched in the axon, in determining the stability of microtubules to nocodazole and/or cold in living cells. We used a baculovirus vector to express very high levels of tau in insect ovarian Sf9 cells. The cells respond by extending processes that contain dense bundles of microtubules (Knops et al. (1991) J. Cell Biol. 114, 725-734). Cells induced to express tau were treated with either cold or 2 micrograms/ml nocodazole for times ranging from 5 minutes to 6 hours. The results with each treatment were very different from one another. Virtually all of the polymer was depolymerized within the first 30 minutes in cold, while little or no microtubule depolymerization was detected even after 6 hours in nocodazole. Based on these results, we conclude that tau is almost certainly a factor in conferring drug stability to axonal microtubules, but that factors other than or in addition to tau are required to confer cold stability.

Animals↗
PubMed1988

Structure-stability relationship in proteins: fundamental tasks and strategy for the development of stabilized enzyme catalysts for biotechnology.

The problem of relationships between the protein structure and its stability comprises two major questions. First, how to elucidate the peculiarities of the protein structure responsible for its stability. Second, knowing the general molecular basis of protein stability, how to change the structure of a given protein in order to increase its stability. This review is an attempt to show the modern state of the first (fundamental) and the second (applied) aspects of the problem.

Bacterial Proteins↗
PubMed1999

Immediate stabilization of unstable pelvic fractures versus delayed stabilization.

To compare the immediate and long term outcome of immediate stabilization of the unstable pelvic fractures to delayed stabilization with simple external fixation, the study was carried out as a paralell trial with 2 year follow-up. There were 112 patients with 69 males and 43 females who had unstable pelvic fractures. They were allocated randomly into 2 groups. In group 1, 40 patients, conventional management was performed while in group 2, 72 patients, reduction and anterior stabilization of pelvic fractures with a simple external fixator were carried out immediately just after the unstable fractures were detected. Blood transfusion, post operative pain, need of reconstructive surgery of the pelvic fractures and late deformities were less in the group 2. Immediate anterior reduction and stabilization of the unstable pelvic fractures gave encouraging results.

Adult↗
PubMed2002

Evaluation of the stability of aneurysms after embolization using detachable coils: correlation between stability of aneurysms and embolized volume of aneurysms.

BACKGROUND AND PURPOSE: The long-term outcome of aneurysmal coil embolization has not been determined. We retrospectively analyzed the results of our cases treated with detachable coils and evaluated the long-term stability of embolized aneurysms. METHODS: This study involved 100 aneurysms in 93 patients who underwent follow-up angiography > or = 3 months after initial treatment between December 1993 and December 1999. The percentage of the coil volume occupying the aneurysm lumen (embolized volume) was used as an index to evaluate the stability of embolized aneurysms. The reliability of the embolized volume was also evaluated by comparing angiographic percentage occlusion. RESULTS: Follow-up angiographic assessment was conducted 12 +/- 8.5 months after initial treatment. Angiographic evaluation of percentage occlusion at initial treatment did not always predict long-term stability of embolized aneurysms. Of 49 aneurysms judged as being totally occluded at initial treatment, 44 remained unchanged and five showed recanalization. The embolized volume of unchanged aneurysms was 30.8 +/- 10.2%, and that of recanalized aneurysms was 19.9 +/- 10.6%. There was a significant difference between these two groups (P=.03). Of 29 subtotally occluded aneurysms, nine had further thrombosis (embolized volume = 31.8 +/- 12.7%), nine remained unchanged (embolized volume = 23.2 +/- 10.3%), and 11 had recanalization (embolized volume = 14.1 +/- 6.1%). The mean embolized volume of 11 recanalized aneurysms was significantly lower than in the thrombosed group and the unchanged group (P=.002 and P <.001, respectively). Large aneurysms tended to have recanalization more frequently (59%) than did small aneurysms (15%). CONCLUSION: There is a significant correlation between embolized volume and stability of embolized aneurysms. Embolized volume is a more objective index than is subjectively angiographic percentage occlusion. In addition to angiographic assessment, measurement of embolized volume could be useful to predict angiographic changes of aneurysms.

Adult↗
PubMedDate not supplied

[The dual stabilizing and destabilizing effect of decylamine on DNA structure and stability].

The influence of decylamine on DNA structure and stability has been studied from the changes in UV-spectra and UV-melting curves. It was found that at low concentrations, the aliphatic amine stabilizes the double helix while at high concentrations, on the contrary, the amine disturbs it. The interaction of aliphatic amine with DNA results in a sharp increase in the heterogeneity of thermostability of different sites of the double helix. The stabilizing effect of aliphatic amines is connected with a decrease in repealing between negatively charged sugar-phosphate chains of the double helix, while the destabilizing effect is the result of displacement of intramolecular base-base hydrogen bonds by intermolecular base-amine H-bonds. The biological significance of the dual, stabilizing and destabilizing effects of aliphatic amines on DNA helix is shown.

Amines↗
PubMed2001

Thermal stability of human ferritin: concentration dependence and enhanced stability of an N-terminal fusion mutant.

Though human L-chain ferritin has been known to be more resistant to physical denaturation than H-type ferritin, its stability characteristics and kinetic information have not been reported in detail. Overexpressed recombinant ferritin (FTN) in Escherichia coli formed inclusion bodies through noncovalent molecular interaction and easily dissolved with regaining the iron-uptake activity by a simple pH-shift process at high protein concentration (>600 mg l(-1)). FTN was relatively thermostable at low protein concentration (0.2 g l(-1)), but it became extremely thermolabile at high protein concentration (1.3 g l(-1)), i.e., more than 80% of FTN was coprecipitated within 5 min under the same heat-induced denaturation condition. Aggregation rate constant for initial 5 min at high protein concentration was 6.04 x 10(-3) s(-1) for FTN. Surprisingly, glucagon. ferritin mutant (GFTN), consisting of an N-terminus fusion partner, human glucagon (29-residue alpha-helical peptide), showed significantly enhanced thermal stability even at high protein concentration. That is, in spite of 40-min heat treatment, more than 50% of GFTN the still remained soluble with maintaining the same functional properties. The aggregation rate constants were 2.75 x 10(-4) and 2.80 x 10(-4) s(-1) at low and high concentration, respectively, for GFTN. These results suggest a critical participation of the N-terminal domain of ferritin in the temperature-induced aggregation pathway. Presumably, partially denatured amino terminus of FTN is involved in nonspecific molecular interaction resulting in the off-pathway aggregation. It is notable that the purified GFTN showed the same molar capacity of iron (Fe(+3)) storage as standard ferritin. From the analysis of fluorescence emission spectrum, the physical stability of GFTN was also very comparable to that of standard ferritin under the various denaturation conditions induced by GdnHCl.

Drug Stability↗
PubMed1996

The alpha-helix of ribonuclease T1 as an independent stability unit: direct comparison of peptide and protein stability.

Measurements of the change in conformational stability, delta(delta G), upon mutation of two acidic residues at the C terminus of the helix of ribonuclease T1 have recently been reported. Here, we investigate peptides based on the sequence of the helix with the same mutations: Glu28 replaced with Gln, Asp29 replaced with Asn, and the double mutant. In addition, the mutant Lys25 to Gln was studied. Changes in helix content of the peptides with pH confirm the conclusion found in the intact protein, that the charged forms of the acidic residues destabilize the protein by destabilizing the helix. The pH-dependence of the change in conformational free energy for the peptides and mutant proteins show fair correspondence for D29N and the double mutant. The mutants E28Q and K25Q, on the other hand, give striking agreement between the protein and peptide systems. This agreement suggests that the helix of ribonuclease T1 behaves as an independently stabilized structural unit of the intact protein and that stabilization of the helical form of the peptide is mirrored in the protein.

Amino Acid Sequence↗
PubMed1993

Chemical stability of liposomes: implications for their physical stability.

In the first part of this article, chemical and physical stability of aqueous liposome dispersions have been addressed. Chemical stability of phospholipids has been considered in two parts: oxidation and hydrolysis. Major attention has been paid to hydrolysis kinetics of phospholipids as a function of pH, temperature, buffer concentration and ionic strength. Furthermore, the effect of chain length, head group, state of aggregation, addition of cholesterol and presence of charge on the hydrolysis kinetics of phospholipids has been dealt with. In the second part physical stability of chemically degraded liposome dispersions has been evaluated. In the final part quality control assays for liposome dispersions is presented and a HPLC method with a refractive index detector for the analysis of phospholipids from aqueous liposome dispersions is described.

Drug Stability↗
PubMed1996

Stabilization of Octastatin, a somatostatin analogue: comparative accelerated stability studies of two formulations for freeze-dried products.

Octastatin (vapreotide INN) is a somatostatin analogue being developed in gastro-enterologic, neuroendocrine and oncologic applications. The pharmaceutical form is a freeze-dried preparation for parental injection use. This study was intended to evaluate the stability of the freeze-dried products and to determine the optimally stable formulation. Two types of stabilizing agents (lactose and glutamic acid/sodium glutamate buffer) and three dosage forms (0.5, 1.5, 15 mg of vapreotide base) were investigated. The peptide content and chemical stability of cakes stored at 50 degrees C and 70% relative humidity were determined by HPLC and the regression analysis parameters calculated. Results indicate that the formulation with glutamate buffer is appropriate for long term storage.

Antineoplastic Agents↗
PubMed1998

Protein stability function relations: beta-lactoglobulin-A sulphydryl group reactivity and its relationship to protein unfolding stability.

The effect of protein stability on the reactivity of the free sulphydryl (SH) group in beta-lactoglobulin-A (beta-LgA) provides a model for the study of protein stability-function relations (PSFR). The free energy change for protein unfolding (delta G(o)) and SH group exposure (delta GSH) were determined from (i) the urea unfolding curve for beta-LgA and (ii) the kinetics of beta-LgA SH/disulphide exchange with 2-pyridine disulphide (2-PDS) in 0-8 M urea (pH 3). Protein unfolding profiles determined from extrinsic fluorescence and SH-group reactivity measurements were not coincident. beta-LgA formed a stable intermediate (X) state in the presence of 4 M urea with delta G(o) = 20 (+/- 0.03) kJ/mol. From the low rate of SH/disulphide exchange in 4 M urea, the SH-group within beta-LgA was efficiently masked within the X-state. SH reactivity increased after beta-LgA was unfolded in 6-8 M urea with, delta GSH = 43(+/- 6.4) kJ/mol. Such results are discussed in terms of possible interrelationships between protein unfolding stability and SH reactivity in beta-LgA.

Drug Stability↗
PubMed1999

Validation of a high-performance liquid chromatographic method for the determination of norfloxacin and its application to stability studies (photo-stability study of norfloxacin).

The development and validation study of a sensitive, rapid, reproducible, easy and precise reversed-phase high-performance liquid chromatographic assay for norfloxacin (NFLX) samples from photo-stability of solid dosage forms, without using gradient elution, extraction methods and without using counter-ion has been carried out. The method showed excellent linearity (r2> or =0.999) in the range 1-20 microg ml(-1) using a Lichrosorb-RP-8 column (10 microm, 20 cm x 4.6 mm) and UV-detection (278 nm) at ambient temperature. This method showed good efficiency for the analysis of photodegraded NFLX samples, and was applied to study the photo-stability of NFLX tablets under different conditions (direct sun light, ultraviolet light and fluorescent light). It was proven that the use of a disintegrant can increase the photo-stability of the NFLX in the tablets. This effect was studied in directly compressible tablets with microcrystalline cellulose (MCC) and mannitol for direct compression.

Anti-Infective Agents↗
PubMed1998

Stability study of fotemustine in PVC infusion bags and sets under various conditions using a stability-indicating high-performance liquid chromatographic assay.

The stability and compatibility of fotemustine, a nitrosourea anticancer agent, in 5% dextrose solution with polyvinyl chloride (PVC) containers and administration sets were studied under different conditions of temperature and light. The drug was diluted to 0.8 and 2 mg ml(-1) in 100 or 250 ml 5% dextrose injection solutions for 1-h simulated infusions using PVC bags and administration sets with protection from light. After preparation in the PVC bags containing 5% dextrose, fotemustine was also prepared at the same concentrations and stored at 4 degrees C for 48 h and at room temperature (22 degrees C) or at sunray exposure ( > 30 degrees C) over 8 h with or without protection from light. The solution samples were removed immediately at various time points of simulated infusions and storage, and stored at -20 degrees C until analysis. The physical compatibility with PVC and chemical stability in solution of fotemustine were assessed by visual examination and by measuring the concentration of the drug in duplicate using a stability-indicating high-performance chromatographic assay. When admixed with a 5% dextrose solution, fotemustine 2 and 0.8 mg ml(-1) was compatible and stable over 1-h of simulated infusion using PVC bags through PVC administration sets with protection from light. On the other hand, in the same diluent, fotemustine was compatible and stable with PVC bags for at least 8 h at 22 degrees C with protection from light and for at least 48 h at 4 degrees C with protection from light. There were no pH variation, no visual change, no color change, no visible precipitation and no loss of the drug. Conversely, when the solutions were exposed to light (ambient or solar), the drug concentration decreased rapidly, leading to the production of a degradation product as shown by mass spectral analysis and a discoloration of the solutions. Finally, in all cases, no DEHP (di-2-ethylhexyl phthalate) was detected in the injection solution.

Chromatography, High Pressure Liquid↗
PubMed1994

Stabilities of nucleotide loops bridging the pyrimidine strands in DNA pyrimidine.purine.pyrimidine triplexes: special stability of the CTTTG loop.

Recent studies of DNA hairpin loops have shown considerable dependence of the stability on the sequence of the loop [Senior, M., Jones, R. A., & Breslauer, K. J. (1988a) Proc. Natl. Acad. Sci. U.S.A. 85, 6242-6246; Xodo, L. E., Manzini, G., Quadrifoglio, F., van der Marel, G., & van Boom, J. H. (1989) Biochimie 71, 793-803; Hirao, I., Nishimura, Y., Tagawa, Y., Watanabe, K., & Miura, K. (1992) Nucleic Acids Res. 20, 3891-3896]. Analogous studies have not, until now, been carried out with loops in triple helices. We report the results from experiments in which we examine the relative stabilities of pentanucleotide loops that bridge between the pyrimidine strands in DNA pyr.pur.pyr triple helices. There are two types of loops that are defined by the relative orientation of the purine strand: a 5'-loop and a 3'-loop. The sequences examined in this study are the bimolecular triplexes formed between 5'-dTTCTTTTCL1TTTL5CTTTTCTT (loop nucleotides are underlined, and L1 and L5 represent varied nucleotides) and the two purine strands, 5'-dAAGAAAAG-3' and 5'-dGAAAAGAA-3'. The first and last nucleotides in the loop are varied, since stacking interactions may be strongest at these positions [Senior et al., 1988a; Senior, M., Jones, R. A., & Breslauer, K. J. (1988b) Biochemistry 27, 3879-3885], and we examine 14 sequence combinations for each loop type. Thermal denaturation studies carried out at pH 7.0 indicate considerable variation in the stabilities of these loops.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗