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PubMedDate not supplied

Analysis, purification and stability: requirements for a metabolism study of an azo dye and pigment.

Impurities of aromatic amines in the azo dye and pigment, Direct Black 38 and Pigment Yellow 12, and in vitro stability of the dye were determined. These factors can affect the results of studies designed to ascertain whether the two compounds are metabolized to potential carcinogens in hamsters. Procedures for removing impurities from the two compounds are also presented. Electron-capture gas chromatography of the heptafluorobutyryl derivatives of the impurities and degradation products was used to satisfy all the analytical requirements of the experiments. Major impurities found in Direct Black 28 were benzidine, 4-aminobiphenyl and 2,4-diaminoazobenzene; whereas, only 3,3'-dichlorobenzidine was found in Pigment Yellow 12. Stability studies of the purified dye conducted in water and in urine from hamsters and humans indicated that the dye would not degrade under the conditions used for collecting and assaying samples from a metabolism experiment. However, within 48 hours at 25 and 37.5 degrees C, the dye did degrade to known carcinogens in both hamster and human urine. Such degradation not only points out the need for proper storage of samples from metabolism studies but suggests that industrial effluents containing the dye should be properly treated before release into the environment.

3,3'-Dichlorobenzidine↗
PubMed1997

Analysis of the stabilization of hen lysozyme by helix macrodipole and charged side chain interaction.

In the N-terminal region of the alpha-helix of the c-type lysozymes, two Asx residues exist at the 18th and 27th positions. Hen lysozyme has Asp18/Asn27 (18D/27N), and we prepared three mutant lysozymes, Asn18/Asn27 (18N/27N), Asn18/Asp27 (18N/27D), and Asp18/Asp27 (18D/27D). The stability of the wild-type (18D/27N) lysozyme supported the existence of a hydrogen bond between the side chain of Asp18 and the amide group at the N1 position in the alpha-helix, while the stability of the 18N/27D lysozyme supported the presence of the capping box between the Ser24 (N-cap) and Asp27 residues. Although electrostatic repulsion was observed between Asp18 and Asp27 residues in 18D/27D lysozyme, the dissociation of each residue contributed to stabilizing the B-helix in 18D/27D lysozyme through hydrogen bonding and charge-helix macrodipole interaction. This is the first evidence that two neighboring negative charges at the N-terminus of the helix both increased the stability of the protein.

Amino Acid Sequence↗
PubMed1997

Analysis of the stability of mutant lysozymes at position 15 using X-ray crystallography.

His 15 of hen lysozyme is located at the protein surface and is partly buried by the neighboring residues. The side chain of His 15 forms hydrogen bonds with surrounding residues and these hydrogen bonds are somewhat buried. A series of mutant lysozymes at the position 15 (Gly, Ala, Val, and Phe) was prepared, and their stabilities were analyzed by GdnHCl denaturation and X-ray crystallography. The mutants were less stable than the wild type at pH 5.5 and 35 degrees C. In H15G and H15A, X-ray crystallography revealed two fixed water molecules at the mutated region, which formed similar hydrogen bonds to those in the wild type. On the other hand, it was suggested that the hydrogen bonds were disrupted and that several unfavorable van der Waals' contacts occurred in H15V and H15F. Therefore, we concluded that His 15 stabilized the lysozyme structure by forming hydrogen bonds and the best packing with the neighboring residues. Moreover, we found that the method of protein stabilization by increasing the hydrophobicity of an amino acid residue was not always effectively applicable, especially when the residue had formed a hydrogen bond.

Animals↗
PubMedDate not supplied

Analysis of antibiotic stability in a parenteral nutrition solution.

In children receiving multiple antibiotics and total parenteral nutrition (TPN), the amount of nutrition received can be less than optimal if the central venous line is used for administration of blood products, antibiotics and other medications. The purpose of this study was to evaluate the compatibility of commonly used antibiotics in our standard hyperalimentation solution to determine whether these drugs could be administered in a "piggyback" fashion with parenteral nutrition. If there were no incompatibility this could allow significantly more TPN to be delivered without need for extra fluid in patients receiving antibiotics several times daily. We found 13 antibiotics (amikacin, azlocillin, cefamandole, cephalothin, gentamicin, mezlocillin, moxalactam, nafcillin, oxacillin, penicillin, piperacillin, ticarcillin and tobramycin) to be stable for 6 hours and compatible with the TPN solution. They could be safely given in the presence of the hyperalimentation preparation (1.5% amino acid, 15% dextrose, vitamins, calcium (300 mg/liter) and standard electrolyte concentrations).

Anti-Bacterial Agents↗
PubMed1994

Biomechanical analysis of cervical stabilization systems. An assessment of transpedicular screw fixation in the cervical spine.

STUDY DESIGN: The biomechanical stability of seven cervical reconstruction methods including the transpedicular screw fixation was evaluated under four instability patterns. These four modalities, based on the range and grade of instability, allowed a reproducible biomechanical assessment to establish the in vitro role of internal fixation in the cervical spine. OBJECTIVES: This study biomechanically investigated the stability of seven reconstruction methods in the cervical spine as influenced by four instability patterns and assessed whether three-column fixation for the cervical spine using transpedicular screw fixation would provide increased stability over that of conventional cervical fixation systems. METHODS: A total of 24 calf cervical spine specimens were divided into four experimental groups. The spinal constructs including seven reconstruction techniques--the posterior AO titanium reconstruction plate, Bohlman's posterior triple-wiring, transpedicular screw fixation, anterior iliac bone graft, anterior AcroMed plate, anterior AO titanium locking plate, and combined fixation with the AO anterior plate and posterior triple-wiring--were tested under four loading modes. RESULTS: Anterior plating methods provided less stability than that of posterior constructs under axial, torsional, and flexural loading conditions. Exclusive posterior procedures provided increased stability compared with the intact spine in one level fixation, however, did not sustain the torsional stability when the anterior and middle column was eliminated in two-level fixation. The stabilizing capabilities of both the combined fixation and transpedicular screw fixation were clearly demonstrated in all loading modes, however, those of the latter were superior in multilevel fixation. CONCLUSION: Front and back approaches, employing the anterior plate and posterior triple-wiring, and transpedicular screw fixation demonstrated clear biomechanical advantages when the extent of instability increased to three-column or multilevel. Three-column fixation for the cervical spine using transpedicular screw fixation offers increased stability over that of conventional cervical fixation systems, particularly in multiple level constructs.

Animals↗
PubMed2005

Biomechanical analysis of rigid stabilization techniques for three-column injury in the lower cervical spine.

STUDY DESIGN: Comparison of nondestructive multidirectional flexibility in groups of specimens receiving two different posterior instrumentation constructs with or without anterior plating. OBJECTIVE: To compare stability after a three-column injury stabilized posteriorly by lateral mass screws-rods at C5-C6 and pedicle screws-rods at C7 ("LLP") or by pedicle screws-rods at C5-C6-C7 ("PPP"), and to compare posterior, anterior, and combined anterior-posterior fixation. SUMMARY OF BACKGROUND DATA: Pedicle screws resist pullout better than lateral mass screws, but little research has compared the stability of pedicle screws to that of lateral mass screws used within constructs. METHODS: Fourteen human cadaveric C4-T1 specimens were tested intact, posteriorly instrumented (7 LLP and 7 PPP), anteriorly instrumented, or with combined (anterior-posterior) instrumentation. Nonconstraining, nondestructive torques induced flexion, extension, lateral bending, and axial rotation while angular motion was recorded optically. RESULTS: Posterior, anterior, and combined instrumentation each significantly improved stability (P < 0.05). Combined fixation provided significantly better stability than either anterior or posterior instrumentation alone. In no loading mode and in no testing condition was any parameter significantly different between LLP and PPP. Posterior instrumentation provided significantly better stability than anterior instrumentation. CONCLUSIONS: Anterior plate and posterior screw-rod fixation alone improve stability in a two-level, three-column cervical injury model. Combined fixation further improves stability. There is little discernible difference in immediate postoperative stability between posterior rod constructs combining lateral mass and pedicle screws and those using only pedicle screws.

Adult↗
PubMed2004

First principles analysis of the stability and diffusion of oxygen vacancies in metal oxides.

Oxygen vacancies in metal oxides are known to determine their chemistry and physics. The properties of neutral oxygen vacancies in metal oxides of increasing complexity (MgO, CaO, alpha-Al2O3, and ZnO) have been studied using density functional theory. Vacancy formation energies, vacancy-vacancy interaction, and the barriers for vacancy migration are determined and rationalized in terms of the ionicity, the Madelung potential, and lattice relaxation. It is found that the Madelung potential controls the oxygen vacancy properties of highly ionic oxides whereas a more complex picture arises for covalent ZnO.

Journal Article↗
PubMed1993

Further studies of 31 temperature-sensitive mutants of mouse cytomegalovirus: thermal stability, replication and analysis of temperature-sensitive functions by temperature shift.

A study of 31 temperature-sensitive mutants of mouse cytomegalovirus has indicated that two mutants (tsm1, tsm31) may be defective in immediate-early/early functions, two (tsm2, tsm3) may be defective in early functions and six (tsm9, tsm18, tsm22, tsm23, tsm28, tsm30) may be defective in early/late functions while the remainder are late function-defective mutants as determined by temperature-shift experiments. Three mutants (tsm1, tsm2, tsm3) were more thermostable than wild-type virus while three (tsm16, tsm26, tsm28) were more thermolabile; the remainder were similar in their thermostability to wild-type virus.

Muromegalovirus↗
PubMed2005

Real-time quantitative reverse transcription-PCR analysis of expression stability of Actinobacillus pleuropneumoniae housekeeping genes during in vitro growth under iron-depleted conditions.

The aims of the present investigation were to develop and test a sensitive and reproducible method for the study of gene expression in the porcine lung pathogen Actinobacillus pleuropneumoniae by real-time quantitative reverse transcription (RT)-PCR and to evaluate a number of suitable internal controls, as such controls have not been defined yet for this bacterium. Bacterial gene expression was studied during in vitro exponential and early stationary growth in medium with and without sufficient iron, respectively. First, the stability of expression of five genes, the glyA, tpiA, pykA, recF, and rhoAP genes involved in basic housekeeping, was evaluated on the basis of the mean pairwise variation. All the housekeeping genes included were stably expressed under the conditions investigated and consequently were included in the normalization procedure. Next, the geometric mean of the internal control genes was used to correct five genes of interest. These genes were three genes involved in iron acquisition (tbpA, exbB, and fhuD), the heat shock protein gene groEL, and a putative quorum-sensing gene (luxS). The level of tbpA, exbB, and fhuD expression in A. pleuropneumoniae showed significant up-regulation under iron-restricted conditions compared to bacteria grown in medium with sufficient iron. The observed expression patterns of the genes of interest were consistent with previous observations. This study therefore lends further support to the use of real-time quantitative RT-PCR, with the glyA, tpiA, pykA, recF, and rhoAP genes as internal controls, for future similar gene expression studies in A. pleuropneumoniae.

Actinobacillus pleuropneumoniae↗
PubMed1999

Analysis of the stabilizing effect of Rom on the genetic network controlling ColE1 plasmid replication.

A stochastic model of ColE1 plasmid replication is presented. It is implemented by using UltraSAN, a simulation tool based on an extension of stochastic Petri nets (SPNs). It allows an exploration of the variation in plasmid number per bacterium, which is not possible using a deterministic model. In particular, the rate at which plasmid-free bacteria arise during bacterial division is explored in some detail since spontaneous plasmid loss is a widely observed empirical phenomenon. The rate of spontaneous plasmid loss provides an evolutionary explanation for the maintainance of Rom protein. The presence of Rom acts to reduce variance in plasmid copy number, thereby reducing the rate of plasmid loss at bacterial division. The ability of stochastic models to link biochemical function with evolutionary considerations is discussed.

Cell Division↗
PubMed1993

Structural and genetic analysis of protein stability.

One very encouraging development has been the freedom with which amino acid replacements can be introduced in a protein of interest. This has made it possible to obtain detailed structural and thermodynamic data on a wide variety of mutants that modify protein stability. Substitutions of solvent-exposed amino acids on the surfaces of proteins are seen to have little if any effect on protein stability or structure, leading to the view that it is the rigid parts of proteins that are critical for folding and stability. There is every reason to expect that it will be possible to rationalize the stabilities of mutant proteins from accurate knowledge of their structures. Substantial progress is being made in quantitating the interactions that determine and stabilize protein structures. Although not specifically the subject of this review, substantial progress is also being made in developing methods to engineer proteins of enhanced stability.

Drug Stability↗
PubMed1989

Genetic analysis of protein stability and function.

There is tremendous variability in the importance of individual amino acids in protein sequences. On the one hand, nonconservative residue substitutions can be tolerated with no loss of activity at many residue positions, especially those exposed on the protein surface. On the other hand, destabilizing mutations can occur at a large number of different sites in a protein, and for many proteins such mutations account for more than half of the randomly isolated missense mutations that confer a defective phenotype. At sites that are key determinants of stability or activity, even residue substitutions that are generally considered to be conservative (e.g., Glu in equilibrium Asp, Asn in equilibrium Asp, Ile in equilibrium Leu, Lys in equilibrium Arg and Ala in equilibrium Gly) can have severe phenotypic effects. Unfortunately, this means that there is no simple way to infer the likely effect of an amino acid substitution on the basis of sequence information alone. A nonconservative Gly----Arg substitution could be phenotypically silent at one position while a conservative Asn----Asp change could lead to complete loss of activity at another position. For proteins whose structures are known, it is often possible to predict whether particular residue substitutions will be destabilizing, as long as detailed estimates of the destabilization energy are not required. Substitutions that introduce polar groups, large cavities, or overly large side chains into the hydrophobic core are potentially the most destabilizing. Substitutions that disrupt hydrogen bonding or electrostatic interactions can also have significant effects, although the destabilization caused by these substitutions is smaller than that caused by severe core mutations. Destabilizing substitutions that involve replacing glycines in turns, or introducing prolines into alpha-helices and other disallowed positions are also reasonably common. Finally, most solvent exposed residues can apparently be freely substituted without serious effects on protein stability. Although exceptions may occur, these generalizations serve to summarize a large body of information and can be rationalized in physical and chemical terms. It is an especially encouraging result that proteins appear to tolerate most substitutions, even those that are destabilizing, without significant changes in the native structure. For proteins whose structures are known, this means that it is reasonable to interpret mutant phenotypes in terms of the wild-type structure. For proteins whose structures are not known, it is reasonable to infer that mutations that reduce activity without affecting stability are directly involved in function.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1987

Osteochondritis dissecans: analysis of mechanical stability with radiography, scintigraphy, and MR imaging.

Twenty-one joints with stable (n = 9) or loose (n = 12) osteochondritis dissecans (OCD) lesions were examined in 15 subjects with plain radiography, three-phase bone scintigraphy, and magnetic resonance (MR) imaging. The lesion size and the thickness of the sclerotic margin as measured on plain radiographs were good parameters for predicting loosening. However, bone scintigraphy was more sensitive and specific in determining the mechanical stability of OCD lesions. MR imaging permitted direct visualization of loosening and fragment displacement; the latter permits differentiation of in situ loosening from a grossly unstable lesion. The noninvasive nature of bone scintigraphy and MR imaging makes them potentially preferable diagnostic modalities to arthrography for evaluating the mechanical status of OCD lesions.

Adolescent↗
PubMedDate not supplied

Ankle sprain prophylaxis: an analysis of the stabilizing effects of braces and tape.

Five cadaveric ankles were used to determine the effects of prophylactic bracing and tape on resisting an inversion moment applied to the ankle. The ankles were tested in neutral flexion and 30 degrees of plantar flexion and with both low- and high-top shoes. Eight different strap-on braces were studied. High-top sneakers significantly increased the passive resistance to inversion afforded by all braces and tape. Many of the braces functioned to resist inversion at a level that was comparable with or exceeded the capability of freshly applied tape. This finding was independent of the type of footwear. Braces that were not as effective as freshly applied tape nevertheless retained the advantage over tape in that they could be easily readjusted and their effectiveness restored, whereas the quality of the support provided with tape deteriorated with usage.

Adult↗
PubMed2003

Spectroscopic analysis of the stability of bothrops myotoxic phospholipases A2 to guanidine and urea denaturation.

Spectrophotometric profiles representing the unfolding induced by guanidine on Bothrops moojeni myotoxins-I (MjTX-I) and II (MjTX-II), Bothrops jararacussu bothropstoxin-I (BthTX-I) and Bothrops pirajai piratoxin-I (PrTX-I) were obtained and compared with those obtained with bovine ribonuclease A (RNAse) and trypsin. The molar (epsilon(1M)) and percent (epsilon(1%)) extinction coefficients were determined for the four myotoxins as well as for RNAse and trypsin as reference parameters. These coefficients were then used throughout this work. The changes in free energy (deltaGD(H)(2)(O)) corresponding to zero guanidine concentration and the guanidine concentrations (D(1/2)) able to convert 50% of the molecules from the native to the unfolded state were determined. The values of deltaGD (H)(2)(O) ranged from 4.42 (BthTX-I) to 8.02 (MjTX-I) kcal/mole, compared with 6.47 and 6.88 kcal/mole for trypsin and RNAse, respectively. The values for deltaGD(H)(2)(O) and D1/2 showed that BthTX-I is the least stable among the four myotoxins assayed, with a D1/2 close to that of RNAse, while MjTX-II is conformationally the most stable. Monitoring of the unfolding of RNAse and PrTX-I by a 0 to 6 M urea gradient PAGE revealed transitions from the native (N) to the unfolded (U) state with deltaG(N-U)of 0.22 and 0.41 kcal/mole, respectively. Sigmoidal curves showed well-defined two-stage transitions for both proteins.

Animals↗