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PubMed1994

The attractiveness of the Droop equations. II. Generic uptake and growth functions.

In a recent paper the authors proved global asymptotic stability of the Droop equations. This system of nonlinear ordinary differential equations describes the growth of a microorganism in a chemostat. In this setting the growth rate of the organism is limited by the availability of a single nutrient. The state variables of the Droop system are biomass density, intracellular nutrient concentration. (I"cell quota" in Droop's terminology), and extracellular nutrient concentration. In the current paper the authors relax Droop's particular choices for the uptake and growth functions. Characterizing these functions in qualitative terms only, they again reach the same conclusion of global asymptotic stability. Their analysis relies on reducing the three-dimensional Droop system to a two-dimensional system via the first integral of Burmaster.

Biological Transport, Active↗
PubMed1989

Stability of gels formed following coagulation of Limulus amebocyte lysate: lack of covalent crosslinking of coagulin.

Incubation of lysates prepared from amebocytes of the horseshoe crab (Limulus polyphemus) with bacterial endotoxin results in coagulation and formation of a solid gel. Although Limulus gels remained solid indefinitely, if undisturbed, they were easily disrupted by mechanical agitation. Chemical solubility studies of gelled lysates demonstrated rapid solubilization of gels in monochloroacetic acid, a property of clots that have not been covalently stabilized; but in contrast demonstrated resistance to solubilization by urea, a property of stabilized clots. Analysis of solubilized proteins by polyacrylamide gel electrophoresis in SDS demonstrated coagulin, the designation for the activated form of coagulogen (the clottable protein) that forms a gel, only in samples derived from clotted lysate that had been previously incubated with monochloroacetic acid, but not in samples following incubation with urea, confirming the results of the chemical solubility studies. Enzymatic assays for transpeptidase (Factor XIII-like) activity in either native or gelled Limulus lysates were negative. Furthermore, analysis for covalently crosslinked peptides in gelled coagulin confirmed the absence of intermolecular gamma-glutamyl-epsilon-lysyl bonds. Therefore, the stable gels formed following coagulation of Limulus lysate by bacterial endotoxin are not covalently crosslinked.

Animals↗
PubMed1983

The antitumor complex ethylenediamine platinum (II) malonate: x-ray structure analysis, and studies of its stability in solution.

The anti-tumour compound ethylenediamine platinum (II) malonate has been examined by x-ray crystallography. The molecular structure has a square-planar arrangement around the platinum atom, with the malonate group in a boat conformation and cis to the ethylenediamine group. Solution studies have shown that the malonate ion may be readily displaced from the complex, especially by chloride ion, and at low pH. The implications of this finding for in vivo drug administration are discussed.

Antineoplastic Agents↗
PubMed1987

A computerized analysis of the shape and stability of mandibular arch form.

To determine whether a particular ideal orthodontic arch form could be identified, the mandibular dental casts of 30 untreated normal cases, 30 Class I nonextraction cases, and 30 Class II nonextraction cases were examined. Following computerized digitizing and the use of a mathematic function called polynomial of the fourth degree, arch forms were generated for each sample and then compared to 17 commercially produced arch forms. Results showed that no particular arch form predominated in any of the three samples. A shape representing a combination of the "Par" and "Vari-Simplex" arch forms approximated to only 50% of the cases in the three samples. The remaining 50% of the cases displayed a wide variety of arch forms. Cases that had changes in arch form during nonextraction treatment frequently were not stable; almost 70% showed significant long-term posttreatment changes. Customizing arch forms appears to be necessary in many cases to obtain optimum long-term stability because of the great individual variability in arch form found in this study.

Adolescent↗
PubMed1991

Analysis and modulation of protein stability.

Numerous site-directed mutagenesis experiments have provided new insights into the stabilizing role of the individual forces and interactions within a globular protein molecule. Some useful guidelines and procedures are now available for producing genetically more stable proteins. Examples are the introduction of disulfide bonds, ion-binding sites, salt bridges, hydrophobic residues or hydrogen bonds, and the improvement of hydrophobic packing or alpha-helix propensity. Moreover, it is now clearly recognized that thermophilic (and, in general, extremophilic) bacteria produce highly stable proteins and enzymes of practical interest.

Amino Acid Sequence↗
PubMed2006

Characterization of Saccharomyces cerevisiae Atm1p: functional studies of an ABC7 type transporter.

Saccharomyces cerevisiae Atm1p has been cloned, over-expressed and purified from a yeast expression system. The sequence includes both the soluble ATPase and transmembrane-spanning domains. With the introduction of an N-terminal Kozak sequence and a C-terminal (His)(6)-tag, a yield of 1 mg of Atm1p was obtained from 3 g wet yeast cells, which is comparable to other membrane-associated proteins isolated from eukaryotic expression systems. The ATPase activity of Atm1p is sensitive to sodium vanadate, a P-type ATPase inhibitor, with an IC(50) of 4 microM. MgADP is a product inhibitor for Atm1p with an IC(50) of 0.9 mM. The Michaelis-Menten constants V(max), K(M) and k(cat) of Atm1p were measured as 8.7+/-0.3 microM/min, 107+/-16 microM and 1.24+/-0.06 min(-1), respectively. A plot of ATPase activity versus concentration of Atm1p exhibits a nonlinear relationship, suggesting an allosteric response and an important role for the transmembrane domain in mediating both ATP hydrolysis and MgADP release. The metal dependence of Atm1p ATPase activity demonstrated a reactivity order of Mg(2+)>Mn(2+)>Co(2+), while each divalent ion was found to be inhibitory at higher concentrations. The activation and inhibitory effect of phospholipids suggest that formation of a lipid-micelle complex is important for enzymatic activity and stability. Structural analysis of Atm1p by CD spectroscopy suggested a similarity of secondary structure to that found for other members of this ABC protein family.

ATP-Binding Cassette Transporters↗
PubMed2005

Truncation of the C-terminus of human MLH1 blocks intracellular stabilization of PMS2 and disrupts DNA mismatch repair.

The human DNA mismatch repair (MMR) protein MLH1 has essential roles in the correction of replication errors and the activation of cell cycle checkpoints and cytotoxic responses to DNA damage that contribute to suppression of cancer risk. MLH1 functions as a heterodimer with the PMS2 protein, and steady state levels of PMS2 are very low in MLH1-deficient cells. Unique to MLH1 among MutL-homolog proteins, and conserved in identified eukaryotic MLH1 proteins, is the so-called C-terminal homology domain (CTH). The function of these C-terminal 20-30 amino acids is not known. We investigated the effect of a C-terminal truncation of human MLH1 (MLH1-L749X) on mammalian MMR by testing its activity in MLH1-deficient cells. We found the CTH to be essential for suppression of spontaneous mutation, activation of a cytotoxic response to 6-thioguanine, and maintenance of normal steady state levels of PMS2. Co-expression in doubly mutant Mlh1-/-; Pms2-/- fibroblasts showed that MLH1-L749X was unable to stabilize PMS2. Over-expression of MLH1-L749X did not reduce stabilization of PMS2 mediated by wild-type MLH1, indicating that truncation of the CTH reduces the ability to compete with wild-type MLH1 for interaction with PMS2. Lack of PMS2 stabilization also was observed with a previously reported pathogenic truncation (MLH1-Y750X), but not with two different point mutations in the CTH. Biochemical assays demonstrated that truncation of the CTH reduced the stability of heterodimers, although MLH1-L749X retained significant capacity for interaction with PMS2. Thus, the CTH of human MLH1 is necessary for error correction, checkpoint signaling, and for promoting interaction with, and the stability of, PMS2. Analysis of the CTH role in stabilizing PMS2 was facilitated by a novel intracellular assay for MLH1-PMS2 interaction. This assay should prove useful for identifying additional amino acids in MLH1 and PMS2 necessary for interaction in cells, and for determining the functional consequences of MLH1 mutations identified in human cancers.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Dehydration behavior and structural characterization of the GW275919X monohydrate.

GW275919X, a central muscle relaxant for the treatment of lower back pain, exists in a monohydrate. Knowledge of the solid state dehydration behavior and the crystal structure is essential for determining its relative physical stability. Thermal analysis and hot-stage powder X-ray diffraction were used to study the solid state phase transformation during the dehydration process. Crystal structure was determined by single crystal X-ray analysis. Molecular modeling with Cerius(2) software was used to visualize the hydrate crystal structure and to construct the molecular packing and hydrogen bond diagram. Morphology prediction was performed using the BFDH calculation. Crystallographic data: monoclinic, space group, P21/c, a (Angstrom)=14.3734, b (Angstrom)=5.0336, c (Angstrom)=15.4633 and beta=105.11 degrees. Water molecules in the hydrate crystal of GW275919X are involved in the hydrogen bonds and these hydrogen bonds contribute to the coherence of the crystal structure. The longest dimension of the predicted morphology is in the b-direction, which would correspond to the needle axis of the experimental crystals.

Benzimidazoles↗
PubMed2004

Determination of combined p-hydroxy benzoic acid preservatives in a liquid pharmaceutical formulation by HPLC.

This paper describes a reversed-phase high performance liquid chromatographic (RP-HPLC) assay method for the determination of combined p-hydroxy benzoic acid (ethylparaben (EP), methylparaben (MP) and propylparaben (PP)) preservatives in a liquid pharmaceutical formulation. The chromatographic separation was achieved with potassium phosphate buffer (pH 7.05)-methanol (47.5:52.5, v/v) as mobile phase, a Spherisorb C(18) column (250 mm x 4.6mm) and UV detection at 254 nm. The analysis time was <8 min. The method was validated with respect to linearity, precision, accuracy, selectivity, specificity and ruggedness. The calibration curves showed good linearity over the concentration range of 2-140 microg/ml. The correlation coefficient were >0.9999 in each case. The relative standard deviation (R.S.D.) values for intra- and inter-day precision studies were <1%. The procedure describe here is simple, selective and is suitable for routine quality control analysis and stability tests.

Chemistry, Pharmaceutical↗
PubMed2005

New approach to determination of surface heterogeneity of adsorbents and catalysts from the temperature programmed desorption (TPD) technique: one step beyond the condensation approximation (CA) method.

Recovery of the desorption activation energy distribution from the experimental temperature programmed desorption (TPD) spectra is among the most difficult problems of adsorption science. Since the heterogeneity effects strongly influence on transport, diffusion, and catalytic reaction time, the estimation of their magnitude is very important for practical purposes. Up to the present, several theories have been used for the interpretation of the TPD results. Almost all advanced theoretical approaches take into account the effect of surface disorder (heterogeneity in desorption activation energy); however, they ignore the numerical difficulties coming from the "ill-posed" character of the linear Fredholm integral equations appearing in the theoretical description of the TPD results. Thus, there is a growing interest in developing novel methods supported by powerful numerical algorithms taking this into account. In the current study we propose a new approach and consider the theoretical aspect as well as numerical problems appearing in the TPD analysis. Our modeling is based on the well-known and generally accepted "absolute rate theory," which has been used extensively for the interpretation of TPD results. We propose and verify (applying computer simulations) the new advanced numerical hybrid type algorithms taking into account the heterogeneity effects. They seem to be very promising in TPD spectra analysis. The stability of the proposed advanced numerical methods is confirmed by the computer simulation experiments, and the results are compared with those obtained from the condensation approximation (CA) method.

Journal Article↗
PubMed2005

Simultaneous determination of triamcinolone acetonide and oxymetazoline hydrochloride in nasal spray formulations by HPLC.

A high-performance liquid chromatography (HPLC) method with UV detection at 232 nm was developed and validated for the simultaneous determination of triamcinolone acetonide (TAA) and oxymetazoline hydrochloride (OXY) in nasal spray formulations. The chromatographic system consisted of a micro Bondapak CN column (150 mm x 3.9 mm), 5 microm particle size with a mobile phase composition of acetonitrile:ammonium acetate (pH 5.0, 20mM) (10:90, v/v) at a flow rate of 1.0 mL/min. Calibration curves were linear for both TAA and OXY in the concentration range of 2.5-25.0 microg/mL. The limit of detection and quantitation were 0.29 and 0.88 microg/mL for OXY and 0.24 and 0.73 microg/mL for TAA. The described method was further applied to the analysis and stability studies of two nasal spray formulations I and II prepared from TAA and OXY commercial nasal spray products. The stability of OXY and TAA in the commercial products and the nasal formulations I and II were analyzed after 30 days at room temperature and 30 days at 40 degrees C/60% relative humidity. The results of the stability study showed that OXY and TAA in the commercial nasal spray products and the nasal formulations I and II were stable at 20-25 degrees C (room temperature) but TAA was unstable at 40 degrees C/60% relative humidity. TAA exhibited more than 10% loss at 14 days in both the nasal formulations and in the commercial products. OXY showed increased degradation at 40 degrees C/60% relative humidity but <10%.

Administration, Intranasal↗
PubMed2003

Investigations into the amino-terminal domain of the respiratory syncytial virus nucleocapsid protein reveal elements important for nucleocapsid formation and interaction with the phosphoprotein.

Bacterially expressed nucleocapsid (N) protein, from respiratory syncytial virus (RSV), was used to investigate RNA binding in a modified North-Western blotting protocol. The recombinant protein demonstrated no sequence specificity in binding RNA representing either the antigenomic leader sequence or the nonspecific sequence derived from a plasmid vector. When recombinant N was purified on CsCl gradients, two types of structure, both with densities indicating that they contained RNA, could be visualised by negative-stain electron microscopy. Structures similar to nucleocapsids (NC) from RSV-infected cells were observed, as were ring structures. A small fragment of the N (amino acids 1-92) was all that was required for the production of NC-like structures. Another mutant with an internal deletion could form rings but not NC-like structures. This suggests that this domain (amino acids 121-160) may be important for maintaining helical stability. Further analysis has also identified a potential site in the amino-terminus that may be involved in an interaction with the phosphoprotein. A domain model of the RSV N protein is presented which, similar to that of other paramyxoviruses, supports the idea that the amino-terminus is important for NC assembly.

Animals↗
PubMed2002

Endocytosis: driving membranes around the bend.

When a nascent vesicle buds, the membrane must curve. Several mechanisms have been proposed for curvature creation or stabilization. Structural analysis of the ENTH domain of the endocytic protein epsin has suggested a new mechanism, in which the ENTH domain pushes its way into membranes, thus bending them into shape.

Adaptor Proteins, Vesicular Transport↗
PubMed1997

Human equilibrium on unstable support: the importance of feet-support interaction.

Healthy humans maintained equilibrium on rocking supports (seesaw) of different curvatures and heights. We recorded platform tilt, horizontal displacements of the upper body, ankle joint angle and activity of ankle joint muscles. Subjects maintained balance by making seesaw rotations placing the support under the body's centre-of-gravity. Forward displacement was balanced by compensatory plantariflexion: thus the relation between muscle activity and ankle joint angle differed from that on a rigid floor. Mechanical analysis of stability showed that standing on low seesaws requires ankle torque increase during forward body shift (as on a rigid floor) and torque decrease on high seesaws (when the seesaw height exceeded its radius). In the latter case, balancing was impossible with eyes closed. The results suggest that directionally specific torque changes in response to centre-of-gravity shifts provide important information for maintenance of orthograde posture.

Adult↗
PubMed2003

Optimization of the preparation process for human serum albumin (HSA) nanoparticles.

Nanoparticles prepared by desolvation and subsequent crosslinking of human serum albumin (HSA) represent promising carriers for drug delivery. Particle size is a crucial parameter, in particular for the in vivo behaviour of nanoparticles after intravenous injection. The objective of the present study is the development of a desolvation procedure for the preparation of HSA-based nanoparticles under the aspect of a controllable particle size between 100 and 300 nm in combination with a narrow size distribution. A pump-controlled preparation method was established which enabled particle preparation under defined conditions. Several factors of the preparation process, such as the rate of addition of the desolvating agent, the pH value and the ionic composition of the HSA solution, the protein concentration, and the conditions of particle purification were evaluated. The pH value of the HSA solution prior to the desolvation procedure was identified as the major factor determining particle size. Varying this parameter, (mean) particle diameters could be adjusted between 150 and 280 nm, higher pH values leading to smaller nanoparticles. Washing the particles by differential centrifugation led to significantly narrower size distributions. The reproducibility of the particle size and particle size distribution under the proposed preparation conditions was demonstrated by sedimentation velocity analysis in the analytical ultracentrifuge and the cellular uptake of those nanoparticles was studied by confocal microscope imaging and FACS analysis. The stability of the resulting nanoparticles was evaluated by pH and buffer titration experiments. Only pH values distinctly outside the isoelectric pH range of HSA and low salt concentrations were able to prevent nanoparticle agglomeration.

Drug Delivery Systems↗
PubMed1996

Uncemented total hip arthroplasty using the CLS stem: a titanium alloy implant with a corundum blast finish. Results at a mean 6 years in a prospective study.

An uncemented titanium alloy stem with a corundum blast finish and an uncemented titanium fibermetal mesh socket were implanted in a series of 57 hips. These prostheses were selected for use in the youngest, most active, and/or heaviest candidates for total hip arthroplasty. Fifty hips were available for study at a minimum 60 months. At a mean 6 years, 92% of the hips were rated good or excellent. The mean Harris hip score was 92. One patient experienced mild thigh pain. The corundum blast finish was associated with reliable implant stability. Survival analysis predicted a 96% rate of implant survival at 92 months. Loss of bone density was rated mild, minimal, or none in 88% of the hips. Three hips developed severe bone loss due to systemic disease. Polyethylene wear was measurable in 86% of the hips. Twenty hips developed focal proximal femoral bone erosions. One hip had endosteal cavitation distal to zone 7. The presence of proximal femoral erosions or endosteal cavitation correlated positively with the presence of measurable polyethylene wear. The limited and proximal distribution of femoral bone erosion despite evidence of extensive polyethylene wear suggested that bone apposition to the corundum blast finish resulted in a barrier to migration of wear debris.

Adult↗