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PubMedDate not supplied

The effect of pH and oxygen concentration on the formation of 3-ketodisaccharides by Agrobacterium tumefaciens.

The further optimization of 3-ketodisaccharide formation with sucrose, leucrose and iso maltulose was studied with special regard to pH and oxygen concentration in the reaction mixture with resting cells of Agrobacterium tumefaciens. It was found that the optimal pH values for the highest reaction rate and highest yield were different as the pH affected the stability of the 3-keto derivatives formed. A pH shift to 5.0 clearly reduced the enzymatic degradation of the 3-keto derivatives thus stabilizing them. The influence of constant oxygen concentrations on 3-ketosucrose formation was tested showing results not explicable with normal Michaelis-Menten kinetics. For each substrate a maximum of reaction rate and yield were obtained at very low oxygen concentrations.

Agrobacterium tumefaciens↗
PubMed1997

Preparation and stabilization of heparin/gelatin complex coacervate microcapsules.

The aims of this study are to optimize conditions for the preparation, stabilization, and harvesting of heparin/gelatin microcapsules prepared by complex coacervation. Microelectrophoresis and dry coacervate weight were used to determine the optimum conditions of pH and ionic strength for maximum heparin/gelatin coacervate yield. Heparin/gelatin microcapsules were formed by complex coacervation in the presence and absence of poly(1-vinyl-2-pyrrolidone) (PVP), which was used as a stabilizer. The microcapsules were collected using a spray-drying technique. Microcapsule particle size was analyzed using an AccuSizer optical sizer. Optimized conditions for maximum coacervate yield were pH 2.6, ionic strength 10 mM, and a 1:2 heparin/gelatin A ratio. PVP stabilized the heparin/gelatin coacervate droplets and reduced droplet aggregation during spray-drying. The mean particle diameter of the spray-dried coacervate droplets was lower in the presence of PVP and was unaffected by PVP concentration (in the range 0.5-2.0% w/w). Heparin/gelatin microcapsules, prepared under conditions optimized for maximum coacervate yield, were stabilized without the use of chemical cross-linking agents. Stabilization was achieved by a combination of the addition of PVP and spray-drying.

Drug Carriers↗
PubMed2005

Interactions between nanoparticles in supercritical fluids: from repulsion to attraction.

We present a density functional theory study of interactions between sterically stabilized spherical nanoparticles in a supercritical solvent. The theory is used to analyze the effect of particle size, solvent density, and solvent-ligand interaction strength on the potential of mean force between the particles. Experimentally observed size-selective precipitation of nanoparticles is rationalized in terms of the behavior of the density profiles of stabilizing ligands as a function of particle size and solvent thermodynamic conditions. The theory yields the same general trends as observed in experiments, namely, an increased stability of nanoparticle dispersions at higher solvent densities and for smaller particle sizes.

Journal Article↗
PubMed2006

Tryptophan 243 affects interprotein contacts, cofactor binding and stability in D-amino acid oxidase from Rhodotorula gracilis.

The flavoenzyme d-amino acid oxidase from Rhodotorula gracilis is a homodimeric protein whose dimeric state has been proposed to occur as a result of (a) the electrostatic interactions between positively charged residues of the betaF5-betaF6 loop of one monomer and negatively charged residues belonging to the alpha-helices I3' and I3'' of the other monomer, and (b) the interaction of residues (e.g. Trp243) belonging to the two monomers at the mixed interface region. The role of Trp243 was investigated by substituting it with either tyrosine or isoleucine: both substitutions were nondisruptive, as confirmed by the absence of significant changes in catalytic activity, but altered the tertiary structure (yielding a looser conformation) and decreased the stability towards temperature and denaturants. The change in conformation interferes both with the interaction of the coenzyme to the apoprotein moiety (although the kinetics of the apoprotein-FAD complex reconstitution process are similar between wild-type and mutant D-amino acid oxidases) and with the interaction between monomers. Our results indicate that, in the folded holoenzyme, Trp243 is situated at a position optimal for increasing the interactions between monomers by maximizing van der Waals interactions and by efficiently excluding solvent.

D-Amino-Acid Oxidase↗
PubMed1990

Stabilization of prostaglandin synthetase by immobilization of goat seminal microsomes on silica gel-G.

Prostaglandin synthetase was immobilized by adsorption of goat vesicular microsomes on silica gel containing CaSO4 (silica gel G). Repeated cycles of enzymatic conversion of arachidonic acid to prostaglandin by the immobilized microsomes increased the product yield by 1.5 fold, in comparison to the same by free microsomal particles. The presence of Ca2+ in silica gel is responsible for this improved yield of prostaglandin as the divalent metal ion stabilized prostaglandin synthetase activity in a remarkable way. Microsomal particles immobilized on solid supports like alumina G and controlled pore glass were not very effective.

Animals↗
PubMed1987

Production of monoclonal antibodies. The effect of hybridoma concentration on the yield of antibody-producing clones.

The relationship between the number of hybrid clones in each well of the primary culture, the yield of antibody-producing wells and the short-term stability of the polyclonal cultures was tested. The results of the study demonstrate that a higher yield of antibody-secreting clones was obtained by employing lower density of hybrids and that instability of antibody secretion by polyclonal cultures is not the result of overgrowth of non-secreting clones.

Animals↗
PubMed2003

High-throughput, genome-scale protein production method based on the wheat germ cell-free expression system.

Cell-free protein synthesis systems can synthesize proteins with high speed and accuracy, but produce only a low yield because of their instability over time. Here we review our recent advances in a cell-free protein synthesis system prepared from wheat embryos. We first addressed and resolved the source of the instability of existing systems in light of endogenous ribosome-inactivating proteins. We found that conventional wheat germ extracts contained the RNA N-glycosidase tritin and other inhibitors such as thionin, ribonucleases, deoxyribonucleases, and proteases that originate from the endosperm and inhibit translation. Extensive washing of wheat embryos to eliminate endosperm contaminants has resulted in extracts with a high degree of stability and activity. To maximize the translation yield and throughput of the system, we then focused on developing the following issues: optimization of the ORF flanking regions, a new strategy to construct PCR-generated DNAs for screening, and design of an expression vector for large-scale protein production. The resulting system achieves high-throughput expression, with a PCR-directed system at least 50 genes that can be translated in parallel, yielding between 0.1 and 2.3 mg of protein by one person within 2 days. Under the dialysis mode of reaction, the system with the expression vector can maintain productive translation for 14 days. The cell-free system described here bypasses most of the biological processes and lends itself to robotic automation for high-throughput expression of genetic information, thus opening up many possibilities in the post-genome era.

Cell-Free System↗
PubMed2002

The Essex-Lopresti fracture-dislocation factors in early management and salvage alternatives.

Treatment recommendations for the Essex-Lopresti lesion have not come very far in 50 years. Although there have been multiple biomechanical studies, the biomechanics of forearm loading and stability remain somewhat elusive. Clinical studies have yielded some insight, but predictable outcomes are exceptional. More studies are needed to further understand the biomechanics of the forearm and provide a basis for reconstruction of the IOL. Although current clinical studies regarding IOL reconstruction and radial head replacement seem promising, long-term results with substantial patient numbers are needed. In the short term, the Essex-Lopresti lesion continues to challenge clinicians.

Biomechanical Phenomena↗
PubMed2003

Synthesis of 4-(1-alkenyl)isoquinolines by palladium(II)-catalyzed cyclization/olefination.

A variety of 4-(1-alkenyl)-3-arylisoquinolines have been prepared in moderate to excellent yields by the Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes. The introduction of an o-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Ketone-containing isoquinolines 36 and 49-51 have also been prepared by this process when unsaturated alcohols are employed as the alkenes.

Journal Article↗
PubMed2004

Everolimus therapeutic concentration range defined from a prospective trial with reduced-exposure cyclosporine in de novo kidney transplantation.

Prospective therapeutic drug monitoring of everolimus was performed in a 1-year multicenter trial in 237 de novo kidney transplant patients. Trough blood levels, rejection episodes, and safety parameters were evaluated to define an appropriate therapeutic concentration range for everolimus in this setting. Patients were randomized to everolimus starting doses of 0.75 mg bid (n = 112) or 1.5 mg bid (n = 125). Doses were then individualized based on everolimus trough blood levels (C0) in an attempt to maintain troughs > or = 3 ng/mL; no upper limit was specified. The regimen also contained corticosteroids and cyclosporine with an early dose reduction in months 2-3 posttransplant based on concentrations 2 hours postdose (C2). Cyclosporine C0 levels were also collected. Prospective therapeutic drug monitoring of everolimus C0 in patients starting at 0.75 mg bid led to dose adjustments in 52% of patients to an average long-term dose of 0.93 +/- 0.36 mg bid. This gave median (10th to 90th percentile) C0 levels of 5.3 (3.4-7.9) ng/mL. In patients starting at 1.5 mg bid, 55% had dose adjustments leading to an average long-term dose of 1.24 +/- 0.35 mg bid. This yielded C0 levels of 7.2 (4.4-11.6) ng/mL. Cyclosporine dosing began on average at 274 +/- 78 mg bid, was down-titrated in months 2-3 from 181 +/- 80 mg to 81 +/- 33 mg bid, and stabilized at 70 +/- 26 mg bid thereafter. This yielded median C2 levels of 1165 ng/mL in month 1, a down-titration with levels of 853 and 630 ng/mL in months 2 and 3, and a posttitration level of 472 ng/mL. The corresponding median cyclosporine C0 was 242 ng/mL initially and 70 ng/mL in the posttitration phase. In patients starting at 0.75 mg bid everolimus and an early down-titration of cyclosporine, everolimus C0 between 3 and 8 ng/mL was an effective and safe concentration range. Concentrations up to 12 ng/mL were tolerated over the first year posttransplant. This trial demonstrated that therapeutic monitoring of everolimus can be prospectively performed for dose individualization. Maintaining everolimus troughs in the range 3 to 8 ng/mL in the first posttransplant year with reduced-exposure cyclosporine is associated with good efficacy and safety profiles.

Adrenal Cortex Hormones↗
PubMed2001

Uniaxial compression measurement device for investigation of the mechanical stability of biofilms.

The mechanical stability of biofilms is important for biotechnology, as sloughing of the biomass due to mechanical failure of the biofilm matrix can lead to severe interferences with biofilm processes. In cases of biofouling, biofilms have to be removed, in which case their mechanical stability must be overcome. The apparent modulus of elasticity and the yield strength as obtained from uniaxial compression experiments can be taken as parameters indicative for the mechanical stability of a biofilm. A film rheometer is presented which allows for the determination of these quantities, using model biofilms of Pseudomonas aeruginosa grown on membrane filters. The compressive stress-strain behaviour up to the point of failure is recorded at a compression speed of 1 microm s(-1). In accordance with the stress-strain curve, the investigated biofilm can be described as viscoelastic material, which demonstrates plastic flow properties. The extracellular polymeric substances (EPS), which keep biofilms together, form a temporary network of fluctuating junction points. Above the yield point, the gel structure fails and the system behaves as a highly viscous fluid. The apparent modulus of elasticity and the yield point are considered to be useful parameters for characterizing the mechanical properties of biofilms.

Biofilms↗
PubMed2001

Ca(2+) stabilizes the semiquinone radical of pyrroloquinoline quinone.

Spectroelectrochemical studies were performed on the interaction between Ca(2+) and pyrroloquinoline quinone (PQQ) in soluble glucose dehydrogenase (sGDH) and in the free state by applying a mediated continuous-flow column electrolytic spectroelectrochemical technique. The enzyme forms used were holo-sGDH (the holo-form of sGDH from Acinetobacter calcoaceticus) and an incompletely reconstituted form of this, holo-X, in which the PQQ-activating Ca(2+) is lacking. The spectroelectrochemical and ESR data clearly demonstrated the generation of the semiquinone radical of PQQ in holo-sGDH and in the free state in the presence of Ca(2+). In contrast, in the absence of Ca(2+) no semiquinone was observed, either for PQQ in the free state (at pH 7.0) or in the enzyme (holo-X). Incorporation of Ca(2+) into the active site of holo-X, yielding holo-sGDH, caused not only stabilization of the semiquinone form of PQQ but also a negative shift (of 26.5 mV) of the two-electron redox potential, indicating that the effect of Ca(2+) is stronger on the oxidized than on the reduced PQQ. Combining these data with the observations on the kinetic and chemical mechanisms, it was concluded that the strong stimulating effect of Ca(2+) on the activity of sGDH can be attributed to facilitation of certain kinetic steps, and not to improvement of the thermodynamics of substrate oxidation. The consequences of this conclusion are discussed for the oxidative as well as for the reductive part of the reaction of sGDH.

Acinetobacter calcoaceticus↗
PubMed2002

Expression and characterization of recombinant murine factor VIII.

Hemophilia A is the inherited bleeding disorder that results from mutation of blood coagulation factor VIII (fVIII). Described here is the generation of a regulated expression system producing recombinant murine fVIII. Murine B-domainless fVIII was expressed at a peak level of 4 units/106 cells/24 h in serum-free media. Subsequently, a two-step purification procedure resulted in 5,300-fold enrichment and a 70% yield. Highly purified recombinant murine fVIII had a specific coagulant activity of 660 units per nanomole. It underwent proteolytic processing by thrombin to yield an activated heterotrimer that demonstrated significantly greater stability than activated human fVIII. Recombinant murine fVIII was utilized to generate an anti-fVIII polyclonal antibody. Intravenous injection of recombinant murine fVIII into hemophilia A mice failed to induce a significant anti-fVIII immune response using a schedule that yielded high titer inhibitory antibodies to human fVIII. This may provide an important model for the study of immune tolerance to fVIII.

Animals↗
PubMed1997

N-Nmoc-L-glutamate, a new caged glutamate with high chemical stability and low pre-photolysis activity.

We report the synthesis, the physicochemical characterization, and biological evaluation of a new caged glutamate, N-(o-nitromandelyl)oxycarbonyl-L-glutamic acid (Nmoc-Glu), that liberates free glutamate on photolysis. The low affinity of certain glutamate receptors and their rapid entry into desensitization have effectively prevented the creation of an ideal caged glutamate. In the absence of an ideal compound, Nmoc-Glu was designed to resist spontaneous hydrolysis while maintaining reasonable photorelease yield and kinetics. Chemical and physiological analyses reveal that Nmoc-Glu, indeed, has exceptionally low residual activity and high chemical stability. The quantum yield of Nmoc-Glu is 0.11. Photolytic uncaging and release of free glutamate occur in two steps, consisting of an initial light-induced cleavage that proceeds on the sub-millisecond time scale, and a subsequent light-independent, pH-dependent decarboxylation step that proceeds on the millisecond time scale. The low residual activity and high chemical stability of Nmoc-Glu are important advantages in applications where pre-photolysis Glu receptor activation and desensitization must be minimized.

Animals↗
PubMed2001

Allophycocyanin 1 as a near-infrared fluorescent tracer: isolation, characterization, chemical modification, and use in a homogeneous fluorescence resonance energy transfer system.

Allophycocyanin 1 (APC1), isolated from Mastigocladus laminosus, retains the same (alpha-beta)(3) trimeric structure as allophycocyanin (APC), but incorporates a peptide linker in its core leading to a 28% increase in its fluorescence quantum yield compared to APC. Moreover, APC1 exhibits an unexpectedly good stability at very low concentrations, at extreme pHs, or diluted in a low ionic strength medium whereas, under the same conditions, APC dissociates into an (alpha-beta) monomer, indicating that the peptide linker acts as a stabilizer of its trimeric structure. APC1 crosslinking experiments performed using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide gave a high reaction yield (95%) and showed a similar crosslinking process as previously described for APC. Fluorescence quantum yields of crosslinked APC1 or APC decrease by 20% after labeling on antibody or streptavidin. However, quantum yields of the crosslinked APC1 conjugates remain 25% higher than those of crosslinked APC conjugates. Associated with a europium trisbipyridine cryptate as donor, crosslinked APC1 was compared with crosslinked APC as acceptor in homogeneous time resolved fluorescence technology based on a fluorescence resonance energy transfer process. Using crosslinked APC1, assay performances were increased by 20%, showing that APC1 could be considered as a very promising near infrared fluorescent probe to replace APC in its biological applications.

Chromatography, Gel↗
PubMed1999

A quantitative method for evaluating the stabilities of nucleic acids.

We report a general method for screening, in solution, the impact of deviations from canonical Watson-Crick composition on the thermodynamic stability of nucleic acid duplexes. We demonstrate how fluorescence resonance energy transfer (FRET) can be used to detect directly free energy differences between an initially formed "reference" duplex (usually a Watson-Crick duplex) and a related "test" duplex containing a lesion/alteration of interest (e.g., a mismatch, a modified, a deleted, or a bulged base, etc.). In one application, one titrates into a solution containing a fluorescently labeled, FRET-active, reference duplex, an unlabeled, single-stranded nucleic acid (test strand), which may or may not compete successfully to form a new duplex. When a new duplex forms by strand displacement, it will not exhibit FRET. The resultant titration curve (normalized fluorescence intensity vs. logarithm of test strand concentration) yields a value for the difference in stability (free energy) between the newly formed, test strand-containing duplex and the initial reference duplex. The use of competitive equilibria in this assay allows the measurement of equilibrium association constants that far exceed the magnitudes accessible by conventional titrimetric techniques. Additionally, because of the sensitivity of fluorescence, the method requires several orders of magnitude less material than most other solution methods. We discuss the advantages of this method for detecting and characterizing any modification that alters duplex stability, including, but not limited to, mutagenic lesions. We underscore the wide range of accessible free energy values that can be defined by this method, the applicability of the method in probing for a myriad of nucleic acid variations, such as single nucleotide polymorphisms, and the potential of the method for high throughput screening.

Base Sequence↗
PubMed2003

Fabrication of homogeneously cross-linked, functional alginate microcapsules validated by NMR-, CLSM- and AFM-imaging.

Cross-linked alginate microcapsules of sufficient mechanical strength can immunoisolate cells for the long-term treatment of hormone and other deficiency diseases in human beings. However, gelation of alginate by external Ba(2+) (or other divalent cations) produces non-homogeneous cross-linking of the polymeric mannuronic (M) and guluronic (G) acid chains. The stability of such microcapsules is rather limited. Here, we show that homogeneous cross-linking can be achieved by injecting BaCl(2) crystals into alginate droplets before they come into contact with external BaCl(2). The high effectiveness of this crystal gun method is demonstrated by confocal laser scanning microscopy and by advanced nuclear magnetic resonance imaging. Both techniques gave clear-cut evidence that homogeneous cross-linkage throughout the microcapsule is only obtained with simultaneous internal and external gelation. Atomic force microscopy showed a very smooth surface topography for microcapsules made by the crystal gun method, provided that excess Ba(2+) ions were removed immediately after gelation. In vitro experiments showed greatly suppressed swelling for crystal gun microcapsules. Even alginate extracted from Lessonia nigrescens (highly biocompatible) yielded microcapsules with long-term mechanical stability not hitherto possible. Encapsulation of rat islets, human monoclonal antibodies secreting hybridoma cells and murine mesenchymal stem cells transfected with cDNA encoding for bone morphogenetic protein (BMP-4) revealed that injection of BaCl(2) crystals has no adverse side effects on cell viability and function. However, the release of low-molecular weight factors (such as insulin) may be delayed when using alginate concentrations in the usual range.

Alginates↗
PubMed1999

The chimeric peptide [Lys(-2)-Arg(-1)]-sarafotoxin-S6b, composed of the endothelin pro-sequence and sarafotoxin, retains the salt-bridge staple between Arg(-1) and Asp8 previously observed in [Lys(-2)-Arg(-1)]-endothelin. Implications of this salt-bridge in the contractile activity and the oxidative folding reaction.

The chimeric peptide [Lys(-2)-Arg(-1)]-sarafotoxin-S6b (KR-SRTb) designed from the Lys-2-Arg-1 dipeptide of the endothelin pro-sequence and the sarafotoxin-S6b sequence was synthesized. Its contractile activity was found to be decreased markedly when compared with that of the parent SRTb. In contrast, the extension by the Lys-Arg dipeptide was found to increase the formation of the native disulfide isomer (82/18 versus 96/4) when the reaction was carried out in the presence of redox reagents. The solution structure of KR-SRTb was determined by NMR as a function of pH. In the carboxylic acid state, the structure consists of the cystine-stabilized alpha-helical motif, with the alpha-helical part spanning residues 9-15, and of an unstructured C-terminal tail. In the carboxylate state, the structure is characterized by a salt-bridge between Arg(-1) and Asp8, which we identified previously in the [Lys(-2)-Arg(-1)]-endothelin-1 peptide (KR-ET-1). The fact that this salt-bridge is commonly observed in KR-SRTb and KR-ET-1, despite the 33% sequence difference between the corresponding parental peptides, highlights the remarkable adaptability of the Lys-Arg extension for the formation of a special salt-bridge. As a consequence, this salt-bridge, which does not depend on either the 4-7 sequence of the loop or the C-terminal sequence, appears to be particularly well suited to improve the stability of the cystine-stabilized alpha-helical motif. Therefore, because of its high yield in the native disulfide arrangement and its high permissiveness for sequence mutation in the 4-7 loop, such a stabilized cystine-stabilized alpha-helical motif could be a valuable scaffold for the presentation of a library of constrained short peptides.

Amino Acid Sequence↗