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Stabilizing Effects (stabilizing + effects)
Selected AbstractsStabilizing effects of extracellular ATP on synaptic efficacy and plasticity in hippocampal pyramidal neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2005Eduardo D. Martín Abstract The role of adenosine triphosphate (ATP) as a neurotransmitter and extracellular diffusible messenger has recently received considerable attention because of its possible participation in the regulation of synaptic plasticity. However, the possible contribution of extracellular ATP in maintaining and regulating synaptic efficacy during intracellular ATP depletion is understudied. We tested the effects of extracellular ATP on excitatory postsynaptic currents (EPSCs) evoked in CA1 pyramidal neurons by Schaffer collateral stimulation. In the absence of intracellular ATP, EPSC rundown was neutralized when a low concentration of ATP (1 µm) was added to the extracellular solution. Adenosine and ATP analogues did not prevent the EPSC rundown. The P2 antagonists piridoxal-5,-phosphate-azophenyl 2,,4,-disulphonate (PPADS) and reactive blue-2, and the P1 adenosine receptor antagonist 8-cyclopentyltheophylline (CPT) had no detectable effects in cells depleted of ATP. However, the protective action of extracellular ATP on synaptic efficacy was blocked by extracellular application of the protein kinase inhibitors K252b and staurosporine. In contrast, K252b and staurosporine per se did not interfere with synaptic transmission in ATP loaded cells. Without intracellular ATP, bath-applied caffeine induced a transient (< 35 min) EPSC potentiation that was transformed into a persistent long-term potentiation (> 80 min) when 1 µm ATP was added extracellularly. An increased probability of transmitter release paralleled the long-term potentiation induced by caffeine, suggesting that it originated presynaptically. Therefore, we conclude that extracellular ATP may operate to maintain and regulate synaptic efficacy and plasticity in conditions of abnormal intracellular ATP depletion by phosphorylation of a surface protein substrate via activation of ecto-protein kinases. [source] FISCAL DECENTRALIZATION AND THE BUSINESS CYCLE: AN EMPIRICAL STUDY OF SEVEN FEDERATIONSECONOMICS & POLITICS, Issue 1 2010JONATHAN RODDEN Although fiscal policies of central governments sometimes provide modest insurance against regional income shocks, this paper shows that procyclical fiscal policy among provincial governments can easily overwhelm these stabilizing effects. We examine the cyclicality of budget items among provincial governments in seven federations, showing that own-source taxes are generally highly procyclical, and contrary to common wisdom, revenue sharing and discretionary transfers are either acyclical or procyclical. Constituent governments are thus left alone to smooth their own shocks, and we document the extent to which various restraints on borrowing and saving undermine their ability to do so. The resulting procyclicality of provincial fiscal policy is likely to have important implications in a world where demands for countercyclical fiscal policy are increasing but considerable fiscal responsibilities are being devolved to subnational governments. [source] Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational designFEBS JOURNAL, Issue 3 2009Oliver Spadiut The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC 1.1.3.10) catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 °C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association. [source] Localized failure of fibre-reinforced elastic,plastic materials subjected to plane strain loadingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2007Dunja Peri Abstract We consider discontinuous bifurcations as the indicator of a localized failure for a class of composites that are characterized by elastic fibres reinforcing an elastic,plastic matrix. A macroscopic tangent stiffness tensor for the fibre-reinforced composite is developed by consistently homogenizing the contribution of fibres in a spherical representative volume element. Analytical solutions are derived for the critical hardening modulus and corresponding bifurcation directions for the case of plane strain loading. Properties of the solutions are further illustrated on the example of the non-associated Drucker,Prager model at onset of yielding. Results show that presence of fibres decreases the critical hardening modulus, thus inhibiting the onset of strain localization. The rate of decrease in the critical hardening modulus is the highest for pure shear, followed by uniaxial tension, uniaxial compression, biaxial tension and biaxial compression. The main fibre parameters that control the onset of strain localization are their volumetric content and their stiffness modulus whereby very stiff fibres can produce the most significant decrease in the critical hardening modulus, especially for the state of biaxial tension. The critical hardening modulus for the non-associated Drucker,Prager model exhibits a full range of localization modes including compaction bands, dilation bands, and transition in the form of shear bands regardless of the presence of fibres. Presence of fibres affects bifurcation directions, except in the case when Poisson's ratio of the matrix is equal to 0.25. The results demonstrate stabilizing effects of fibres by which they provide the control against the onset of strain localization. Copyright © 2006 John Wiley & Sons, Ltd. [source] Computation of strongly swirling confined flows with cubic eddy-viscosity turbulence modelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2003Xiaodong Yang Graduate Student Abstract An investigation on the predictive performance of four cubic eddy-viscosity turbulence models for two strongly swirling confined flows is presented. Comparisons of the prediction with the experiments show clearly the superiority of cubic models over the linear k,,model. The linear k,,model does not contain any mechanism to describe the stabilizing effects of swirling motion and as a consequence it performs poorly. Cubic models return a lower level of Reynolds stresses and the combined forced-free vortex profiles of tangential velocity close to the measurements in response to the interaction between swirl-induced curvature and stresses. However, a fully developed rotating pipe flow is too simple to contain enough flow physics, so the calibration of cubic terms is still a topic of investigation. It is shown that explicit algebraic stress models require fewer calibrations and contain more flow physics. Copyright © 2003 John Wiley & Sons, Ltd. [source] Role of Rac 1 and cAMP in endothelial barrier stabilization and thrombin-induced barrier breakdownJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2009Y. Baumer Barrier stabilizing effects of cAMP as well as of the small GTPase Rac 1 are well established. Moreover, it is generally believed that permeability-increasing mediators such as thrombin disrupt endothelial barrier functions primarily via activation of Rho A. In this study, we provide evidence that decrease of both cAMP levels and of Rac 1 activity contribute to thrombin-mediated barrier breakdown. Treatment of human dermal microvascular endothelial cells (HDMEC) with Rac 1-inhibitor NSC-23766 decreased transendothelial electrical resistance (TER) and caused intercellular gap formation. These effects were reversed by addition of forskolin/rolipram (F/R) to increase intracellular cAMP but not by the cAMP analogue 8-pCPT-2,-O-Methyl-cAMP (O-Me-cAMP) which primarily stimulates protein kinase A (PKA)-independent signaling via Epac/Rap 1. However, both F/R and O-Me-cAMP did not increase TER above control levels in the presence of NSC-23766 in contrast to experiments without Rac 1 inhibition. Because Rac 1 was required for maintenance of barrier functions as well as for cAMP-mediated barrier stabilization, we tested the role of Rac 1 and cAMP in thrombin-induced barrier breakdown. Thrombin-induced drop of TER and intercellular gap formation were paralleled by a rapid decrease of cAMP as revealed by fluorescence resonance energy transfer (FRET). The efficacy of F/R or O-Me-cAMP to block barrier-destabilizing effects of thrombin was comparable to Y27632-induced inhibition of Rho kinase but was blunted when Rac 1 was inactivated by NSC-23766. Taken together, these data indicate that decrease of cAMP and Rac 1 activity may be an important step in inflammatory barrier disruption. J. Cell. Physiol. 220: 716,726, 2009. © 2009 Wiley-Liss, Inc. [source] Synthesis and characterization of stable betainic pyrimidinaminidesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2002Andreas Schmidt Depending on electronically or kinetically stabilizing effects determined by the substitution pattern or the reaction conditions, 6-amino substituted (5-chloropyrimidine-2,4-diyl)bis(hetarenium) salts or 5-chloro-2,6-bis-(pyridinio)-pyrimidin-4-aminides are formed on nucleophilic substitution of 4-(dimethylamino)pyridine, 4-(pyrrolidin-1-yl)pyridine, or 1-methylimidazole on 4-amino substituted 2,5,6-trichloropyrimidines. [source] Evidence that WbpD is an N -acetyltransferase belonging to the hexapeptide acyltransferase superfamily and an important protein for O-antigen biosynthesis in Pseudomonas aeruginosa PAO1MOLECULAR MICROBIOLOGY, Issue 5 2005Cory Q. Wenzel Summary Di- N -acetylated uronic acid residues are unique sugar moieties observed in the lipopolysaccharides (LPS) of respiratory pathogens including several serotypes of Pseudomonas aeruginosa and several species of Bordetella. WbpD of P. aeruginosa PAO1 (serotype O5) is a putative 3- N -acetyltransferase that has been implicated in the biosynthesis of UDP-2,3-diacetamido-2,3-dideoxy- d -mannuronic acid [UDP- d -Man(2NAc3NAc)A], a precursor for the d -Man(2NAc3NAc)A residues in the B-band O antigen of this bacterium. A chromosomal knockout mutant of wbpD is incapable of producing either long-chain B-band O antigen (, 2 repeating units) or semi-rough LPS (lipid A-core + one repeat). Adding wbpD in trans restored LPS production to the wild-type level; this indicates that wbpD is important for biosynthesis of individual B-band O-antigen repeating units. WbpD contains left-handed beta-helical (L,H) structure as observed by Conserved Domain analysis and in silico secondary and tertiary structure predictions. This feature suggested that WbpD belongs to the hexapeptide acyltransferase (HexAT) superfamily of enzymes. WbpD was overexpressed as an N-terminally histidine-tagged fusion protein (His6,WbpD) and purified to >,95% purity. The protein was subjected to Far-UV circular dichroism spectroscopy, and the data revealed that WbpD contains left-handed helical structure, which substantiated in silico predictions made earlier. Results from SDS-PAGE, matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS), and gel filtration analyses indicated that His6 -WbpD has trimeric organization, consistent with the quaternary structure of HexATs. The binding of acetyl-CoA by WbpD was demonstrated by MALDI-TOF MS, suggesting that WbpD is an acetyltransferase that utilizes a direct-transfer reaction mechanism. Incubation of WbpD with acetyl-CoA significantly enhanced the stability of the protein and prevented precipitation over a course of 14 days. As a substrate for studying the enzymatic activity of WbpD is unavailable at present, a structure-based model for the L,H domain of WbpD was generated. Comparisons between this model and the L,H domains of known HexATs suggested that Lys136 plays a role in acetyl-CoA binding. A K136A site-directed mutant construct could only partially complement the wbpD knockout, and this mutation also reduced the stabilizing effects of acetyl-CoA, while a K136R mutation showed no discernible effect on complementation of the wbpD mutant or the stabilizing effects of acetyl-CoA on the purified mutant protein. A modified pathway was proposed for the biosynthesis of UDP- d -Man(2NAc3NAc)A, in which WbpD is involved in the catalysis of the fourth step by acting as a UDP-2-acetamido-3-amino-2,3-dideoxy- d -glucuronic acid 3- N -acetyltransferase. [source] How enrichment, ecosystem size, and their effects on species richness co-determine the stability of microcosm communitiesOIKOS, Issue 4 2010Wei Li Nutrient enrichment, ecosystem size, and richness each may directly affect the stability of both populations and communities. Alternatively, nutrient enrichment and ecosystem size each may directly affect richness, which in turn may affect stability. No previous studies, however, have tested empirically how these three factors interact and co-determine stability. We manipulated nutrient input and ecosystem size in replicate microcosms containing a diverse bacterial flora, and a range of green algae and heterotrophic protozoa, and used these manipulations and the resulting variation in species richness to measure their combined effects on temporal stability of both populations and communities. Results showed that nutrient enrichment and ecosystem size controlled protist richness, and their effects on stability could be mediated by richness. In addition, both community-level and population-level stability increased with protist richness. Furthermore, mean species evenness and mean species richness was negatively related. Effects of statistical averaging, overyielding, and component population stability were identified as possible mechanisms involved explaini ng the stabilizing effects of richness on community stability. Their relative strength in influencing stability, however, is likely to change as mean evenness decreased with increasing richness. This decrease in evenness would tend to weaken the strength of the statistic averaging effect, but increase the strength of the other two mechanisms due to relatively lower population variability (component population stability) and higher mean biovolumes of dominant protists (overyielding). [source] Do electrostatic interactions destabilize protein,nucleic acid binding?BIOPOLYMERS, Issue 2 2007Sanbo Qin Abstract The negatively charged phosphates of nucleic acids are often paired with positively charged residues upon binding proteins. It was thus counter-intuitive when previous Poisson,Boltzmann (PB) calculations gave positive energies from electrostatic interactions, meaning that they destabilize protein,nucleic acid binding. Our own PB calculations on protein,protein binding have shown that the sign and the magnitude of the electrostatic component are sensitive to the specification of the dielectric boundary in PB calculations. A popular choice for the boundary between the solute low dielectric and the solvent high dielectric is the molecular surface; an alternative is the van der Waals (vdW) surface. In line with results for protein,protein binding, in this article, we found that PB calculations with the molecular surface gave positive electrostatic interaction energies for two protein,RNA complexes, but the signs are reversed when the vdW surface was used. Therefore, whether destabilizing or stabilizing effects are predicted depends on the choice of the dielectric boundary. The two calculation protocols, however, yielded similar salt effects on the binding affinity. Effects of charge mutations differentiated the two calculation protocols; PB calculations with the vdW surface had smaller deviations overall from experimental data. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 112,118, 2007. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Alteration of inflammatory response following small-volume resuscitationBRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 7 2000F. Gebhard Background Small-volume resuscitation is rather effective in the primary volume treatment of major trauma. Blood pressure stabilizing effects occur immediately but last for a limited period only. Influences on inflammatory reactions in humans have not been reported so far. This prospective randomized study therefore analysed the inflammatory response in the very early (pre)clinical period after administration of crystalloids plus starch, hyperosmolar/hyperoncotic starch and lyophilized plasma solutions. Methods Upon approval of the ethics committee, 41 patients were enrolled with multiple injuries (injury severity score (ISS) mean 34 (range 9,75)). The patients received randomly either standard solutions, i.e. starch plus crystalloids (group C (control); n = 14), hyperosmolar/hyperoncotic starch (group S (small volume); n = 14) or lyophilized plasma (group L (lyoplasma); n = 13). Subsets were performed according to the different solutions as well as to the severity of trauma (ISS below 17, 18,31, 32 or more) and survivors/non-survivors. The first blood sample was obtained at the scene of the accident before cardiopulmonary resuscitation, when appropriate. Subsequently, blood samples were collected hourly. All samples were spun immediately at 4°C and stored at ,70°C. Interleukin (IL) 6 as well as several different prostaglandins (PGI2, thromboxane A2, PGE2) were determined to characterize the overall inflammatory response. Results Eleven casualties (seven men and four women, mean age 31 years) died because of major trauma within 24 h after the incident. In all patients IL-6 levels promptly increased within the first 2 h, most pronounced in patients with the severest trauma (ISS greater than 32) and non-survivors. Patients in groups C and S had a comparable time course of IL-6 plasma levels with a slightly higher release in minor injuries (ISS less than 30). The same was true for prostaglandins. In contrast, patients in group L had clearly higher IL-6 concentrations during the first 2,12 h, again most pronounced in those with the severest trauma (ISS greater than 32). Conclusion These results demonstrate that the early systemic inflammatory response after small-volume resuscitation is rather similar to that of patients infused with standard-volume therapy after trauma. In contrast, lyoplasma seems to increase the inflammatory response regardless of the injury severity. © 2000 British Journal of Surgery Society Ltd [source] Composite Particles of Novozyme,435 and Silicone: Advancing Technical Applicability of Macroporous Enzyme CarriersCHEMCATCHEM, Issue 4 2009Abstract The mechanical and leaching stability of enzymes adsorbed on macroporous carriers is an important issue for the technical applicability of such biocatalysts. Both can considerably benefit from the deposition of silicone coating on the carrier surface. The coating of the immobilized lipase Novozyme,435 (NZ435), as a model enzyme preparation, with different silicone loadings was studied in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by energy-dispersive X-ray spectroscopy (EDX) and BET isotherms, and offers explanations and prerequisites for its stabilizing effects. The deposition of silicone on the poly(methyl methacrylate) (PMMA) carrier was found to form an interpenetrating network composite rather than the anticipated core-shell structure. The silicone precursors homogeneously wet the carrier surface including all inner pores and gradually fill the complete carrier. In parallel, the surface area of NZ435 decreases from an initial value of 89,m2g,1to 0.2,m2g,1after silicone loading. A visible layer of silicone on the outer surface of the carrier was only observed at a silicone concentration of 54,%,w/w and more. Maximum leaching stability corresponds to the formation of this layer. The mechanical stability increases with the amount of deposited silicone. It can be expected that stabilization against leaching and/or mechanical stress by formation of silicone composites can easily be transferred to a whole range of alternative biocatalytic systems. This should considerably advance their general technical applicability and overall implementation of biocatalysts in chemical synthesis. [source] | ||||||||||||||||