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Improved Stability (improved + stability)
Selected AbstractsMiniature Biofuel Cells with Improved Stability Under Continuous OperationELECTROANALYSIS, Issue 19-20 2006Michael Abstract We have developed miniature biofuel cells (BFCs) with dimensions as small as 12×12×9,mm by adopting the design of stackable proton exchange membrane (PEM) fuel cells. The enzymatic anodes were constructed by using stabilized glucose oxidase (GOx) in the form of crosslinked enzyme clusters (CECs) on the surface of carbon nanotubes (CNTs). The combination of stabilized GOx and unbuffered fuel solution resulted in stabilized performance of miniature BFCs under continuous operation for more than 16 hours. This unprecedentedly high operational stability of miniature BFCs opens up new possibilities for many BFC applications. [source] Multitasking by Multivalent Circular DNA AptamersCHEMBIOCHEM, Issue 3 2006Daniel A. Di Giusto Abstract Nucleic acid aptamers are finding increasing applications in biology, especially as therapeutic candidates and diagnostic components. An important characteristic in meeting the needs of these applications is improved stability in physiological fluids, which is most often accomplished with chemical modification or unnatural nucleotides. In an alternative approach we have specified the design of a multivalent circular DNA aptamer topology that encompasses a number of properties relevant to nucleic acid therapeutic candidates, especially the ability to multitask by combining different activities together within a modular structure. Improved stability in blood products, greater conformational stability, antidoting by complementary circular antiaptamers, heterovalency, transcription factor decoy activity and minimal unintended effects upon the cellular innate immune response are desirable properties that are described here. Multitasking by circular DNA aptamers could similarly find applications in diagnostics and biomaterials, where the combination of interchangeable modules might generate new functions, such as anticoagulation coupled with reversible cell capture as, described here. These results provide a platform for further exploration of multivalent circular aptamer properties, especially in novel combinations of nucleic acid therapeutic modes. [source] Directed evolution of formate dehydrogenase from Candida boidinii for improved stability during entrapment in polyacrylamideFEBS JOURNAL, Issue 17 2006Marion B. Ansorge-Schumacher In two cycles of an error-prone PCR process, variants of formate dehydrogenase from Candida boidinii were created which revealed an up to 4.4-fold (440%) higher residual activity after entrapment in polyacrylamide gels than the wild-type enzyme. These were identified in an assay using single precursor molecules of polyacrylamide instead of the complete gel for selection. The stabilization resulted from an exchange of distinct lysine, glutamic acid, and cysteine residues remote from the active site, which did not affect the kinetics of the catalyzed reaction. Thermal stability increased at the exchange of lysine and glutamic acid, but decreased due the exchange of cysteine. Overall, the variants reveal very suitable properties for application in a technical synthetic process, enabling use of entrapment in polyacrylamide as an economic and versatile immobilization method. [source] Exogenously Applied Nitric Oxide Enhances the Drought Tolerance in Fine Grain Aromatic Rice (Oryza sativa L.)JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2009M. Farooq Abstract Drought stress is a severe threat to the sustainable rice production, which causes oxidative damage and disturbs plant water relations, while exogenously applied nitric oxide (NO) may have the potential to alleviate these effects in rice plants. In this study, the role of NO to improve drought tolerance in fine grain aromatic rice (Oryza sativa L. cv. Basmati 2000) was evaluated. Sodium nitroprusside, a NO donor, was used at 50, 100 and 150 ,mol l,1 both as seed priming and foliar spray. To prime, the seeds were soaked in aerated NO solution of respective solution for 48 h and dried back to original weight. Primed and non-primed seeds were sown in plastic pots with normal irrigation in a greenhouse. At four leaf stage, plants were subjected to drought stress except the controls, which were kept at full field capacity. Drought was maintained at 50 % of field capacity by watering when needed. Two controls were maintained; both receiving no NO treatments as foliar application or seed treatment, one under drought conditions and the other under well-watered conditions. Drought stress seriously reduced the rice growth, but both methods of NO application alleviated the stress effects. Drought tolerance in rice was strongly related to the maintenance of tissue water potential and enhanced capacity of antioxidants, improved stability of cellular membranes and enhanced photosynthetic capacity, plausibly by signalling action of NO. Foliar treatments proved more effective than the seed treatments. Among NO treatment, 100 ,mol l,1 foliar spray was more effective. [source] In vitro degradability and stability of hydrophobically modified pH-sensitive micelles using MPEG-grafted poly(,-amino ester) for efficient encapsulation of paclitaxelJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Min Sang Kim Abstract Methoxypoly(ethylene glycol)-grafted poly(,-amino ester) was synthesized for the fabrication of pH-sensitive micelles, and these micelles were modified with deoxycholic acid to facilitate the hydrophobic interaction between the micellar core and paclitaxel. The micelle properties were studied by dynamic light scattering and fluorescence spectrometry. An in vitro degradation study showed that the synthesized polymers degraded hydrolytically within 24 h under physiological conditions. The stability of paclitaxel-loaded pH-sensitive micelles was evaluated in vitro. The introduced deoxycholic acid more stabilized the micelles at pH 7.4 compared to the micelles without modification. But the pH-sensitive region of the micelles was lowered from pH 6.8 to pH 5.8. These results indicate that pH-sensitive micelles with improved stability have great potential as hydrophobic drug carriers for tumor targeting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Neuropathy-induced apoptosis: Protective effect of physostigmineJOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2009L. Di Cesare Mannelli Abstract Traumatic, infectious, metabolic, and chemical noxa to the nervous system are the etiology of a crippling disease generally termed neuropathy. Motor disorders, altered sensibility, and pain are the pathognomonic traits. Cellular alterations induced by this chronic pathology include mitochondrial dysfunctions that lead to the activation of the apoptotic cascade. Energy imbalance can compromise the maintenance of mitochondrial membrane potential, furthering the release of cytochrome C and the subsequent cleavage and activation of caspases. Chronic constriction injury (CCI) of the rat sciatic nerve is a neuropathy model able to induce a strong mitochondrial impairment with a consequent apoptotic induction. In this model, the acetylcholinesterase inhibitor physostigmine is administered at 0.125 mg/kg i.p. (twice per day) starting from the operation and for 15 days after. The cholinergic activation reduces cytosolic levels of cytochrome C, suggesting an improved stability of the mitochondrial membrane, and the expression level of the active caspase 3 fragments (19, 16 kDa) is reduced significantly with respect to saline treatment. Accordingly, physostigmine impairs caspase 3 protease activity. In fact, the target of the activated caspase 3, the 89-kDa PARP fragment, is significantly less expressed in the ligated nerve of physostigmine-treated rats, reaching levels that are comparable to those in the contralateral unligated nerve. Finally, this natural acetylcholinesterase inhibitor reduces DNA fragmentation both in the proximal and in the distal parts of the nerve. This protection correlates with the induction of XIAP. Therefore, apoptosis, central to tissue degeneration, is prevented by repeated physostigmine treatment of CCI animals. © 2009 Wiley-Liss, Inc. [source] A New Approach to the Deposition of Elemental Boron and Boron-Based Coatings by Pulsed Magnetron Sputtering of Loosely Packed Boron Powder TargetsPLASMA PROCESSES AND POLYMERS, Issue S1 2007Martynas Audronis Abstract Large numbers of potential application areas for elemental boron and boron-based thin film materials make this subject area a focus of significant scientific and industrial interest. Applications include thermoelectric energy conversion devices, biomedical implants, metalworking tools and automotive components. Boron is however also recognised widely to be a difficult-to-deposit material. Therefore, a new technique to deposit boron (and other boron-based materials) by pulsed magnetron sputtering of loosely packed powder targets has been proposed. Among the benefits of this approach are: improved stability of the deposition process, increased speed and flexibility of target preparation, enhanced time- and cost-effectiveness and the ability to control readily the target and hence the chemical composition of the coating. [source] Delay distribution based robust H, control of networked control systems with uncertainties,ASIAN JOURNAL OF CONTROL, Issue 1 2010Chen Peng Abstract Network induced delay in networked control systems (NCS) is inherently non-uniformly distributed and behaves with multifractal nature. However, such network characteristics have not been well considered in NCS analysis and synthesis. Making use of the information of the statistical distribution of NCS network induced delay, a delay distribution based stochastic model is adopted to link Quality-of-Control and network Quality-of-Service for NCS with uncertainties. From this model together with a tighter bounding technology for cross terms, H, NCS analysis is carried out with significantly improved stability results. Furthermore, a memoryless H, controller is designed to stabilize the NCS and to achieve the prescribed disturbance attenuation level. Numerical examples are given to demonstrate the effectiveness of the proposed method. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] A new crystal form of XT6 enables a significant improvement of its diffraction quality and resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2004Maya Bar Xylanases (1,4-,- d -xylan xylanhydrolases; EC 3.2.1.8) hydrolyze the 1,4-,- d -xylopyranosyl linkage of xylans. The detailed structural characterization of these enzymes is of interest for the elucidation of their catalytic mechanism and for their rational modification toward improved stability and specificity. An extracellular xylanase from Geobacillus stearothermophilus T-6 (XT6) has recently been cloned, overexpressed, purified and biochemically characterized. Previous crystallographic efforts resulted in a hexagonal crystal form, which subsequently proved to be of limited use for structural analysis, mainly because of its relatively poor diffraction quality and resolution. A systematic search for more suitable crystals of XT6 recently resulted in a new crystal form of this enzyme with significantly improved diffraction characteristics. The new crystals belong to a C -centred monoclinic crystal system (space group C2), with unit-cell parameters a = 121.5, b = 61.7, c = 89.1,Å, , = 119.7°. These crystals diffract X-rays to better than 1.5,Å resolution, showing a very clear diffraction pattern of relatively high quality. The crystals are mechanically strong and exhibit excellent radiation-stability when frozen under cold nitrogen gas. A full diffraction data set to 1.45,Å resolution (94.1% completeness, Rmerge = 7.0%) has been collected from flash-frozen crystals of the native enzyme at 95,K using synchrotron radiation. Crystals of the E159A/E265A catalytic double mutant of XT6 were found to be isomorphous to those of native XT6. They were used for a full measurement of 1.8,Å resolution diffraction data at 100,K (90.9% completeness; Rmerge = 5.0%). These data are currently being used for the high-resolution structure determination of XT6 and its mutant for mechanistic interpretations and rational introduction of thermostability. [source] Rapid optimization of protein freeze-drying formulations using ultra scale-down and factorial design of experiment in microplatesBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Yitzchak Grant Abstract Retaining biopharmaceutical proteins in a stable form is critical to their safety and efficacy, and is a major factor for optimizing the final product. Freeze-dried formulations offer one route for improved stability. Currently the optimization of formulations for freeze-drying is an empirical process that requires many time-consuming experiments and also uses large quantities of product material. Here we describe a generic framework for the rapid identification and optimization of formulation excipients to prevent loss of protein activity during a lyophilization process. Using factorial design of experiment (DOE) methods combined with lyophilization in microplates a range of optimum formulations were rapidly identified that stabilized lactose dehydrogenase (derived from Lactobacillus leichmanii) during freeze-drying. The procedure outlined herein involves two rounds of factorially designed experiments,an initial screen to identify key excipients and potential interactions followed by a central composite face designed optimization experiment. Polyethylene glycol (PEG) and lactose were shown to have significant effects on maintaining protein stability at the screening stage and optimization resulted in an accurate model that was used to plot a window of operation. The variation of freezing temperatures and rates of sublimation that occur across a microplate during freeze-drying have been characterized also. The optimum formulation was then freeze-dried in stoppered vials to verify that the microscale data was relevant to the effects observed at larger pilot scales. This work provides a generic approach to biopharmaceutical formulation screening where possible excipients can be screened for single and interactive effects thereby increasing throughput while reducing costs in terms of time and materials. Biotechnol. Bioeng. 2009; 104: 957,964. © 2009 Wiley Periodicals, Inc. [source] Enzyme immobilization via silaffin-mediated autoencapsulation in a biosilica supportBIOTECHNOLOGY PROGRESS, Issue 2 2009Wesley D. Marner II Abstract Enzymes and other biomolecules are often immobilized in a matrix to improve their stability or to improve their ability to be reused. Performing a polycondensation reaction in the presence of a biomolecule of interest relies on random entrapment events during polymerization and may not ensure efficient, homogeneous, or complete biomolecule encapsulation. To overcome these limitations, we have developed a method of incorporating autosilification activity into proteins without affecting enzymatic functionality. The unmodified R5 silaffin peptide from Cylindrotheca fusiformis is capable of initiating silica polycondensation in vitro at ambient temperatures and pressures in aqueous solution. In this study, translational fusion proteins between R5 and various functional proteins (phosphodiesterase, organophosphate hydrolase, and green fluorescent protein) were produced in Escherichia coli. Each of the fusion proteins initiated silica polycondensation, and enzymatic activity (or fluorescence) was retained in the resulting silica spheres. Under certain circumstances, the enzymatically-active biosilica displayed improved stability relative to free enzyme at elevated temperatures. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Mechanism Exploration during Lipase-Mediated Methanolysis of Renewable Oils for Biodiesel Production in a tert -Butanol SystemBIOTECHNOLOGY PROGRESS, Issue 5 2007Wei Du tert -Butanol has been developed as a novel reaction medium for lipase-mediated methanolysis of renewable oils for biodiesel production, in which lipase could maintain high catalytic activity, although the logP value of tert -butanol was just about 0.35. The related mechanism exploration has been carried out, and it has been proposed first in this manuscript that in the biodiesel production system, log Penvironment (log Penvironment = xmethanol log Pmethanol + xoils log Poils + xsolvent log Psolvent) including reactants and organic solvent should be taken into account to consider the effect of the whole environment on lipase activity instead of just considering the effect of the organic solvent itself. Further study showed that the operational stability of the lipase could be improved significantly in this system and there was no loss in lipase activity even after its being continuously used for 200 batches. The phase diagrams of the ternary-components tert -butanol/methanol/rapeseed oils were plotted further, and it was found that the methanol tolerance was the saturated methanol concentration in the system. It was demonstrated first here that the improved stability of the lipase was due to the elimination of negative effects caused by methanol and byproduct glycerol in the tert -butanol system. [source] Investigation of the Substrate Specificity of Lacticin 481 Synthetase by Using Nonproteinogenic Amino AcidsCHEMBIOCHEM, Issue 5 2009Matthew R. Levengood Abstract One enzyme, many substrates. The substrate specificity of a lantibiotic biosynthetic enzyme, lacticin 481 synthetase, was probed by using synthetic prepeptides containing a variety of nonproteinogenic amino acids, including unnatural ,-amino acids, ,-amino acids, D -amino acids, and peptoids. Lantibiotics are peptide antimicrobial compounds that are characterized by the thioether-bridged amino acids lanthionine and methyllanthionine. For lacticin 481, these structures are installed in a two-step post-translational modification process by a bifunctional enzyme, lacticin 481 synthetase (LctM). LctM catalyzes the dehydration of Ser and Thr residues to generate dehydroalanine or dehydrobutyrine, respectively, and the subsequent intramolecular regio- and stereospecific Michael-type addition of cysteines onto the dehydroamino acids. In this study, semisynthetic substrates containing nonproteinogenic amino acids were prepared by expressed protein ligation and [3+2]-cycloaddition of azide and alkyne-functionalized peptides. LctM demonstrated broad substrate specificity toward substrates containing ,-amino acids, D -amino acids, and N -alkyl amino acids (peptoids) in certain regions of its peptide substrate. These findings showcase its promise for use in lantibiotic and peptide-engineering applications, whereby nonproteinogenic amino acids might impart improved stability or modulated biological activities. Furthermore, LctM permitted the incorporation of an alkyne-containing amino acid that can be utilized for the site-selective modification of mature lantibiotics and used in target identification. [source] A Novel Genetic Selection System for Improved Enantioselectivity of Bacillus subtilis Lipase ACHEMBIOCHEM, Issue 7 2008Ykelien L. Boersma Dr. Abstract In directed evolution experiments, success often depends on the efficacy of screening or selection methods. Genetic selections have proven to be extremely valuable for evolving enzymes with improved catalytic activity, improved stability, or with altered substrate specificity. In contrast, enantioselectivity is a difficult parameter to select for. In this study, we present a successful strategy that not only selects for catalytic activity, but for the first time also for enantioselectivity, as demonstrated by the selection of Bacillus subtilis lipase A variants with inverted and improved enantioselectivity. A lipase mutant library in an aspartate auxotroph Escherichia coli was plated on minimal medium that was supplemented with the aspartate ester of the desired enantiomer (S)-(+)-1,2- O -isopropylidene- sn -glycerol. To inhibit growth of less enantioselective variants, a covalently binding phosphonate ester of the opposite (R)-(,)-1,2- O -isopropylidene- sn -glycerol enantiomer was added as well. After three selection rounds in which the selection pressure was increased by raising the phosphonate ester concentration, a mutant was selected with an improved enantioselectivity increased from an ee of ,29.6,% (conversion 23.4,%) to an ee of +73.1,% (conversion 28.9,%) towards the (S)-(+)-enantiomer. Interestingly, its amino acid sequence showed that the acid of the catalytic triad had migrated to a position further along the loop that connects ,7 and ,E; this shows that the position of the catalytic acid is not necessarily conserved in this lipase. [source] | ||||||||||||||||