bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactor Performance in the Presence of Catalyst Deactivation
Authors: Flaschel E. 
Published: March 2006

AbstractThe main variable of enzymatic processes is often found to be the operating temperature. An increase in temperature leads to higher rates for the catalytic transformation. However, beyond a certain temperature catalyst deactivation is winning the game. Therefore, processes should be optimized in order to determine the temperature which leads to a minimal demand of enzyme preparation. For the prediction of such optimal reactor operation, modeling of the temperature dependence of the process has to be performed. Examples of such modeling are given for the hydrolysis of lactose in UHT milk by means of three different β‐galactosidases – those from Aspergillus oryzae, Kluyveromyces lactis, and Escherichia coli. The reaction kinetics for a constant initial lactose concentration can be described by a model of two parameters, of which only one depends on temperature. For the lactase of E. coli the reaction can be described as a simple reaction with first order kinetics. The deactivation mechanism includes a reversible as well as an irreversible path of denaturation. The temperature dependent parameters follow Arrhenius' and van't Hoff's law, respectively. On the basis of their particular reaction models all three enzymes can be compared with respect to their optimum use. The models have been verified under laboratory conditions and have shown their usefulness for the prediction of optimum operating variables. Quite remarkable features have been found for the lactase of E. coli.
Optimization and Control of Industrial Microbial Cultivation Processes
Authors: Jenzsch M. , Simutis R. , Lübbert A. 
Published: March 2006

AbstractCompared to the immense achievements in fundamental molecular biological sciences, the improvements in the fermentation and downstream processing technologies used in industry have been less spectacular over the last decade. Hence, there is a misbalance between new cellular systems and production technologies, resulting in a decreasing annual rate of approved production processes. In its PAT initiative the U.S. Food and Drug Administration identifies the potential for continuous improvement and makes concrete suggestions how this can be achieved. Here, some of these suggestions were applied to recombinant protein production with Escherichia coli and Pichia pastoris cultures. Concretely, the development of process operational procedures is discussed that allow a more tight supervision of the processes and the automatic control in cases where processes deviate from their set‐point profiles.
Optimization of Reaction Parameters and Cultivation Conditions for Biocatalytic Hydrogen Transfer Employing Overexpressed ADH‐‘A’ from Rhodococcus ruber DSM 44541 in E. coli
Authors: Edegger K. , Gruber C. C. , Faber K. , Hafner A. , Kroutil W. 
Published: March 2006

AbstractThe alcohol dehydrogenase ADH‐‘A’ from Rhodococcus ruber DSM 44541 represents a highly efficient catalyst for biocatalytic hydrogen transfer reactions. Starting from an exceedingly low level of active ADH‐‘A’ in Escherichia coli, the apparent specific activity of ADH‐‘A’ overexpressed in E. coli cells could be drastically enhanced by a factor of 550 by optimizing the host and induction/growth conditions. The influence of reaction parameters like pH, cosubstrate (2‐propanol, acetone) concentration, substrate concentration temperature and additional cofactor on the apparent activity was investigated. In contrast to the purified enzyme, the pH optimum for oxidation and reduction were identical. Due to the employment of whole cells of E. coli/ADH‐‘A’ as catalyst lower operational stability was found.
Reaction Engineering Aspects of Microbial Mercury Removal
Authors: Leonhäuser J. , Röhricht M. , Wagner‐Döbler I. , Deckwer W.‐D. 
Published: March 2006

AbstractMercury‐resistant microorganisms are widespread in natural environments and can effectively be used to demercurize Hg(II)‐contaminated wastewaters as was already demonstrated on an industrial scale. The aim of this paper is to find the performance limits with regard to Hg(II) loadings D cHg,in (dilution rate × Hg(II) inlet concentration) and residual Hg(II) at the reactor outlet and to provide a reasonable basis for an optimal and safe process design. To this end, comprehensive studies were carried out with different single microbes (natural isolates and a genetically engineered strain) as well as microbial consortia in batch and continuous stirred reactors and fixed beds with microorganisms immobilized as films. The rate of the biotransformation (reduction of inorganically and organically bound Hg(II) to elemental Hg(0)) was found to follow a uniform mechanism with inhibition kinetics (Haldane type). Both reactor types are able to cope with high Hg(II) loadings and yield conversions up to 98 %. The stirred vessel is particularly suited for high cHg,in but restricted to low D (D < μmax), while the fixed bed can be operated at high D, say 10 h–1, but can only deal with cHg,in < 10 mg/L due to the limited Hg(II) tolerance of microorganisms. The loading limitations can be removed by appropriate recycle flows for both reactor types. However, irrespective of reactor type used, the residual Hg at the outlet cannot be reduced below the legal discharge limit (50 μg/L) mainly owing to the adsorption of Hg(II) on biomass. Therefore, a separation step following the reactor is required (sand bed, activated carbon filter). Comparing the reactor types exhibits the superiority of the fixed bed system due to its simpler construction, easier operation and higher cost effectiveness. Furthermore, the fixed bed shows better flexibility and robustness to extreme loadings. This justifies a posteriori the choice of a fixed bed reactor applied in the technical process.
Easy Access to Enantiomerically Pure Nonproteinogenic Amino Acids
Authors: Laumen K. , Ghisalba O. 
Published: March 2006

AbstractThe protease from Bacillus licheniformis (alcalase) shows a remarkable broad substrate tolerance and high enantioselectivity against nonproteinogenic racemic amino acid derivatives. N‐acetyl protected amino acid esters of mono‐, di‐ or tri‐substituted phenyl alanines and even tert.‐leucine were hydrolyzed with high enantioselectivity. The obtained mixtures of (S)‐N‐acetyl amino acid and (R)‐N‐acetyl amino acid ester can easily be separated. The R‐ or S‐amino acids were obtained by acidic cleavage of the optically pure derivatives or the (R)‐ester was racemized by treatment with potassium t‐butylate.
Selective Recovery of Carbohydrates from Aqueous Solution Facilitated by a Carrier
Authors: Hameister D. , Kragl K. 
Published: March 2006

AbstractCarbohydrate recovery is an active area of supramolecular chemistry, motivated by the biological importance of saccharides as well as the unusual challenge presented by these complex substances. The recovery of carbohydrates from aqueous media is a difficult separation problem due to the large, irregular and multivalent structure and the low solubility of carbohydrates in organic solvents. A method for the selective recovery of mono‐ and disaccharides from aqueous media has been developed. The use of different organic solvents like butanol, methyl tertiary‐butyl ether (MTBE), n‐hexane or toluene for liquid‐liquid extraction of carbohydrates was investigated. This extraction process is facilitated by a carrier, i.e., primary amines such as cyclooctylamine. The influence of different parameters (temperature, amine concentration, extraction time) on the efficiency of the extraction was studied. Recovery rates up to 40 % are possible in a one‐stage process. Selectivities range from 1.3 up to 875.4.
Electroenzymatic Synthesis of Chiral Sulfoxides
Authors: Kohlmann C. , Lütz S. 
Published: March 2006

AbstractChloroperoxidase (CPO) from Caldariomyces fumago (E.C. 1.11.1.10) is able to enantioselectively oxidize various sulfides to the corresponding (R)‐enantiomer of the sulfoxides. For these oxidations the enzyme requires an oxidant. Most commonly, tert‐butyl hydroperoxide (TBHP) and hydrogen peroxide are used. As it is known that these oxidants inactivate the enzyme, the enzymatic reaction was combined with the electrochemical in situ generation of hydrogen peroxide. As substrates for this combination of an enzymatic and an electrochemical reaction methyl p‐tolyl sulfide, 1‐methoxy‐4‐(methylthio)benzene and N‐MOC‐L‐methionine methyl ester were used to carry out batch experiments.
Horseradish Peroxidase Combined With Oxidase Enzymes a Valuable Bioanalytical Tool: Lactate Oxidase – A Case Study
Authors: Vojinovic V. , Bertin L. , Cabral J. M. S. , Fonseca L. P. 
Published: March 2006

AbstractEnzymatic biosensors have been extensively investigated for real‐time bioprocess monitoring and other online analysis. However, implementation of biosensors has been strongly hindered by their limited stability. This work reports a significant improvement of the stability of the immobilized oxidases by in situ reduction of the harmful H2O2. Thus, stabilized oxidases can serve as the basis for ethanol, glucose, and lactate sensors, with the ability to operate for long periods of time with virtually no change in activity. As an example, a lactate sensor, containing lactate oxidase aimed for bioprocess monitoring, has been described and characterized. Operational stabilities that allow up to 8 h continuous lactate conversion with virtually no activity loss have been achieved. The described system based on the in situ stabilization strategy is a promising new tool for the development of online analyses.
Comparative Study of Cyanobacteria as Biocatalysts for the Asymmetric Synthesis of Chiral Building Blocks
Authors: Havel J. , Weuster‐Botz D. 
Published: March 2006

AbstractThe three representative cyanobacteria, Synechococcus PCC7942, Anabaena variabilis, and Nostoc muscorum, were studied for their ability to asymmetrically reduce the prochiral ketones 2′‐3′‐4′‐5′‐6′‐pentafluoroacetophenone, ethyl 4‐chloroacetate, 4‐chloroacetophenone, and ethylbenzoylacetate to the corresponding chiral alcohols. Photosynthesis as well as respiration was applied for intracellular regeneration of the NAD(P)H cofactor. It was shown for the first time that all cyanobacteria were able to reduce the prochiral ketones asymmetrically without light for cofactor regeneration. By comparison of the cell specific product formation capacities of cyanobacteria with typical heterotrophic whole cell biocatalysts in batch processes, it is shown that comparable or, in some cases, better performances at high enantiomeric excess (ee > 99.8 %) are obtained. As a consequence of a generally strong product inhibition, in situ product removal must be applied in order to restore process efficiency when using cyanobacteria as biocatalysts.
From Enzyme Kinetics to Metabolic Network Modeling – Visualization Tool for Enhanced Kinetic Analysis of Biochemical Network Models
Authors: Oldiges M. , Noack S. , Wahl A. , Qeli E. , Freisleben B. , Wiechert W. 
Published: March 2006

AbstractModel‐based analysis of enzyme kinetics allows the determination of optimal conditions for their use in biocatalysis. For biotransformations or fermentative approaches the modeling of metabolic pathways or complex metabolic networks is necessary to obtain model‐based predictions of steps which limit product formation within the network. To set up adequate kinetic models, relevant mechanistic information about enzyme properties is required and can be taken from in vitro studies with isolated enzymes or from in vivo investigations using stimulus‐response experiments which provide a lot of kinetic information about the metabolic network. But with increasing number of reaction steps and regulatory interdependencies in the network structure the amount of simulation data dramatically increases and the simulation results from the dynamic models become difficult to analyze and interpret. Demonstrated for an Escherichia coli model of the central carbon metabolism, methods for visualization and animation of simulation data were applied and extended to facilitate model analysis and biological interpretation. The dynamic metabolite pool and metabolic flux changes were visualized simultaneously by a software tool. In addition, a new quantification method for enzyme activation/inhibition was proposed, and this information was implemented in the metabolic visualization.
Evaluation of the AERMOD dispersion model as a function of atmospheric stability for an urban area
Authors: Kumar Ashok , Dixit Shobhit , Varadarajan Charanya , Vijayan Abhilash , Masuraha Anand 
Published: March 2006

AbstractThe AERMOD dispersion model was used to compute ambient air concentrations of SO2 for 1‐, 3‐, and 24‐h averaging periods using the emission inventory data for Lucas County, Ohio for the year 1990. The estimated concentrations were classified based on the stability parameter, Monin–Obukhov length (L), for the two monitoring stations located in the area. The data were divided into two atmospheric stability classes (stable and convective cases) as used in the AERMOD model. These categories were further grouped into five subcategories based on the value of L to learn about fine details of model performance. The model evaluation was done using several statistical parameters used in air quality studies.AERMOD did not yield a satisfactory performance in predicting 1‐ and 3‐h average concentrations for the multisource region but showed a slightly better performance in predicting the 24‐h concentrations using urban option for the land use parameters. The model had a tendency to underpredict in both the stable and convective cases. In the 24‐h averaging period factor of two (Fa2) values suggested a better performance than fractional bias (FB). The model seemed to perform better for the Main Street station than the Collins Park station. Limited analysis using different land use parameters reported in the paper indicates that model performance may improve for certain cases. Other errors include the unavoidable scatter arising from differences between wind direction and actual transport for an averaging period, formulation of the model, and the emission inventory. The results of the study should be used cautiously because of the limited scope of the evaluation. Future work should focus on the role of land use parameters in predicting concentrations at the monitors and finding ways to quantify errors attributed to other factors. However, it is clear that more guidance is needed to apply the AERMOD model for multisource regions. Alternative schemes to divide the data should also be considered for analyzing model performance. © 2006 American Institute of Chemical Engineers Environ Prog, 2006
Evolution of channel morphology and hydrologic response in an urbanizing drainage basin
Authors: Nelson Peter A. , Smith James A. , Miller Andrew J. 
Published: March 2006

AbstractThe Dead Run catchment in Baltimore County, Maryland, has undergone intense urbanization since the late 1950s. Reconstruction of the channel planform from topographic maps dating back to the 1890s and aerial photographs dating back to the 1930s indicates that the channel has remained stable in planform since at least the 1930s. The relative stability of Dead Run contrasts with the alterations in channel morphology reported for other urbanizing streams in the Piedmont physiographic province of the eastern United States. Trend analyses of discharge records in Dead Run show that urban development and stormwater control measures have had significant impacts on the hydrologic response of the catchment. The flood hydraulics of the Dead Run catchment are examined for the event that occurred on 22 June 1972 in association with Hurricane Agnes. A two‐dimensional hydraulic model, TELEMAC‐2D, was used with a finite‐element mesh constructed from a combination of high‐resolution LiDAR topographic data and detailed field survey data to analyse the distribution of boundary shear stress and unit stream power along the channel and floodplain during flooding from Hurricane Agnes. The spatial and temporal distributions of these parameters, relative to channel gradient and channel/valley bottom geometry, provide valuable insights on the stability of the Dean Run channel. The stability of Dead Run's channel planform, in spite of extreme flooding and decades of urban development, is most likely linked to geological controls of channel and floodplain morphology. Copyright © 2006 John Wiley & Sons, Ltd.
River system discontinuities due to lateral inputs: generic styles and controls
Authors: Ferguson Robert I. , Cudden Judith R. , Hoey Trevor B. , Rice Stephen P. 
Published: March 2006

AbstractIn alluvial river systems, lateral inputs of water and/or sediment at junctions or undercut hillsides can disrupt what would otherwise be smooth downstream trends in mainstream bed elevation, channel gradient, and bed grain size. Generic styles of mainstream response to lateral inputs are investigated using a one‐dimensional sediment routing model with multiple grain size fractions. Numerical experiments isolate the effects of three para‐meters: ratio of tributary to mainstream water flux (QR), ratio of tributary to mainstream bedload flux (FR), and ratio of tributary to mainstream bedload diameter (DR). The findings are not unduly sensitive to the choice of initial conditions or to approximations made in the model. The primary distinction is between junctions that aggrade, causing local profile convexity with interrupted downstream fining, and junctions that degrade. The immediate effects of aggradation extend further upstream than downstream, whereas degradation is much more subdued and has no upstream impact. Aggradation is typical of coarse inputs (DR > 2), and degradation of fine inputs (DR < 1), but very high ratios of QR to FR also promote degradation. Both aggrading and degrading junctions can lead to a change in mainstream bed grain size well below the junction, with higher ratios of QR to FR producing a coarser distal bed. The effect of a tributary reflects the interplay between additional bed load and additional discharge to transport it. Copyright © 2006 John Wiley & Sons, Ltd.
Structure of flow over alluvial bedforms: an experiment on linking field and laboratory methods
Authors: Sukhodolov Alexander N. , Fedele Juan J. , Rhoads Bruce L. 
Published: March 2006

AbstractThis paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time–space averaging approach. Measurements of turbulence were obtained in a small river in Illinois, USA, over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica. Flow structure over the artificial bedform is similar to that observed in laboratory studies, but is markedly different from the flow structure over natural bedforms. These differences are most pronounced in the roughness sublayer, whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity. The double time–space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms. Mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests. However, vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms. Thus, despite the absence of flow separation, wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence. Copyright © 2006 John Wiley & Sons, Ltd.
Helicobacter pylori CagA—a bacterial intruder conspiring gastric carcinogenesis
Authors: Hatakeyama Masanori 
Published: March 2006

AbstractInfection with cagA‐positive Helicobacter pylori (H. pylori) is associated with the development of gastric adenocarcinoma. The cagA gene product CagA is delivered from the bacterium into the cytoplasm of the bacterium‐attached gastric epithelial cell via the type‐IV secretion system. Upon membrane localization and subsequent tyrosine phosphorylation by Src family kinases, translocated CagA functions as a scaffolding adaptor that interacts with a number of host proteins involved in cell signaling in both tyrosine phosphorylation‐dependent and ‐independent manners. Of special interest is the interaction of CagA with the SHP‐2 tyrosine phosphatase, of which gain‐of‐function mutations have recently been found in human malignancies. Through the complex formation, SHP‐2 is catalytically activated and induces morphological transformation that is associated with increased cell motility. In addition to the perturbation of intracellular signaling, CagA disrupts the apical junctional complex that regulates the cell–cell contact and maintains the integrity of the epithelial structure. These CagA activities may collectively cause cellular dysfunctions that promote accumulation of multiple genetic changes involved in malignant transformation. Further elucidation of host cell signaling targeted by CagA should provide a new paradigm for ‘bacterial carcinogenesis’ and also give insights into general understanding of inflammation‐mediated cancers. Clinically, detailed studies on the relationship between structural diversity and degree of pathogenic activity of CagA should make it possible to identify a high‐risk group for gastric carcinoma among H. pylori‐infected populations through cagA genotyping. © 2006 Wiley‐Liss, Inc.
Understanding urothelial carcinoma through cancer pathways
Authors: Schulz Wolfgang A. 
Published: March 2006

AbstractUrothelial carcinoma (UC), the common histological subtype of bladder cancer, presents as a papillary tumor or as an invasive, often lethal form. To study UC molecular biology, candidate gene and genome‐wide approaches have been followed. Here, it is argued that a ‘cancer pathway’ perspective is useful to integrate findings from both approaches. According to this view, papillary cancers typically exhibit activation of the MAPK pathway, as a consequence of oncogenic mutations in FGFR3 or HRAS, with increased Cyclin D1 expression. In contrast, invasive UC are characterized by severe disturbances in proximate cell cycle regulators, e.g. RB1 and CDKN2A/p16INK4A, which decrease dependency on mitogenic signaling. In addition, these disturbances permit, promote and are in turn exacerbated by chromosomal instability, which is further enhanced by loss of TP53 function. In another vicious cycle, defective cell cycle regulation interacts with DNA methylation alterations. The transition toward invasive UC may require concomitant and interacting defects in cell cycle regulation and the control of genomic stability. Intriguingly, neither canonical WNT/β‐Catenin nor hedgehog signaling appear to play major roles in UC. This may reflect its origin from more differentiated urothelial cells possessing a high regenerative potential rather than a stem cell population. © 2006 Wiley‐Liss, Inc.