bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamic shear stress and mass transport modulation of endothelial cell metabolism
Authors: Nollert M. U. , Diamond S. L. , McIntire L. V. 
Published: December 2004

AbstractMammalian cells responds to physical forces by altering their growth rate, morphology, metabolism, and genetic expression. We have studied the mechanism by which these cells detect the presence of mechanical stress and convert this force into intracellular signals. As our model systems, we have studied cultured human endothelial cells, which line the blood vessels and forms the interface between the blood and the vessel wall. These cell responds within minutes to the initiation of flow by increasing their arachidonic acid metabolism and increasing the level of the intracellular second messengers inositol trisphosphate and calcium ion concentration. With continued exposure to arterial levels of wall shear stress for up to 24 h, endothelial cells increase the expression of tissue plasminogen activator (tPA) and tPA messenger RNA (mRNA) and decrease the expression of endothelin peptide and endothelin mRNA. Since the initiation of flow also causes enhanced convective mass transfer to the endothelial cell monolayer, we have investigated the role of enhanced convection of adenosine trisphosphate (ATP) to the cell surface in eliciting a cellular response by monitoring cytosolic calcium concentrations on the single cell level and by computing the concentration profile of ATP in a parallel‐plate flow geometry. Our result demonstrate that endothelial cells respond in very specific ways to the initiation of flow and that mass transfer and fluid shear stress can both play a role in the modulation of intracellular signal transduction and metabolism.
Properties of microfiltration membranes: Flux loss during constant pressure permeation of bovine serum albumin
Authors: Bowen W. Richard , Gan Quan 
Published: December 2004

AbstractAn experimental study of permeation of dilute BSA solutions (filtration) at microfiltration membranes has been carried out. Most measurements were made with capillary pore aluminum oxide membranes, with some comparative measurements with tortuous and capillary pore polymeric membranes. In all cases, a continuous and substantial decrease in the rate of permeation with time was observed. This decrease in permeation with time was observed. This decrease in permeation rate was due neither to concentration polarization nor to protein adsorption alone. However, it could be quantified using the standard blocking filtration law, which describes a decrease in pore volume due to deposition of protein on the walls of the pore. The maximum calculated thickness of the deposited layers was 55nm on the walls of 200‐nm diameter pores. This phenomenon is quite different to adsorption of protein at such surfaces, this latter giving only sub‐monolayer or monolayer protein coverage under the conditions studied.
Lipase kinetics: Hydrolysis of triacetin by lipase from Candida cylindracea in a hollow‐fiber membrane reactor
Authors: Guit R. P. M. , Kloosterman M. , Meindersma G. W. , Mayer M. , Meijer E. M. 
Published: December 2004

AbstractThe aptitude of a hollow‐fiber membrane reactor to determine lipase kinetics was investigated using the hydrolysis of triacetin catalyzed by lipase from Canadida cylindracea as a model system. The binding of the lipase to the membrane appears not to be very specific (surface adsorption), and probably its conformation is hardly altered by immobilization, resulting in an activity comparable to that of the enzyme in its native form. The reaction kinetics defined on the membrane surface area were found to obey Michaelis‐Menten kinetics. The specific activity of the lipase in the membrane reactor was found to be significantly higher than in an emulsion reactor. The activity and stability of the enzyme immobilized on a hydrophilic membrane surface seem not to be influenced significantly by the choice of the membrane material. The hollow‐fiber membrane reactor is a suitable tool to assess lipase kinetics in a fast and convenient way.
Dynamics of induced CAT expression in E. coli
Authors: Bentley William E. , Davis Robert H. , Kompala Dhinakar S. 
Published: December 2004

AbstractThe dynamics of chemically induced chloramphenicolaceyl‐transferase (CAT) expression are determined in batch cultures of Escherichia coli DH5αF'IQ [pKK262‐1]. This article is directed towards understanding the coupling of induced cloned‐protein synthesis and reduced cell growth which are balanced in the optimal system. Experimental results indicate that the best inducer (IPTG) concentration is near 1.0 mM when added during midexponential growth. Lower concentrations cause only weak induction, whereas higher concentrations cause sufficiently strong induction that cell growth is suppressed. Induction at the onset of the stationary phase results in high expression but is accompanied by stimulated protease activity. Also, cell mass yield is adversely affected by enhanced protein synthesis. A structured metabolic model is shown to predict the responses of instantaneous growth rate and productivity which result from protein overexpression. This model can be employed to predict alternative reactor strategies and operating conditions necessary for the design of efficient bioprocess.
Long‐term perfusion culture of hybridoma: A “grow or die” cell cycle system
Authors: de la Broise Denis , Noiseux Manon , Lemieux Réal , Massie Bernard 
Published: December 2004

AbstractIn order to elucidate the hybridoma life cycle and the limiting factors in perfusion systems, we performed cultures in a stirred tank bioreactor, coupled to an external tangential flow filtration unit. Cell density and antibody production in perfusion were consistent with previous studies. The average life span of the cells (2.1–2.2 days), antibody, productivity per cell produced (30–38 mg/109 cells) and cell size diameter evolution appeared similar to values observed in batch cultures. These observations highly suggest a similar “grow or die” life cycle. Cell and antibody production, strictly related to the medium perfusion rate, seem to be under the control of the nutrient availability. A hypothesis to explain such a life cycle of hybridoma cells in perfusion systems and a model for viable and dead cell density is proposed.
Differential product release (DPR) of proteins from yeast: A new technique for selective product recovery from microbial cells
Authors: Huang R.‐B. , Andrews B. A. , Asenjo J. A. 
Published: December 2004

AbstractA novel method has been developed for the separation of bioproducts from yeast cells. The method uses a combination of physical, chemical, and biological agents such as lytic enzymes, osmotic supports, and spheroplast stabilizers. Using this technique, products (proteins and enzymes) can be released from specific cell locations at different process states; it has thus been celled differential product release (DPR). The wall‐associated proteins are released first and the lytic enzyme is removed together with the wall proteins at this stage. Secondly, the cytosol products are released by a mild procedure during which the organelles remained intact. Finally, the organelle proteins are solubilized. In each stage, specific proteins are released while others are kept inside the different cell compartments. This method can be used with relatively high yeast concentrations (up to 145 g dry wt/L) and gives higher product recoveries and much higher selectivity than mechanical disruption.
Protein partitioning at the isoelectric point: Influence of polymer molecular weight and concentration and protein size
Authors: Forciniti D. , Hall C. K. , Kula M. R. 
Published: December 2004

AbstractWe report the partition coefficient, Kp′ at the isoelectric point of lysozyme, chymotrypsinogen A, albumin, transferrin, and catalase in 64 different polyethylene(PEG)/ dextran(Dx)/water systems. We study the trends of the partition coefficient with protein type, polymer concentration, and polymer molecular weight. We find that the partition coefficient decreases with increasing tie line length for lysozyme, albumin, transferrin, and catalase for which Kp is less than 1, but increases for chymotrysinogen for which Kp is larger than 1. The effect of the tie line length on the partition coefficient is larger for the large proteins than for the small proteins. The partition coefficient decreases with increasing protein molecular weight except for lysozyme suggesting that lysozyme is present as a dimer or a trimer. The partition coefficient decreases with increasing PEG molecular weight, but the magnitude of the increase is larger for the smaller PEG molecular eights and tends to level of at high PEG molecular weight. The partition coefficient increases with increasing dextran (Dx) molecular weight for chymotrypsinogen but decreases for catalase. The partition coefficients of lysozyme, albumin, and transferrin increase with increasing Dx molecular weight from Dx 104 to Dx 1.1 × 105 and then slightly decrease from Dx 1.1 × 105 to Dx 5 × 105. The experimental results are analyzed using a statistical thermodynamics model. The experimental results are analyzed using a statistical thermodynamics model. The experiments suggest that protein partitioning at the isoelectric point in aqueous two‐phase systems is strongly related to the size of the proteins and polymers. Finally, the impossibility of obtaining data completely independent of polymer concentration is emphasized.
Inactivation and stabilization of stabilisins in neat organic solvents
Authors: Schulze Birgit , Klibanov Alexander M. 
Published: December 2004

AbstractThe stability of the serine proteases from Bacillus amyloliquefaciens (subtillisin BPN') and Bacillus licheniformis (subtilisin Carlsberg) was investigated in various anhydrous solvents at 45°C. The half‐life of subtilisin BPN' in dimethyl‐formamide dramatically depends on the pH of the aqueous solutions from which the enzyme was lyophilized, increasing from 48 min to 20 h when the pH is raised from 6.0 to 7.9. Both subtilisins exhibited substantial inactivation during multihour incubations in tert‐amyl alcohol and acetonitrile when enzymatic activities were also measured in these solvents; however, when the enzymes were assayed in water instead, hardly any loss of activity was detected. This surprising difference appears to stem from the partitioning of the bound water essential for catalytic activity from the enzymes into the solvents. When assayed in organic solvents, this time‐dependent stripping of water results in decay of enzymatic activity; however, when assayed in water, where the dehydrated subtilisins can undergo rehydration thereby recovering catalytic activity, little inactivation is observed. In agreement with this hypothesis, the addition of small quantities of water tert‐amyl alcohol stabilized the subtilisins in it even when enzymatic activity was measured in the nonaqueous solvent. Ester substrates (vinyl butyrate and trichloroethyl butyrate) greatly enhanced the stability of both subtilisins in organic solvents possibly because of the formation of the acyl‐enzymes.
On the enthalpy of formation of Escherichia coli K‐12 cells
Authors: Battley Edwin H. 
Published: December 2004

AbstractAn examination is made of five methods for obtaining values of the enthalpy of formation of a unit mass of living Escherichia coli K‐12 cells. The values obtained by these methods ranged from −88.95 kJ to −99.55 kJ, the gross average being 96.01 kJ, per unit carbon formula weight equivalent of living, hydrated cells. Although theoretically the growth of this organism in a microcalorimeter should provide the best value, the value obtained by this method (−88.95 kJ per UCFW equivalent) is not in close agreement with those of the other four methods, the values from which form a cluster averaging −97.8 ± 1.0 kJ (−23.4 ± 0.2 kcal)/UCFW equivalent. Calculations using this value indicate that the enthalpy change accompanying anabolism (as this is represented) is zero, or very nearly so, and that the heat of growth is that from catabolism alone.
Solubilizing water involved in protein extraction using reversed micelles
Authors: Ichikawa Sosaku , Imai Masanao , Shimizu Masaru 
Published: December 2004

AbstractThe extraction of protein using reversed micelles was investigated in relation to the amount of solubilizing water in the reversed micellar organic phase. The minimal concentration of amphiphilic molecule di‐2‐ethylhexyl sodium sulfosuccinate (C20H37O7Na) (AOT) required for 100% cytochrome c extraction was recognized. This critical AOT concentration increased with protein concentration in the aqueous phase. On this minimal AOT condition, the molar ratio of solubilizing water to extracted protein was found to be a constant of 3500 under CKCI = 1.0 × 102 mol · m−3 in this system. This ratio means the hydrophillic surroundings required for extracting one protein molecule into the micellar organic phase under the suitable pH and salt concentration for the forward extraction. In this regard, AOT molecules seemed to take the part of water solubilizing agent in the reversed micellar extraction. This role of AOT is important to extract protein under the suitable pH and salt concentration. The amount of solubilizing water in the protein‐containing system was larger than in the protein‐free system. This difference shows that the water molecules accompany the extracted protein into the reversed micellar organic phase at constant ratio 2200 under CKCI = 1.0 × 102 mol · m−3, i.e., accompanying water molecules per one extracted protein. The minimal AOT concentration increased with ionic strength. On this minimal AOT condition, the molar ratio of solubilizing water to extracted protein also increased with ionic strength, so that in higher ionic strength, more solubilizing water was required. Then more AOT was required to provide the hydrophillic surroundings for protein. The pH affected the minimal AOT concentration required for 100% protein extraction.
In vitro culture of hybridoma cells in agarose beads producing antibody secretion for two weeks
Authors: Cadic Ch. , Dupuy B. , Pianet I. , Merle M. , Margerin Ch. , Bezian J. H. 
Published: December 2004

AbstractA new process for embedding cells in agarose is described. Beads were obtained by extruding an ultralow gelling temperature agarose solution in a capillary containing a hydrophobic medium flowthrough. The toxicity of the procedure has been evaluated by monitoring the energy status of agarose‐embedded C6 glioma cells with 31P nuclear magnetic resonance (NMR). Suspension and microbead cultures of hybridoma cell line were compared. In suspension culture the number of cells and the antibody concentrations increased for 5 days before the stationary phase began, when the cultures were stopped. In agarose bead cultures, the gel provided an enormous support surface area (50 m2/ mL of gel). It was possible to seed 20‐fold more cells. The gel pressure modified the proliferative process and antibody pattern secretion. In particular, the antibodies could be harvested for two weeks.
Continuous butanol/isopropanol fermentation in down‐flow column reactor coupled with pervaporation using supported liquid membrane
Authors: Matsumura Masatoshi , Takehara Shigemasa , Kataoka Hiroshi 
Published: December 2004

AbstractContinuous butanol/isopropanol fermentation with immobilized Clostridium isopropylicum was performed in a downflow column reactor using molasses as the substrate. In order to prevent product inhibition and at the same time obtain high concentration of the products, the column reactor was coupled with a pervaporation module using a supported liquid membrane. The liquid membrane was prepared with oleyl alcohol nontoxic to the microorganism. In comparison with the continuous fermentation without product removal, the specific butanol production rate was 2 times higher. The butanol concentration in the permeate was 230 kg/m3, which was about 50 times higher than that in the culture broth. A numerical investigation suggested a further increase in the productivity by improving the module construction.
Biocatalytic synthesis of disaccharide high‐intensity sweeterner sucralose via a tetrachlororaffinose intermediate
Authors: Bennett Christopher , Dordick Jonathan S. , Hacking Andrew J. , Cheetham Peter S. J. 
Published: December 2004

AbstractA second high‐yielding bioorganic synthesis of the highintensity sweetener sucralose (4,1′,6′‐trichloro‐4,1′,6′‐trideoxygalactosucrose) is described. This procedure involves the chemical chlorination of raffinose to form a novel tetrachloroaffinose intermediate (6,4′,1″,6″‐tetrachloro‐6,4′,1″,6″‐tetradeoxygalactoraffinose; TCR) followed by the enzymic hydrolysis of the α‐1‐6 glycosidic bond of TCR to give sucralose and 6‐chlorogalactose. Commercial enzyme preparations and microorganisms were screened to select α‐galactosidases which have high catalytic activity on this compound. The most active enzyme was produced by a strain of Mortierella vinacea and had a maximum rate of 118 μmol sucralose/g dry weight cells/h, which was approximately 5% of the activity toward raffinose, and a Km of 5.8 mM toward TCR. The enzyme could be used in the form of mycelial pellets in a continuous packed bed column reactor. The reaction was also studied in a water‐immiscible hydrophilic organic solvent, such as methyl isobutyl ketone, to overcome the poor aqueous solubility of TCR and to increase volumetric productivity. Synthesis of raffinose was achieved from saturated aqueous solutions of galactose and sucrose using a selected α‐galactosidase from Aspergillus niger. When raffinose is used as a starting material for sucralose synthesis, this route has fewer steps than either the preceeding method using glucose‐6‐acetate as an intermediate or the complete chemical synthesis from sucrose. The relative merits of the two bioorganic routes and the utility of such methods to synthesize new sugars are discussed.
Simulation of L/A control in fed‐batch culture of baker's yeast
Authors: Dantigny Philippe , Lakrori Maqo 
Published: December 2004

AbstractL/A controllers have extended their use from continuous to fed‐batch fermentation where the control is applied from the start of an initial batch phase. As opposed to proportional integral derivative (PID) controllers where even a startup procedure is recommended prior to fed‐batch, the L/A controller is not upset by an early connection. It is easily retuned continuously by means of ethanol measurements and can cope with a large range of output conditions. The performance of an L/A algorithm, which uses biomass concentration as the controlled variable, is assessed through simulation. The self‐contained algorithm is relatively simple with no greater intrinsic complexity than modern PID stand alone controllers.
Use of a structured kinetic model of antibody synthesis and secretion for optimization of antibody production systems: I. Steady‐state analysis
Authors: Bibila Theodora A. , Flickinger Michael C. 
Published: December 2004

AbstractSteady‐state simulations using our previously developed structured kinetic model of antibody synthesis and secretion by hybridoma cells are used here in conjunction with factorial design analysis to identify intracellular parameters important in determining the specific antibody secretion rate and predict the dependence of this rate on cell specific growth rate. Simulation results suggest that the specific growth rate, the assembly rate of the heavy and light chains and the heavy‐ and ‐chain gene dosage can significantly affect the rate of antibody secretion. Based on these results, environmental and/or genetic manipulation approaches are proposed for maximizing the specific antibody secretion rate and the antibody volumetric productivity in large‐scale antibody production systems.
Modeling high‐biomass‐density cell recycle fermentors
Authors: Monbouquette Harold G. 
Published: December 2004

AbstractSince intrinsic models, which take into account cell volume fraction, follow from proper application of the law of conservation of mass to a multiphase system, the intrinsic modeling approach should be used whenever biomass occupies a significant volume fraction of the culture. A recent report11 offers the first comparison of intrinsic and nonintrinsic model predictions to actual experimental data gathered from a high‐density yeast recycle fermentor. Here, the analysis of Jarzebski et al.11 has been carried further to show that the improper nonintrinsic model predicts a steady‐state culture glucose concentration that differs from that given by the fundamentally correct intrinsic model by over 60% at the optimal, bleed stream flow rate. In addition, a revised formulation for an intrinsic ethanol mass balance is presented.
Effect of adsorbents on degradation of toxic organic compounds by coimmobilized systems
Authors: Siahpush Ali R. , Lin Jian‐Er , Wang Henry Y. 
Published: December 2004

AbstractThe use of coimmobilized systems for treatment of toxic organic compounds has been proposed. The proposed approach combines the use of adsorbents and laboratory identified microorganisms immobilized in a protective permeable barrier to achieve a greater degree of control over the remediation process. This study was launched to understand the effect of adsorbents and changes in adsorption on the degradation of toxic compounds by coimmobilized systems. The specific case studied involved the degradation of pentachlorophenol (PCP) by Arthrobacter (ATCC 33790) coimmobilized with powdered activated carbon within calcium alginate capsules.The design parameters studied included adsorbent content and type as well as the effect of solution pH and surfactant concentration on adsorption and biodegradation. It was found that the equilibrium adsorption behavior of PCP was strongly influenced by solution pH and surfactant concentration. A mathematical model was developed that combined the physical processes of mass transfer and adsorption with biological degradation of PCP. The model was used to predict the effect of various parameters on the degradation of PCP. Based on model predictions, the degradation of PCP. Based on model predictions, the degradation of PCP was strongly dependent on variations in adsorbent capacity and affinity for this contaminant.
Accurate pseudoanalytical solution for steady‐state biofilms
Authors: Sáez Pablo B. , Rittmann Bruce E. 
Published: December 2004

AbstractAn extremely accurate pseudoanalytical solution for the flux of substrate into a steady‐state biofilm is developed. The standard deviations between the substrate fluxes computed from the pseudoanalytical solution and the numerical solution were less than 2.6%. Additional advantages of the pseudoanalytical solution are that it has no inaccuracies around S = 1 and it is composed of single continuous functions applicable to the whole S region.
Lactose/whey utilization and ethanol production by transformed Saccharomyces cerevisiae cells
Authors: Porro Danilo , Martegani Enzo , Ranzi Bianca Maria , Alberghina Lilia 
Published: December 2004

AbstractStrains of Saccharomyces cerevisiae transformed with a multicopy expression vector bearing both the Escherichia coli β‐galactosidase gene under the control of the upstream activating sequence of the GAL1–10 genes and the GAL4 activator gene release part of β‐galactosidase in the growth medium. This release is due to cell lysis of the older mother cells; the enzyme maintains its activity in buffered growth media. Fermentation studies with transformed yeast strains showed that the release of β‐galactosidase allowed an efficient growth on buffered media containing lactose as carbon source as well as on whey‐based media. The transformed strains utilized up to 95% of the lactose and a high growth yield was obtained in rich media. High productions of ethanol were also observed in stationary phase after growth in lactose minimal media.