bluuebunny/crossref_metadata_2025_split huggingface dataset:
An integrated metabolic modeling approach to describe the energy efficiency of Escherichia coli fermentations under oxygen‐limited conditions: Cellular energetics, carbon flux, and acetate production
Authors: Ko Yun‐Fei , Bentley William E. , Weigand William A. 
Published: December 2004

AbstractAn integrated metabolic model for the production of acetate by growing Escherichia coli on glucose under aerobic conditions is presented. The model is based on parameters which are easily determined by experiments. Forming the basis for this integrated metabolic model are the 12 principal precursor metabolites for biosynthetic pathways, the Embden–Meyerhof–Parnas pathway, the pentose phosphate cycle, the tricarboxylic acid cycle and the anapleurotic reactions, the Crabtree effect, the Pasteur effect, and the details of bacterial respiration. The result can be used to explain phenomena often observed in industrial fermentations, i.e., increased acetate production which follows from high glucose uptake rate, a low oxygen concentration, a high specific growth rate, or a combination of these conditions. © 1993 John Wiley & Sons, Inc.
Review: Tissue engineering: Reconstitution of human hematopoiesis ex vivo
Authors: Koller Manfred R. , Palsson Bernhard O. 
Published: December 2004

AbstractThe reconstruction of functioning human tissues ex vivo is becoming an important part of biotechnology. There are compelling scientific, clinical, and biotechnological reasons for fully or partially reconstituting human tissues such as skin, bone marrow, and liver ex vivo. In particular, bone marrow is a tissue of much importance, and there are significant societal and health benefits derived from a successfully constructed ex vivo hematopoietic system. In this article, we review the current status of this effort. The topics covered include the current understanding of the biology of human hematopoiesis, the motivation for reconstructing it ex vivo, the current state of ex vivo human hematopoietic cultures, the development of important metrics to judge culture performance, and an approach based on in vivo mimetics to accomplish this goal. We discuss some applications of functional ex vivo hematopoietic cultures and the biological and engineering challenges that face research in this area. © 1993 John Wiley & Sons, Inc.
Hydrodynamics and mixing in a multiple air‐lift loop reactor
Authors: Bakker W. A. M. , van Can H. J. L. , Tramper J. , de Gooijer C. D. 
Published: December 2004

AbstractA new bioreactor, in which a series of air‐lift reactors with an internal loop is incorporated into one vessel, is introduced. With this multiple air‐lift loop reactor (MAL) and approximation of an aerated plug‐flow fermentor is strived for. Mixing, liquid velocity, and gas holdup were measured as a function of the gas flow rate in this new internal‐loop reactor geometry. As a reference, hydrodynamics were also investigated in a conventional internal‐loop reactor. A model description of the hydrodynamics in the second compartment of the MAL is given. This model is based on a two‐phase, drift‐flux model and a friction coefficient. Frictional losses were independent of the reactor bottom geometry, and were observed to increase with the gas flow rate as a result of the presence of stationary gas bubbles in the downcomer. The hydrodynamics and mixing of the second MAL compartment were comparable with those of conventional internal‐loop reactors. © 1993 John Wiley & Sons, Inc.
Correlation of Aspergillus niger broth rheological properties with biomass concentration and the shape of mycelial aggregates
Authors: Olsvik E. , Tucker K. G. , Thomas C. R. , Kristiansen B. 
Published: December 2004

AbstractAspergillus niger was grown in a 7‐L chemostat at biomass levels of 7 to 9 gL−1; dilution rates of 0.03, 0.05, 0.075, and 0.009 h−1; and dissolved oxygen tensions of 7%, 12%, and 40% of air saturation. Broth rheological measurements were made on‐line, while off‐line image analysis was used to measure mycelial morphology, including characterization of mycelial aggregates (clumps). Under all conditions, more than 87% of the hyphase were in clumps, the shape of which determined the rheological characteristics of the broth. In particular, the power law consistency index could be correlated with the biomass concentration and the roughness factor of the clumps, which describes their hairiness. A decrease in specific growth rate decreased roughness, possibly due to changes in the amount of clump breakup. However, decreases of roughness with increasing dissolved oxygen tension might rather imply some effect on hyphal–hyphal interactions within the clumps. © 1993 John Wiley & Sons, Inc.
The effect of the dilution rate on CHO cell physiology and recombinant interferon‐γ production in glucose‐limited chemostat culture
Authors: Hayter Paul M. , Curling Elisabeth M. A. , Gould Malcolm L. , Baines Anthony J. , Jenkins Nigel , Salmon Ian , Strange Philip G. , Bull Alan T. 
Published: December 2004

AbstractThe physiology of a recombinant Chinese hamster ovary cell line in glucose‐limited chemostat culture was studied over a range of dilution rates (D = 0.008 to 0.20 h−1). The specific growth rate (μ) deviated from D at low dilution rates due to an increased specific death rate. Extrapolation of these data suggested a minimum specific growth rate of 0.011 h−1 (μmax = 0.025 h−1) The metabolism at each steady state was characterized by determining the metabolic quotients for glucose, lactate, ammonia, amino acids, and interferon‐γ (IFN‐γ). The specific rate of glucose uptake increased linearly with μ, and the saturation constant for glucose (Ks) was calculated to be 59.6 μM. There was a linear increase in the rate of lactate production with a higher yield of lactate from glucose at high growth rates. The decline in the rate of production of lactate, alanine, and serine at low growth rate was consistent with the limitation of the glycolytic pathway by glucose. The specific rate of IFN‐γ production increased with μ in a manner indicative of a growth‐related product. Despite changes in the IFN‐γ production rate and cell physiology, the pattern of IFN‐γ glycosylation was similar at all except the lowest growth rates where there was increased production of nonglycosylated IFN‐γ. © 1993 John Wiley & Sons, Inc.
Effect of solvent on enantioselective esterification of naproxen by lipase with trimethylsilyl methanol
Authors: Tsai Shau‐Wei , Wei Hwa‐Jou 
Published: December 2004

AbstractImprovement of stereoselective resolution of racemic Naproxen, 2‐(6‐methoxy‐2‐naphthyl)propionic acid, was attempted with esterifcation reaction by Candida cylindracea lipase. By carefully selecting the organic medium, a 72‐time enhancement of yield of the desired S‐ester was achieved. The optimal reaction temperature was approximately 53°C, and an alcohol concentration between 20 mM and 40 mM in an 80% (v/v) isooctane and 20% (v/v) toluene mixture was found. © 1994 John Wiley & Sons, Inc.
Poly(ethylene oxide)‐grafted thermoplastic membranes for use as cellular hybrid bio‐artificial organs in the central nervous system
Authors: Shoichet Molly S. , Winn Shelley R. , Gentile Frank T. , Athavale Sushama , Milton Harris J. 
Published: December 2004

AbstractPoly(acrylonitrile‐co‐vinyl chloride) (PAN/VC) anisotropic membranes were chemically modified with poly(ethylene oxide) (PEO) (5000 and 20,000 g/mol) by one of two aqueous reactions: (a) acid hydrolysis of the nitrile group to a carboxylic acid with which amine‐terminated PEO (PEO‐NH2) reacted or (b) base reduction of the nitrile group to an amine with which PEO‐succinimide (PEO‐SC) reacted. Approximately 1.3% of the bulk material was modified with PEO‐NH2 whereas 1.8 to 3.5% was modified with PEO‐SC as determined by proton nuclear magnetic resonance (1H NMR) and attenuated total reflectance Fourier transform infrared (ATR FTIR) spectra. Approximately 50 to 75% less bovine serum albumin (BSA) adsorbed to PEO‐grafted single skin fibers than to unmodified PAN/VC. Transport properties of modified and unmodified fibers were compared by passive diffusion, convective nominal molecular weight cutoff, and hydraulic permeability. Neither hydraulic permeability nor nominal molecular weight cutoff of BSA changed appreciably after surface modification with PEO indicating that pore structure was not adversely affected by the chemistry involved in grafting poly(ethylene oxide). However, in the absence of any membrane conditioning, the apparent diffusion of α‐chymotrypsinogen (24,000 g/mol) was enhanced in PEO‐grafted PAN/VC fibers possibly as a result of reduced sorption of the permeating protein. In vivo biocompatibility in the brain tissue of rats was judged by histological assessment of the host's cellular response to fibers implanted for 30 days; biocompatibility of both PAN/VC and PAN/VC‐g‐PEO was satisfactory but improved slightly with PEO grafting. © 1994 John Wiley & Sons, Inc.
Composition of cell‐polymer cartilage implants
Authors: Freed L. E. , Marquis J. C. , Langer R. , Vunjak‐Novakovic G. , Emmanual J. 
Published: December 2004

AbstractCartilage implants for potential in vivo use for joint repair or reconstructive surgery can be created in vitro by growing chondrocytes on biodegradable polymer scaffolds. Implants 1 cm in diameter by 0.176 cm thick were made using isolated calf chondrocytes and polyglucolic acid (PGA). By 6 weeks, the total amount of glycosaminoglycan (GAG) and collagen (types I and II) increased to 46% of the implant dry weight; there was a corresponding decrease in the mass of PGA. Implant biochemical and histological compositions depended on initial cell density, scaffold thickness, and the methods of cell seeding and implant culture. Implants seeded at higher initial cell densities reached higher GAG contents (total and per cell), presumably due to cooperative cell‐to‐cell interactions. Thicker implants had lower GAG and collagen contents due to diffusional limitations.Implants that were seeded and cultured under mixed conditions grew to be thicker and more spatially uniform with respect to the distribution of cells, matrix, and remaining polymer than those seeded and/or cultured statically. Implants from mixed cultures had a 20‐40‐μm thick superficial zone of flat cells and collagen oriented parallel to the surface and a deep zone with perpendicular columns of cells surrounded by GAG Mixing during cell seeding and culture resulted in a more even cell distribution ad enhanced nutrient diffusion which could be related to a more favorable biomechanical environment for chondrogenesis. Cartilage with appropriate for and function for in vivo implantation ca thus be created by selectively stimulating the growth and differentiated function of chondrocytes (i.e., GAG and collagen synthesis) through optimization of the in vitro culture environment. © 1994 John Wiley & Sons, Inc.
Engineering organ perfusion protocols: NMR analysis of hepatocyte isolation from perfused rat liver
Authors: Foy Brent D. , Toner Mehmet , Tompkins Ronald G. , Yarmush Martin L. 
Published: December 2004

AbstractThe development and use of an extracorporeal liver support device depends upon the isolation of a large number of viable, functioning hepatocytes from whole or partial livers. Current practice, however, produces nonoptimal yields, given that a large percentage of hepatocytes initially present are not successfully isolated. The normal hepatocyte isolation protocol consists of sequential perfusion with calcium chelating and collagenase buffers, and then separation of viable hepatocytes from non‐viable and nonparenchymal cells, usually on the basis of cell density. In order to improve understanding regarding the metabolic and perfusion state of the liver during this perfusion protocol, ATP, pH, and tissue perfusion were evaluated using nuclear magnetic resonance (NMR). Perfusion with calcium chelating buffer was found to have minimal effect on the metabolic and perfusion parameters, whereas subsequent perfusion with collagenase buffer produced large declines in ATP, pH, and homogeneity of perfusion within 3 min. Perfusion with calcium‐chelating buffer alone, or perfusion with calcium chelating buffer followed by a short period of ischemia to mimic the perfusion disruption of collagenase, did not produce the same decline in metabolic parameters. This NMR data suggested that enhancing the early perfusion and penetration of collagenase or prolonging the nontoxic calcium‐chelation step may improve the yield and/or functionality of isolated cells. Therefore, several altered perfusion protocols were evaluated in terms of yield of viable parenchymal hepatocytes and hepatocyte albumin production. Although increasing the perfusion flow rate and initial perfusion with inactive (cold) collagenase did not produce significant improvements when compared with the control protocol (control cell yield 226 ± 42 × 106 viable hepatocytes for 10‐ to 14‐week‐old female Lewis rat), prolonging and enhancing the calcium‐chelating perfusion step or increasing the collagenase concentration did yield a significantly great number of viable parenchymal hepatocytes (393 ± 44 and 328 ± 39 × 106 viable hepatocytes, respectively) with no change in albumin production per seeded viable cell. © 1994 John Wiley & Sons, Inc.
Importance of solute partitioning in biphasic oxidation of benzyl alcohol by free and immobilized whole cells of pichia pastoris
Authors: Kawakami Koei , Nakahara Takehiko 
Published: December 2004

AbstractUsing free and immobilized whole cells of Pichia pastoris, the biocatalytic oxidation of benzyl alcohol was investigated in different two‐phase systems. This reaction was strongly influenced by both the substrate and product inhibitions, and the production rate of benzaldehyde in the aqueous system became maximum at the initial substrate concentration of ca. 29 g/L with the aldehyde formation less than 4 to 5 g/L even after a longer reaction period. The reaction rates in the two‐liquid phase systems were predominantly determined by the partitioning behaviors of the substrate and product between the two phases rather than by enzyme deactivation by the organic solvents. In the two‐liquid phase systems, consequently, the organic solvent acted as a reservior to reduce these inhibitory effects, and it was essential to select the organic solvent providing the optimal partitioning of the substrate into the aqueous phase as well as the preferential extraction of the product into the organic phase. The whole cells immobilized in a mixed matrix composed of silicone polymer [>50% (v/v)] and Ca alginate gel (<50%) worked well in the xylene and decane media, providing comparable activities with the free cells. The production rate of aldehyde was also influenced by the solute partitioning into the hydrophilic alginate phase where the cells existed. © 1994 John Wiley & Sons, Inc.
High cell density fermentation of recombinant Vibrio cholerae for the production of B subunit of Escherichia coli enterotoxin
Authors: Panda Amulya K. , Ghorpade Anuja , Mukhopadhyay Asok , Talwar G. P. , Garg L. C. 
Published: December 2004

AbstractHigh cell density fermentation studies were performed to produce the B subunit of Escherichia coli heat‐labile enterotoxin (LTB) from a Vibrio cholerae culture that carries a recombinant plasmid with an ampicillin resistance gene, tac promoter, and the gene encoding LTB. Upon induction with isopropyl‐β‐D‐thiogalactopyranoside (IPTG) the culture secreted the protein into the extracellular milieu. Fed‐batch fermentation with stepwise addition of a total of 5 mM of IPTG during the active growth phase of the organism resulted in the production of 400 mg/L of LTB in 9 h and a cell optical density (OD) of 24. The LTB was purified to homogeneity with 70% recovery from the fermentation broth and was found to be chemically and biologically identical to the native protein by N‐terminal amino acid sequencing and receptor binding assay. © 1995 John Wiley & Sons, Inc.
Enzyme catalyzed biotransformations in aqueous two‐phase systems with precipitated substrate and/or product
Authors: Kasche V. , Galunsky B. 
Published: December 2004

AbstractBiotransformations catalyzed by free and immobilized enzymes have been carried out in aqueous suspensions with up to 25% (w/w) precipitated substrate or product. For the kinetically controlled synthesis of N‐Acetyl‐Tyr–Arg–NH2 with up to 0.8 M insoluble activated substrate N‐Acetyl–TyrOEt catalyzed by α‐chymotrypsin (EC3.4.21.1) the dipeptide yield was found to be >90%. This and the space‐time yields were higher than those observed for one‐phase aqueous systems and much higher than in systems where the insoluble substrate had been solubilized by addition of organic solvents. In the equilibrium controlled hydrolysis of 0.4 M D‐phenylglycine‐amide catalyzed by immobilized penicillin amidase (EC 3.5.1.11) the product precipitates. The enzyme immobilized in the support with the smallest pores could be reused without reduction in the rate due to precipitation in the pores. This decreases the number of immobilized enzyme molecules that can be used as biocatalysts. The latter was observed for supports with larger pores as the solubility decreases with increasing particle size. These results demonstrate that biotransformations with insoluble substrates or products using free or immobilized enzymes can be easily carried out in aqueous two‐phase systems, without organic solvents, provided that the pore sizes of the supports are sufficiently small and that the rate of mass transfer from the precipitated substrate is large. The latter increases with decreasing particle size. © 1995 John Wiley & Sons, Inc.
Evaluation of cellulase recycling strategies for the hydrolysis of lignocellulosic substrates
Authors: Lee Dora , Yu Alex H. C. , Saddler John N. 
Published: December 2004

AbstractRecycling of cellulases should lower the overall cost of lignocellulosiic bioconversion processes. In this study, three recycling strategies were evaluated to determine their efficiencies over five successive rounds of hydrolysis. The effect of lignin on recycling was examined by comparing water‐washed, steam‐exploded birch (WB; 32% lignin) and WB which had been further extracted with alkali and peroxide (PB; 4% lignin). When the cellulases were recovered from the residual substrates after partial hydrolysis of both substrates, the recovered cellulase activity toward the mixture of fresh and residual substrates decreased after each recycling step. When the cellulases in the supernatants were also recycled, up to 20% more activity could be recovered. In both of these cases, the recovered activities did not correspond to the activities expected from the amount of cellulase protein recovered during recycling. The best recovery was obtained when the cellulases were recovered from both the residue and the supernatant after complete hydrolysis of the PB substrate. In this case, all of the originally added cellulase activity could be recovered for four consecutive hydrolysis rounds. However, when the same recycling strategy was carried out using the WB substrate, the recovered cellulase activity declined quickly with each recycling round. In all three of the recycling strategies, lower cellulase activities were recovered from the substrates with higher lignin contents. © 1995 John Wiley & Sons, Inc.
A model of the binding, entry, uncoating, and RNA synthesis of Semliki Forest virus in baby hamster kidney (BHK‐21) cells
Authors: Dee Kennie U. , Hammer Daniel A. , Shuler Michael L. 
Published: December 2004

AbstractA quantitative understanding of viral trafficking would be useful in treating viral‐mediated diseases, designing protocols for viral gene therapy, and optimizing heterologous protein production. In this article, a model for the trafficking of Semliki Forest virus and its RNA synthesis in baby hamster kidney (BHK‐21) cells is presented. This model includes the various steps leading to infection such as attachment, endocytosis, and viral fusion in the endosome. The model estimates a mean fusion time of 4 to 6 min for the wild‐type virus, and 38 min forFus‐1, an SFV mutant which requires a lower pH for fusion. These mean fusion times are consistent with the time‐scale of endosomal acidification, suggesting viruses fuse almost instantaneously with the endosomal membrane as soon as the pH of the endosome drops below the pH threshold of the virus. Infection is most likely controlled at the level of viral uncoating, as shown by the close agreement between the efficiency of uncoating and the experimentally determined fraction of viruses that is infectious. The viral RNA synthesized per cell is best described by assuming that it depends on the number of uncoated viruses prior to the onset of replication according to a saturation‐type expression. A Poisson distribution is used to determine the distribution of uncoated viruses among the cells. Because attachment is the rate‐limiting step in the uncoating of the virus, increasing the attachment rate can lead to enhanced RNA synthesis and, hence, new virion production. Such an increase in the attachment rate may be obtained by lowering the medium pH or the addition of a polycation. © 1995 John Wiley & Sons, Inc.
Adaptive on‐line model for aerobic Saccharomyces cerevisiae fermentation
Authors: von Schalien Randolf , Fagervik Kaj , Saxén Björn , Ringbom Knut , Rydström Mikael 
Published: December 2004

AbstractIn order to study and control fermentation processes, indirect on‐tine measurements and mathematical models can be used. In this article we present a mathematical on‐line model for fermentation processes. The model is based on atom and partial mass balances as well as on equations describing the acid‐base system. The model is brought into an adaptive form by including transport equations for mass transfer and unstructured expressions for the fermentation kinetics. The state of the process, i.e., the concentrations of biomass, substrate, and products, can be estimated on‐line using the balance part of the model completed with measurement equations for the input and output flows of the process. Adaptivity is realized by means of on‐line estimation of parameters in the transport and kinetic expressions using recursive regression analysis. These expressions can thus be used in the model as valid equations enabling prediction of the process. This makes model‐based automation of the process and testing of the validity of the measurement variables possible. The model and the on‐line principles are applied to a 3.5‐L laboratory tormentor in which Saccharomyces cerevisiae is cultivated. The experimental results show that the model‐based estimation of the state and the predictions of the process correlate closely with high‐performance liquid chromatography (HPLC) analyses. © 1995 John Wiley & Sons, Inc.