bluuebunny/crossref_metadata_2025 huggingface dataset:
High stability to irreversible inactivation at elevated temperatures of enzymes covalently modified by hydrophilic reagents: α‐Chymotrypsin
Authors: Mozhaev Vadim V. , Melik‐Nubarov Nickolay S. , Levitsky Vladislav Y. U. , Siksnis Virginius A. , Martinek Karel
Published: December 2004

Based on the idea that proteins can be stabilized by a decrease in the thermodynamically unfavorable contact of the hydrophobic surface clusters with water, α‐chymotrypsin (CT) was acylated with carboxylic acid anhydrides or re‐ductively alkylated with aliphatic aldehydes. Modification of CT with hydrophilic reagents leads to 100‐1000‐fold increase in stability against the irreversible thermoinactivation. The correlation holds: the greater the hydrophilization increment brought about by the modification, the higher is the protein thermostability. After some limiting value, however, a further increase in hydrophilicity does not change thermostability.

It follows from the dependence of the thermoinactivation rate constants on temperature that for hydrophilized CT there is the conformational transition at 55‐65°C into an unfolded state in which inactivation is much slower than that of the low‐temperature conformation. The thermodynamic analysis and fluorescent spectral data confirm that the slow inactivation of hydrophilized CT at high temperatures proceeds via a chemical mechanism rather than Incorrect refolding operative for both the native and low‐temperature form of the modified enzyme. Hence, the hydrophilization stabilizes the unfolded high‐temperature conformation by eliminating the incorrect refolding. © 1992 John Wiley & Sons, Inc.
Enhanced β‐galactosidase production by high cell‐density culture of recombinant Bacillus subtilis with glucose concentration control
Authors: Park Yong Soo , Kai Kenichi , Iijima Shinji , Kobayashi Takeshi
Published: December 2004

Cell concentration, recombinant protein (β‐galactosidase) level, and the specific enzyme expression level were increased from 19 to 184 g/L, 18.3 to 129 U/mL, and 3.2 to 5.7 U/mg protein, respectively, in fed‐batch culture of recombinant Bacillus subtilis when glucose concentration was controlled at 1 g/L as compared with those of conventional fed‐batch culture. Glucose concentration of the culture broth was monitored by an automatic on‐line glucose analyzer and controlled with a moving identification combined with optimal control (MICOC) strategy. When glucose concentrations were controlled at 10, 1, and 0.2 g/L, accumulated propionic acid concentrations and specific enzyme activities were 18.5, 4.4, and 0.6 g/L and 2.9, 5.7, and 7.1 U/mg protein, respectively. The addition of various concentrations of sodium propionate to the growth medium in batch cultures resulted in a drastic decrease in the growth rate with respect to propionate concentration. The propionic acid was shown to be responsible for cell growth inhibition and enzyme activity reduction in fed‐batch culture. © 1992 John Wiley & Sons, Inc.
Cultivation of Methylosinus trichosporium OB3b: III. Production of particulate methane monooxygenase in continuous culture
Authors: Shah Nilesh N. , Park Sunghoon , Taylor Robert T. , Droege Michael W.
Published: December 2004

Continous culture experiments with the obligatory methanotroph, Methylosinus trichosporium OB3b, were conducted to study the whole‐cell methane monooxygenase (MMO) and nitrogenase activities in a nitrate minimal salts medium under oxygen‐limited conditions with methane as the carbone source. The important variables investigated were the feed medium concentrations of copper and nitrate, CO2 addition, the agitation speed, and the dilution rate. M. trichosporium OB3b required quantitative amounts of copper (2.6 × 10−4 g Cu/g dry cell Wt) for the exclusive production of particulate MMo during continous culture growth. When the feed medium nitrate concentration was varied in the range of 5‐50 mM, the whole‐cell specific pMMO activity exhibited a maximum at 40 mM. The elimination of external CO2 gassing decreased pMMO activity by more than 30%. The steady‐state cell density increased continuously over a 300‐700 rpm range of agitation speed, whereas, the pMMO activity became maximal at 400 rpm. Also, the pMMO activity increased with the dilution rate up to 0.06 h−1 and remained constant thereafter. Maximal continuous pMMO productivity was, thus, achieved in Higgin's medium containing 10 μM Cu, 80 μM Fe, and 40 mM nitrate with an agitation speed of 500 rpm and a dilution rate of 0.06 h−1. Nitrogenase activity, on the other hand, increased over a feed medium copper concentration of 2‐15 μM, falling sharply at 20 μM, and it exhibited a minimum at 20 mM when the feed medium nitrate concentration was varied. © 1992 John Wiley & Sons, Inc.
Influence of total and oxygen partial pressure on growth and metabolism of Methylomonas clara
Authors: Liefke E. , Onken U.
Published: December 2004

The effect of total and oxygen partial pressure on metabolic activities of Methylomonas clara has been investigated in batch and continuous cultivation experiments using a pressurizable airlift loop reactor. At Oxygen partial pressures of more than 1000 mbar growth of M. Clara is retarded and completely inhibited at 1200 mbr. However, after several hours of incubation at elevated oxygen partial pressures, biomass formation is nearly doubled in subsquent continuous operation, Cells pretreated with oxygen are characterized by a change of cytochrome content; they excret carboxylic acids into the medium. The results indicate that, by sparging an aerobic culture intermittently wich pure oxygen, formation of biomass might be enbanced. © 1992 John Wiley & Sons, Inc.
Improvement of shikonin productivity in Lithospermum erythrorhizon cell culture by alternating carbon and nitrogen feeding strategy
Authors: Srinivasan Venkatesh , Ryu Dewey D. Y.
Published: December 2004

Stationary phase cell suspension cultures of Agrobacterium tumefaciens transformed Lithospermum erythrorhizon respond to additions of sucrose‐rich (C‐rich) medium with a 2–3‐fold increase in the accumulation of shikonin derivatives and a 3–3.5‐fold increase in the accumulation of soluble phenolics while showing a modest (10–30%) increase in cell concentration. Conversely, the addition of nitrate‐rich (N‐rich) medium resulted in 25–35% increase in biomass concentration but only 2–9% increase in shikonin production and ∼ 3% increase in the yield of soluble phenolics. Repeated additions of C‐rich medium resulted in only a modest (less than 10%) improvement in shikonin production over the levels obtained after the first application. No obvious correlation could be discerned between intracellular ATP levels or protein synthesis patterns and the pattern of shikonin accumulation following the addition of C‐rich medium, suggesting that the precursor diversion mechanism is not generally applicable in our cell line. It was found that alternating feeding of N‐rich and C‐rich media could be used as an effective strategy for enhancing the productivity of plant secondary metabolite. © 1993 John Wiley & Sons, Inc.
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

An 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

The 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

A 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

Aspergillus 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

The 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

Improvement 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

Poly(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

Cartilage 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

The 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

Using 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

High 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

Biotransformations 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

Recycling 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

A 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

In 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.
Enhancement of antibody production by growth factor addition in perfusion and hollow‐fiber culture systems
Authors: Omasa Takeshi , Kobayashi Masaki , Nishikawa Toshio , Shioya Suteaki , Suga Ken‐ichi , Uemura Syo‐ichi , Kitani Yasuo , Imamura Yoshio
Published: December 2004

The effects of the high‐molecular‐weight growth factors, transferrin and bovine serum albumin (BSA), on antibody production were analyzed quantitatively in continuous hollow‐fiber cultivation over a period of 60 days. Transferrin enhanced cell growth but had no significant effect on the specific antibody production rate, whereas BSA significantly enhanced antibody production. The antibody production rate was increased 4‐ and 14‐fold respectively by feeding BSA at 2 and 5 g L−1 into the EC side of the system (the side connected to the cell‐containing outer part of the hollow‐fiber unit) compared with the production achieved without BSA. Addition of 5 g L1 BSA into the IC side of the system (the side connected to the inner part of the hollow‐fiber unit) resulted in a 2.5‐fold increase in the antibody production rate. The effect of BSA was also analyzed using the perfusion culture system with a separation unit. When fresh medium containing either 2 or 5 g L−1 BSA was fed into the reactor, both the specific growth rate and specific death rate increased, while the specific antibody production rate was increased 2‐ and 25‐fold, respectively, by feeding BSA at these two concentrations compared with no addition. Comparing the two systems, the increase in the antibody production rate achieved with the hollow‐fiber system was threefold greater than that in the perfusion culture system with the same concentration of BSA feeding. © 1995 John Wiley & Sons, Inc.
Enhancement of monoclonal antibody production by immobilized hybridoma cell culture with hyperosmolar medium
Authors: Park Sung Young , Lee Gyun Min
Published: December 2004

To determine the effect of hyperosmotic stress on the monoclonal antibody (MAb) production by calcium‐alginate‐immobilized S3H5/γ2bA2 hybridoma cells, the osmolalities of medium in the MAb production stage were varied through the addition of NaCI. The specific MAb productivity (qMAb) of immobilized cells exposed to abrupt hyperosmotic stress (398 mOsm/kg) was increased by 55% when compared with that of immobilized cells in the control culture (286 mOsm/kg). Furthermore, this enhancement of qMAb was not transient. Abrupt increase in osmolality, however, inhibited cell growth, resulting in no increase in volumetric MAb productivity (rMAb). On the other hand, gradual increase in osmolality allowed further cell growth while maintaining the enhanced qMAb immobilized cells. The qMAb immobilized cells at 395 mOsm/kg was 0.661 ± 0.019 μg/106 cells/h, which is almost identical to that of immobilized cells exposed to abrupt osmotic stress. Accordingly, the rMAb was increased by ca. 40% when compared with that in the control immobilized cell culture. This enhancement in iMAb of immobilized S3H5/γ2bA2 hybridoma cells by applying gradual osmotic stress suggests the potential of using hyperosmolar medium in other perfusion culture systems for improved MAb production. © 1995 John Wiley & Sons, Inc.
Comprehensive modeling of methanogenic biofilms in fluidized bed systems: Mass transfer limitations and multisubstrate aspects
Authors: Buffière Pierre , Steyer Jean‐Philippe , Fonade Christian , Moletta René
Published: December 2004

A cognitive model for anaerobic digestion in fluidized bed reactors is developed. The general pathway of the process is divided into five main reactions performed by different bacterial groups. Molecular diffusion of each substrate involved in the reaction scheme is described. Effectiveness factor calculations are performed in steady state for each bacterial group taken into account in the process. The case of a single substrate removal is discussed, and optimal biofilm sizes are found. Sequential substrate removal is investigated, and different kinetic regimes are characterized. The influence of biofilm size and primary substrate removal is discussed in the case of standard concentrations in the liquid phase. This study shows that, according to the theoretical model the limiting step of the process may be different and depends in a large way on mass transfer effects. Finally, importance of biofilm size is compared for acidogenic and methano‐genic steps: each reaction is found to be optimized for different biofilm thicknesses. This result may be of interest for design purposes and further dynamic modeling. Concluding remarks concerning the validation of the model are made, and a comparison to experimental data from the literature is presented. © 1995 John Wiley & Sons, Inc.
Purification of industrial αamylase by reversed micellar extraction
Authors: Chang Qing‐Long , Chen Jia‐Yong
Published: December 2004

The purification of industrial α‐amylase by liquid‐liquid extraction with Aliquat 336 reversed micellar solution as the extractant was studied. Seven kinds of Aliquat 336 reversed micellar solution, formed by using seven kinds of straight chain alkyl alcohols as cosolvent, have been utilized to extract industrial a‐amylase. It was found that these seven kinds of reversed micellar solution can all achieve a high protein transfer efficiency in the forward extraction process. After a full forward and backward extraction cycle, however, only the reversed micelles with n‐butanol as the cosolvent was found to be able to maintain the activity of α‐amylase in the stripping solution. By using the reversed micelles of Aliquat 336/isooctane/1% (v/v) n‐butanol to perform a full extraction cycle, it was found that 85% of the total activity of α‐amylase in the industrial a‐amylase could be recovered at the end of an extraction cycle and the specific activity of α‐amylase could be concentrated about 1.5‐fold; meanwhile, most of the neutral protease in the industrial a‐amylase could be removed. The separation factor of α‐amylase to neutral protease at the end of an extraction cycle can reach about 10. © 1995 John Wiley & Sons, Inc.
Druckabfall und Wärmeübergang eines Wärmeaustauschers neuartiger Konstruktion
Authors: Grassmann P. , Hildesheimer H.
Published: December 2004

Es wird ein Wärmeaustauscher beschrieben, bei dem der Gasstrom durch mehrere Siebplatten mit gegeneinander versetzten Löchern dem Dampfstrom entgegenströmt. Die drei untersuchten Bauarten zeigten Gütegrade zwischen 0,75 und 1,25 und sehr niedrige Gewichte, bezogen auf die Austauschfläche, so daß die Anwendung in Luftverflüssigungsanlagen kurze Anfahrzeiten ermöglicht.
Präparative Chromatographie
Authors: Fritz H. , Bauer A.
Published: December 2004

Es wird eine große unterteilte Chromatographiersäule beschrieben, mit der an einer Füllung aus Cellulose‐Pulver, z. B. 70 g eines Gemisches der vorgereinigten Alkaloidchloride aus Calebassencuraro, in einem Durchlauf in die Hauptfraktionen aufgetrennt werden können.
Pyrolytic CVD of poly(organosiloxane) thin films
Authors: Kwan Michael C. , Gleason Karen K.
Published: December 2004

Communication: Silicone films have a wide range of applications. All efforts to date to deposit them have concentrated on PECVD, but ths technique has the problem of introducing defects into the layers as a result of UV irradiation and ion bombardment. A pyrolytic process has te possibility of depositing layers with a lower density of dangling bonds. This paper presents rate and with a similar structure to that of poly(dimethylsiloxane).
Effects of porcelain application procedures on two noble alloys
Authors: Bagby M. , Marshall S. J. , Marshall G. W.
Published: December 2004

Distortion of ceramometal restorations during porcelain application is often attributed to mismatch of thermal expansion coefficients. Little attention has been paid to treatment the metal receives after casting. Oxide formation, lattice parameter changes, and macroscopic distortion were studied for flat specimens of two ceramometal alloys, a high Pd alloy and a high Au alloy. SnO2 and In2O3 formed on the surface of the high Au alloy after the oxidation firing, while SnO2 and CuGa2O4 formed on the high Pd alloy. Lattice parameter changes reflected the loss of base metal elements in the formation of surface oxides. The edges of specimens distorted toward the ground side. Such distortion can be explained by the induction of residual stress in the metal surface during grinding and subsequent surface stress annealing accompanied with subsurface elastic recovery during firings. Oxide formation was not related to specimen distortion. This study suggests a relationship between surface preparation and specimen distortion during porcelain application procedures.
A nondenaturing solid phase pharmaceutical carrier comprised of surface‐modified nanocrystalline materials
Authors: Kossovsky Nir , Bunshah Rointan F. , Gelman Andrew , Sponsler Edward , Umarjee Dheerendra M. , Suh Tae‐Gyo , Prakash Shiva , Doerr Hans J. , Deshpandey Chandra V.
Published: December 2004

Numerous carrier systems have been developed for the controlled delivery of biologically active molecules such as drugs and diagnostic agents. The biophysical interactions between the biologically active molecules and their carriers, however, may denature the former and lead to reduced biological activity. In this study, a model nondenaturing carrier comprised of a nanocrystalline (10−7 m) tin oxide core and a surface‐charge‐reducing organic bonding layer (GF292) was synthesized. A subsequently bound protein (human transferrin) showed significant retained conformation by immunoelectron microscopy. In the synthesis of targeted drug systems and vaccines, nanocrystalline cores treated with appropriate surface‐modifying agents may be suitable carriers.
Relationship of the diameter and tensile strength of nylon sutures to the USP specification and the effect of preconditioning
Authors: Whitley J. Q. , Prewitt M. J. , Kusy R. P.
Published: December 2004

Nylon monofilament sutures were tested in a straight pull as well as a conventional knot pull tensile test. In each test, sutures were evaluated following storage under prevailing atmospheric conditions or saturation in whole human blood. Blood saturation decreased the ultimate tensile strength by as much as 20%. The present investigation of sutures that were stored under prevailing atmospheric conditions substantiated the proposal previously made for polypropylene monofilaments‐that 60% of the ultimate tensile strength could be established as a fundamental USP criterion for Class I monofilament sutures.
Über die Berufsausbildung von Korrosionsfachleuten, Galvanotechnikern und Werkstofftechnikern in Deutschland
Authors: Machu Willi
Published: December 2004

Während die Ausbildung von Galvanotechnikern in Deutschland in Fachschulen ausreicht, ist der derzeitige Lehrplan an den Universitäten und Technischen Hochschulen zur Heranziehung von Wissenschaftlern und Technikern für Forschung und Entwicklung für das Werkstoff‐ und Korrosionsgebiet nicht geeignet. Es werden daher Vorschläge zur Schaffung eigener Lehrkanzeln oder Fakultäten für diese Gebiete vorgelegt und deren Lehrfächer und Aufbau zur Diskussion gestellt.
Entwicklung und besondere Vorteile der zylindrischen Mehrlagenhohlkörper für hohe Innendrücke
Authors: Class I.
Published: December 2004

Stahl‐Hohlkörper zur Aufnahme hoher Innendrücke werden in verschiedenen Industriezweigen für Flüssigkeiten, und Dämpfe benötigt. Bei den Hohlkörpern der Chemie sind Spitzenanforderungen zu erfüllen in bezug auf die Höhe der Drücke und Temperaturen und Größe der Körper, Beherrschung der Einwirkung von angreifenden chemischen Agenzien, sowie elastische Handhabung von Heizung und Kühlung. Der vorliegende Aufsatz schildert den Entwicklungsgang von einteiligen Hohlkörpern, die z. B. auf schweren Schmiedepressen hergestellt werden können, zur Mehrteilbauweise, insbesondere zu den aus mehreren Lagen geschichteten Hohlkörpern, wobei der Wickelkörper überragende Bedeutung gewann. Die Probleme der Festigkeit und Sicherheit werden vollkommen beherrscht; darüber hinaus bietet die Mehrschichtbauweise durch Wahl verschiedener Werkstoffe für Innenschicht und äußere Lagen eine einfache und wirtschaftliche Möglichkeit des Korrosionsschutzes.
Die Reaktionen zwischen CuO und Fe bzw. Fe3O4 im festen Zustand und ihre Beeinflussung durch O2 und H2O‐Dampf
Authors: Wickert Kurt , Wiehr Hartmuth
Published: December 2004

Die Umsetzung von CuO mit Fe ist nach der Methode der Erhitzungskurven schon ab 193° C nachweisbar. Diese Reaktion wird durch O2 angeregt, so daß sie dann bei niedrigeren Temperaturen beginnt und abläuft als bei Abwesenheit von Sauerstoff. O2 und H2O‐Dampf sind in der Lage, die Reaktion plötzlich ablaufen zu lassen, so daß hohe Temperaturen entstehen, während sie bei Abwesenheit dieser beiden Gase unter gleichen Reaktionsbedingungen langsam verläuft. Ähnlich wie mit Fe reagiert CuO auch mit Fe3O4. Bei dieser Reaktion tritt aber kein Maximum in der Erhitzungskurve auf.

In Bezug auf die Praxis im Dampfbetrieb ist die Entstehung von metallischem Kupfer von Bedeutung und die Tatsache, daß hohe örtliche Temperaturen auftreten können. Die Entstehung von Fe2O3 durch die Umsetzung zwischen CuO und Fe3O4 ist für die Beurteilung von Korrosionen ebenfalls von Bedeutung.
Systematische Versuche zur Prüfung der korrosionsverhindernden Wirkung von VPI auf eine Reihe von gebräuchlichen Metallen
Authors: Paul Werner
Published: December 2004

Der Korrosionsschutz mittels „Vapor Phase Inhibitor”︁ findet in der Industrie immer stärkere Beachtung. Bislang beschränkte sich die Anwendung dieses Verfahrens hauptsächlich auf Stahlerzeugnisse, bei denen in jedem Fall vorzügliche Ergebnisse zu erwarten sind. In der vorliegenden Arbeit wurden die Verhaltensweisen auch anderer viel verwendeter Metalle und Metallegierungen gegen VPI systematisch untersucht. Es wurde nachgewiesen, daß die korrodierende Wirkung atmosphärischer Einflüsse auch bei Eisen‐ und Nichteisenmetallen verhindert werden kann. Den einschlägigen Industrie‐zweigen stehen damit exakte Unterlagen zur Verfügung, so daß nun auch dort die vielfachen Vorteile des VPI‐Verfahrens nutzbringend angewendet werden können.
Glasfaserverstärkte Kunststoffe in der chemischen Industrie
Authors: Jaray F. F.
Published: December 2004

Es wird ein ausführlicher Überblick über Aufbaustoffe, Herstellung und Eigenschaften der glasfaserverstärkten Kunststoffe gegeben, die in den verschiedenen Zweigen der chemischen Technik in Form von Halbzeug und Formkörpern zunehmende Verwendung finden und sich durch besondere mechanische, thermische und chemische Eigenschaften auszeichnen. Neben den üblichen und bekannten Herstellungsverfahren erfahren auch die modernen Spezialverfahren (Bewickeln der Form mit gerichtetem Glas‐Halbzeug unter mechanischer Spannung, Herstellung von Halbzeug unter Vorreckung der Fasern während der Aushärtung des Harzes, Verwendung spezieller Kunstharze, die beim Abkühlen nur in geringem Maße schrumpfen, Verwendung weicher deformierbarer Zwischenschichten) eine ebenso ausführliche wie offene Darstellung. Für die in USA auf dem Gebiete der glasfaserverstärkten Kunststoffe erzielten Erfolge sprechen zahlreiche im Bild wiedergegebene kleinere und größere Anlagen.
Verlegen und Schweißen von Kunststoffrohren
Authors: Pischke Hans
Published: December 2004

Schweißbar sind nur Rohre aus thermoplastischen Kunststoffen. Vor allem Polyvinylchlorid‐hart und Polyäthylen sind als Rohrwerkstoffe in großem Umfang in der chemischen Industrie, aber auch in der Frischwasserversorgung und für Wasserabfuhr eingesetzt. Die Verarbeitung und Verlegung dieser Rohrmaterialien wird besprochen, verschiedene Verbindungsverfahren werden kritisch betrachtet, und es werden neuere, jedoch bereits bewährte Verfahren aufgezeigt.
Polyäthylen‐Plastikrohre. Lieferarten, Dimensionierung, Eigenschaften, Verlegung und Verbindung
Authors: Köhler W.
Published: December 2004

Rohre aus Weich‐ und Hartpolyäthylen (Supralen, weich und Supralen, hart) finden infolge ihrer guten allgemeinen und spezifischen Eigenschaften, insbesondere ihres ausgezeichneten korrosionschemischen Verhaltens, zunehmende Verwendung in Anlagen zur Förderung aggressiver Flüssigkeiten und Gase. Im Hinblick darauf gibt der vorliegende Fortschrittsbericht einen zusammenfassenden und zeitgemäßen Überblick über Lieferarten und Dimensionierung, über das physikalische (mechanische, thermische, elektrische, hydraulische, akustische und optische Eigenschaften) und korrosionschemische Verhalten sowie über die Verlegung und Verbindung von Polyäthylen‐Plastikrohren.
Das Vanalverfahren – Ein neuartiger Korrosionsschutz
Authors: Staerker A.
Published: December 2004

Es wird ein neues Verfahren beschrieben, durch das die Oberflächen feuerfester Baustoffe vor vorzeitiger Korrosion bei hohen Temperaturen geschützt werden. Die Wirkung beruht auf dem Gesetz der Oberflächenspannung, das hierfür erstmalig angewandt wird. Durch entsprechend ausgerichtete Schutzschichten wird das Eindringen von Gasen und Schlacken verhindert. An Hand von Beispielen as der Praxis wird der technische und wirtschaftliche Vorteil dieses Verfahrens besonders bei Siliciumcarbid erläutert.
Hochkorrosionsbeständige Legierungen in Kohlenwertstoffanlagen
Authors: Wahrburg Günter
Published: December 2004

Ein neues Druckverfahren für die Entschwefelung von Ammoniakgas wurde bei der Harpener Bergbau A.G., Dortmund, eingeführt. Bei der Anlage handelt es sich im wesentlichen um eine Druckkolonne von 600 mm Durchmesser und 12 m Höhe sowie einige Nebenapparaturen.

Die anfänglich für den Bau verwendeten herkömmlichen Werkstoffe, u. a. auch austenitische rost‐ und säurebeständige Stäble, genügten den Anforderungen nicht. Sie wurden mitunter bereits nach wenigen Monaten durch Korrosion zerstört. Es wurde deshalb die Eignung der Hastelloy‐Legierungen überprüft. Korrosionsversuche unter Betriebsbedingungen (in [%] 20 NH3, 12 H2S, 6 CO2, max. 2 HCN; 160 bis 180° C; 12 atü) ergaben bei Hastelloy Alloy C (mit [%] 60 Ni, 16 Mo, 16 Cr, 4 W) einen Korrosionsverlust von 0,0014 g/m2·h.

Die Anlage wurde daraufhin in Hastelloy C erstellt. Die T.Ü.V.‐Prüfung bestätigte die Werte der Soll‐Analyse und ermittelte bei der mechanischen Prüfung folgende Werte: Streckgrenze 48,3 kg/mm2, Zugfestigkeit 83,5 kg/mm2, Dehnung 56%. Die Druckprüfung mit 15,6 kg/cm2 Wasserdruck sowie die Röntgenprüfung der Schweißnähte ergab keine Beanstandungen.

Die Anlage ist seit Oktober 1955 in Betrieb und arbeitet seither ohne Anstände. Das gute Verhalten des Werkstoffes Hastelloy veranlaßte das vorgenannte Unternehmen, inzwischen weitere Anlagen hieraus herstellen zu lassen.