bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrite inhibition of denitrification by Pseudomonas fluorescens
Authors: Almeida J. S. , Júlio S. M. , Reis M. A. M. , Carrondo M. J. T. 
Published: December 2004

AbstractUsing a pure culture of Pseudomonas fluorescens as a model system nitrite inhibition of denitrification was studies. A mineral media with acetate and nitrate as sole electron donor and acceptor, respectively, was used. Results obtained in continuous stirred‐tank reactors (CSTR) operated at pH values between 6.6 and 7.8 showed that growth inhibition depended only on the nitrite undissociated fraction concentration (nitrous acid). A mathematical model to describe this dependence is put forward. The maximum nitrous acid concentration compatible with cell growth and denitrification activity was found to be 66 μg N/L. Denitrification activity was partially associated with growth, as described by the Luedeking–Piret equation. However, when the freshly inoculated reactor was operated discontinuosly, nitrite accumulation caused growth uncoupling from denitrification activity. The authors suggest that these results can be interpreted considering that (a) nitrous acid acts as a proton uncoupler; and (b) cultures continuoulsy exposed to nitrous acid prevent the uncoupling effect but not the growth inhibition. Examination of the growth dependence on nitrite concentration at pH 7.0 showed that adapted cultures (grown on CSTR) are less sensitive to nitrous acid inhibition than the ones cultivated in batch. © 1995 John Wiley & Sons, Inc.
Cultivation of cell–polymer tissue constructs in simulated microgravity
Authors: Freed L. E. , Vunjak‐Novakovic G. 
Published: December 2004

AbstractTissue‐engineered cartilage was cultivated under conditions of simulated microgravity using rotating bioreactors. Rotation randomized the effects of gravity on inoculated cells (chondrocytes) and permitted their attachment to three‐dimensional (3D) synthetic, biodegradable polymer scaffolds that were freely suspended within the vessel. After 1 week of cultivation, the cells regenerated a cartilaginous extracellular matrix (ECM) consisting of glycosaminoglycan (GAG) and collagen types I and II. Tissue constructs grown in simulated microgravity had higher GAG contents and thinner outer capsules than control constructs grown in turbulent spinner flasks. Two fluid dynamic regimes of simulated microgravity were identified, depending on the vessel rotation speed: (i) a settling regime in which the constructs were maintained in a state of continuous free‐fall close to a stationary point within the vessel and (ii) an orbiting regime in which the constructs orbited around the vessel spin axis. In the settling regime, the numerically calculated relative fluid‐construct velocity was comparable to the experimentally measured construct settling velocity (2–3 cm/s). A simple mathematical model was used in conjunction with measured construct physical properties to determine the hydrodynamic drag force and to estimate the hydrodynamic stress at the construct surface (1.5 dyn/cm2). Rotating bioreactors thus provide a powerful research tool for cultivating tissue‐engineered cartilage and studying 3D tissue morphogenesis under well‐defined fluid dynamic conditions. © 1995 John Wiley & Sons, Inc.
Mass transfer and temperature effects on substrate utilization in brewery granules
Authors: Wu May M. , Criddle Craig S. , Hickey Robert F. 
Published: December 2004

AbstractLiquid film and diffusional resistances of brewery granules during acetate, propionate, and ethanol utilization were investigated. Substrate utilization rate increased with decreased granule size. Effectiveness factors for acetate, propionate, and ethanol were calculated by comparing the maximum rates of substrate utilization of whole granules (1.8 to 3.0 mm) and fine flocs (20 to 75 μm) derived by disrupting whole granules. For acetate, propionate, and ethanol, maximum specific substrate utilization rates (km′ g/g VS · d) for the flocs, were 5.11, 6.25, and 5.49, respectively, and half‐velocity coefficients (Kg′ mM) were 0.45, 0.40, and 3.37, respectively. Calculated effectiveness factors were 0.32, 0.41, and 0.75 for acetate, propionate, and ethanol, respectively. The effect of temperature on substrate utilization was examined at 26°C, 31°C, and 37°C using acetate as sole carbon source. Utilization rates increased with temperature. Flocs were most sensitive to temperature, and whole granules were least affected. The behavior of flocs was well described by the Van't Hoff–Arrhenius equation. Effectiveness factors for acetate utilization by the granules were 0.36, 0.35, and 0.32 at 26°C, 31°C, and 37°C, respectively, indicating little effect of temperature. Based on these results, we conclude that both liquid film and diffusional resistances influenced the rate of substrate utilization in a UASB reactor with granular sludge. Temperature effects were much less important than diffusional limitations within the granules. © 1995 John Wiley & Sons, Inc.
Polysulfone affinity membranes for the treatment of amino acid mixtures
Authors: Rodemann Klaus , Staude Eberhard 
Published: December 2004

AbstractAffinity membranes for the treatment of solutions containing amino acids were obtained via lithiating polysulfone that was subsequently converted with glycidylether. From this polymer asymmetric ultrafiltration membranes were cast. The membranes were reacted with iminodiacetic acid yielding membranes fitted out with bidentate chelates. The same reaction path was applied to commercially available symmetric microfiltration membranes. The chelate‐bearing membranes were complexed with Cu, Ni, and Zn ions. For the experiments with amino acids only the Cu‐complexed membranes were used. The complexation constants for histidine and tryptophan for six different membranes were determined. Because of the affinity of these two amino acids for the complexed Cu ions, they could easily be separated from solutions containing amino acids such as alanine, glycine, and valine. Also, concentrating very dilute amino acid solutions was carried out successfully. © 1995 John Wiley & Sons, Inc.
Process optimization and modeling of trichlorophenol degradation by Phanerochaete chrysosporium
Authors: Pal Nirupam , Lewandowski Gordon , Armenante Piero M. 
Published: December 2004

AbstractThe biodegradation of 2,4,6‐trichlorophenol and 2,4,5‐trichlorophenol by the white rot fungus Phanerochaete chrysosporium was studied in batch and continuous reactor systems. Experiments were conducted in shake flasks as well as in packed‐bed reactors in which the fungus was immobilized. The degradation rates in the packed‐bed reactors were found to be two orders of magnitude greater than those obtained in the shake flasks in which the fungus was just suspended. The degradation rate was found to be influenced by the concentrations of the carbon and nitrogen sources, pH, and fluid shear stress. Optimal ranges of these parameters to maximize biodegradation were determined. A mathematical model was developed in which the degradation process was assumed to consist of two sequential reaction steps, the first catalyzed by an extracellular enzyme system and the second requiring the presence of the mycelium. The deactivation of the extracellular enzyme system was also accounted for in the model. The Michaelis–Menten and the enzyme deactivation parameters were determined independently. Good agreement between the experimental data and the results produced by the regression was found. © 1995 John Wiley & Sons, Inc.
Effects of temperature and cycloheximide on secretion of cloned invertase from recombinant Saccharomyces cerevisiae
Authors: Marten Mark R. , Chung Bong‐Hwan , Seo Jin‐Ho 
Published: December 2004

AbstractThe effects of temperature on the kinetics and efficiency of secretion of cloned invertase were investigated in a recombinant yeast system. This system consisted of the baker's yeast Saccharomyces cerevisiae (SEY2102) transformed with the 2μ‐based plasmid pBR58 which contains the entire SUC2 gene including the promoter, signal sequence, and structural gene. The recombinant yeast produces the naturally secreted yeast enzyme invertase. In transition experiments done at temperatures ranging from 25° to 45°C, the maximum invertase level and secretion rate exhibited maxima of 5.5 U/mL · OD and 4.6 U/mL · OD per hour, respectively, at 35°C. Experiments involving the use of cycloheximide showed that it took approximately 15 min for secreted invertase to move through the secretion pathway, which held 0.4 U/mL · OD of specific activity. © 1995 John Wiley & Sons, Inc.
Protein recovery from cell debris using rotary and tangential crossflow microfiltration
Authors: Parnham Charles S. , Davis Robert H. 
Published: December 2004

AbstractProtein recovery from a bacterial lysate was accomplished using microfiltration membranes in a flat crossflow filter and in a cylindrical rotary filter. Severe membrane fouling yielded relatively low long‐term permeate flux values of 10−4–10−3 cm/s (where I cm/s = 3.6 × 104 L/m2 – h). The permeate flux was found to be nearly independent of transmembrane pressure and to increase with increasing shear rate and decreasing solids concentration. The flux increased with shear to approximately the one‐third power or greater for the flat filter and the one‐half power or greater for the rotary filter; the stronger dependence for the rotary filter is thought to result from Taylor vortices enhancing the back transport of debris carried to the membrane surface by the permeate flow. The average protein transmission or sieving coefficient was measured at approximately 0.6, but considerable scatter in the transmission data was observed. The largest sieving coefficients were obtained for dilute suspensions at high shear rate. The rotary filter provided higher fluxes than did the flat filter for dilute suspensions, but not for concentrated suspensions. © 1995 John Wiley & Sons, Inc.
Characterization of a pH‐inducible promoter system for high‐level expression of recombinant proteins in Escherichia coli
Authors: Chou Chih‐Hsiung , Aristidou Aristos A. , Meng Shi‐Yuan , Bennett George N. , San Ka‐Yiu 
Published: December 2004

AbstractA pH‐inducible promoter system was characterized and its potential applicability in recombinant protein production was evaluated using a plasmid construct, pSM552‐545C−, in which the promoter and activator coding sequences of the cad operon were inserted into the upstream region of a lacZ′ reporter gene. Graded gene expression levels with respect to culture pH between 8.0 and 5.5 were observed and the induction range can be as high as 200‐fold. The effects of several cultivation parameters, including pH, temperature, induction cell density, and inoculum size, were systematically examined. The practical application of this expression system to high level production of recombinant proteins was successfully demonstrated using a rich medium, superbroth. An extremely high recombinant protein productivity at a value of approximately 1.4 g/L with a specific expression level as high as 35% of total cellular protein can be obtained in a simple batch cultivation. The behavior of this expression system was further investigated using chemostat cultures. An uncommon relationship between the volumetric or specific recombinant protein activity and the dilution rate, with a maximal activity at a dilution rate of approximately 0.4 h−1was observed. © 1995 John Wiley & Sons, Inc.
Affinity purification of proteins using ligands derived from peptide libraries
Authors: Huang Ping Y. , Carbonell Ruben G. 
Published: December 2004

AbstractPeptide libraries can be used to identify ligands that bind specifically to a desired protein. These peptides may have significant advantages as specific ligands for affinity chromatography separations. This article describes the use of one of such peptide, Try‐Asn‐Phe‐Glu‐Val‐Leu, as a ligand for the purification of S‐protein using affinity chromatography. General strategies for peptide immobilization are discussed and the conditions for peptide immobilization to Emphaze™ gel are optimized. The effects of peptide orientation and peptide densities on protein binding are studied. Results indicate that the peptide affinity is not affected by the orientation of the peptide during immobilization, but association constants can be reduced by one order of magnitude when compared with the values in solution.With increased peptide density, the protein binding capacity of the gel increases, but both the percentage of peptide utilization and apparent binding constant between immobilized peptide and S‐protein decrease. S‐protein is separated from a mixture with BSA via affinity chromatography using specific elution with the peptide in solution.Finally, direct purification of S‐protein from an enzymatic digestion mixture of ribonuclease A is demonstrated.© 1995 John Wiley & Sons, Inc
High‐rate continuous biodegradation of concentrated chlorinated aliphatics by a durable enrichment of methanogenic origin under carrier‐dependent conditions
Authors: Boucquey J.‐B. , Renard P. , Amerlynck P. , Filho P. Modesto , Agathos S. N. , Naveau H. , Nyns E.‐J. 
Published: December 2004

AbstractThe simultaneous biodegradation of toxic compounds in mixtures is a major current concern. To bioremediate a toxic mixture, we designed a strategy combining an ad‐sorbent carrier with an ecological and nutritional system which allowed work close to heavily polluted conditions in nature. Starting from a methanogenic community, we developed a microbial consortium acclimated to a mixture of about 30 chlorinated aliphatics in a fixed‐film stationary‐bed bioreactor. Prior to the establishment of a durable period of dechlorination, an interval of progressive dechlorination of the toxic mixture was observed during which the excess of the toxic compounds was stored on the carrier. The latter, consisting of activated carbon in a polyurethane foam, allowed us to work at concentrations far above the solubility of the toxic compounds (apparent concentrations of about 10 g/L). The complete disappearance of hexachloroethane as well as its lower homologues, penta‐, tetra‐, and trichloroethane, present in the toxic mixture, was observed. Additionally, octachlorocyclopentene, carbon tetrachloride, trichloro‐ethylene, tetrachloroethylene, and hexachloro‐1,3‐butadiene also completely disappeared. For the four latter compounds, from mass balances in the bioreactor, degradation rates around 10 μmol/L per day were determined with total dechlorination. The enrichment culture thus developed exhibited high degradation performances similar to those reported in the literature for pure or enriched anaerobic microbial cultures in contact with a single toxic compound. The results demonstrate the possibility of concurrent high‐rate degradation of several highly chlorinated toxic compounds, under conditions approximating field situations.© 1995 John Wiley & Sons, Inc
Mathematical modeling and analysis of glucose and glutamine utilization and regulation in cultures of continuous mammalian cells
Authors: Zeng A.‐P. , Deckwer W.‐D. 
Published: December 2004

AbstractA number of factors have been shown to affect the metabolism of glucose and glutamine in mammalian cells and their mechanisms have been partially elucidated. Despite these efforts, a quantitative knowledge of the significance of these factors, the regulation of glucose and glutamine utilization, and particularly the interactions of these two nutrients is still lacking. Controversies exist in the literature. To clarify some of these controversies, mathematical models are proposed in this work which enable to separate and identify the effects of individual factors. Experimental data from five cell lines obtained in batch, fed‐batch, and continuous cultures, both under steady‐state and transient conditions, were used to verify the model formulations. The resulting kinetic models successfully describe all these cultures. According to the models, the specific consumption rate of glucose (QGlc) of continuous animal cells under normal culture conditions can be expressed as a sum of three parts: a part owing to cell growth; a part owing to glucose excess; and a part owing to glutamine regulation. The specific consumption rate of glutamine (qGlc7) can be expressed as a sum of only two parts: a part owing to cell growth; and a part owing to glutamine excess. Using the kinetic models the interaction and regulation of glucose and glutamine utilizations are quantitatively analyzed. The results indicate that, whereas qGlc is affected by glutamine, qGln appears to be not or less significantly affected by glucose. It is also shown that the relative utilizations of glucose and glutamine by anabolism and catabolism are mainly affected by the residual concentrations of the respective compounds and are less sensitive to growth rate and the nature of growth limitation.© 1995 John Wiley & Sons, Inc
Optimization of step gradient separations: Consideration of nonlinear adsorption
Authors: Gallant Stuart R. , Kundu Amitava , Cramer Steven M. 
Published: December 2004

AbstractNonlinear adsorption plays an important role in determining the chromatographic behavior of proteins in preparative ion‐exchange chromatography. In this article, the steric mass action (SMA) isotherm is used in conjunction with a mass transport model to describe nonlinear cation‐exchange chromatography. Excellent agreement is observed between simulated and experimental step gradient separations of the proteins α‐chymotryp‐sinogen A, cytochrome C, and lysozyme. A systematic method of selecting the optimum step gradient program for a given separation problem is presented and employed to study optimization of step gradient chromatography under conditions of high mass loading. This article includes consideration of the effects of the adsorption properties of the feed stream, the feed stream concentration, protein solubility, and otherconstraints on the optimum separation conditions.© John Wiley & Sons, Inc.
Description of two‐metal biosorption equilibria by Langmuir‐type models
Authors: Chong K. H. , Volesky B. 
Published: December 2004

AbstractA biosorbent prepared from Ascophyllum nodosum seaweed biomass, FCAN2, was examined for its sorption capacity. Equilibrium batch sorption studies were performed using two‐matal systems containing either (Cu + Zn), (Cu + Cd), or (Zn + Cd). In the evaluation of the two‐metal sorption system performance, simple isotherm curves had to be replaced by three‐dimensional sorption isotherm surfaces. In order to describe the isotherm surfaces mathematically, three Langmuir‐type models were evaluated. The apparent one‐parameter Langmuir constant (b) was used to quantify FCAN2 “affinity” for one metal in the presence of another one. The uptake of Zn decreased drastically when Cu or Cd were present. The uptake of Cd wasmuch more sensitive to the presence of Cu than to that of Zn. The presence of Cd and Zn alter the “affinity” of FCAN2 for Cu the least at high Cu equilibrium concentrations. The mathematical model of the two‐metal sorption system enabled quantitative estimation of one‐metal (bio)sorption inhibition due to the influence of a second metal. © 1995 John Wiley & Sons Inc.
Purification of an L‐asparaginase—atrial natriuretic peptide fusion protein expressed in Escherichia coli
Authors: Ma Nien‐Tung , Wang Yun‐Fang , Roe Bruce A. , Harrison Roger G. 
Published: December 2004

AbstractA novel fusion protein designed to facilitate protein purification was expressed in Escherichia coli and purified separately by two different chromatography methods. L‐Asparaginase from Erwinia chrysanthemi is fused to the N‐terminus of a model peptide, α‐human atrial natriuretic peptide (α‐hANP). L‐Asparaginase was chosen because of its selective affinity for L‐asparagine and because of its unusually high isoelectric point(8.6). A gene construction without the L‐asparaginase native signal sequence caused expression at a level of 8% of total cell protein, while gene construction with the native signal sequence resulted in over five time less expression. The hybrid protein expressed without the signal sequence was purified from clarified cell lysate byeither L‐asparagine affinity chromatography or cation exchange chromatography. After digestion of the fusion protein with factor Xa protease, a peptide with a molecular weight corresponding to the theoretical molecular weight of α‐hANP was observed by coupled HPLC/mass spectrometry. © 1995 John Wiley & Sons Inc.
Extraction of lysozyme and ribonuclease‐a using reverse micelles: Limits to protein solubilization
Authors: Lye G. J. , Asenjo J. A. , Pyle D. L. 
Published: December 2004

AbstractExperiments are reported here on the equilibrium partitioning of lysozyme and ribonuclease‐a between aqueous and reversed micellar phases comprised of an anionic surfactant, sodium di‐2‐ethylhexyl sulfosuccinate (AOT), in isooctane. A distinct maximum, [P]rm,max was found for the quantity of a given protein that can be solubilized in the reverse micelle phase by the phase‐transfer method. This upper limit depended upon the size of the protein, the surfactant concentration, and the aqueous phase ionic strength, and was determined by complex formation between protein and surfactant molecules to form an insoluble interfacial precipitate at high values of [P]rm. In this work, it was found to be possible to dissociate the protein–surfactant complex and recover the precipitated protein. The kinetics of protein–surfactant complex formation depended upon the nature and concentration of the solubilized protein and on the surfactant concentration. Calculations of micellar occupancy and the relative surface areas of protein molecules and surfactant head‐groups suggested that it was the exposure of the solubilized protein to the bulk organic solvent which promoted protein–surfactant complex formation as [P]rm → [P]rm,max. In the light of the experimental results and calculations described above, a mechanistic model is proposed to account for the observed phenomena. This is based upon the competing effects of increasing the solubilized protein concentration and the corresponding increase in the rate of protein‐surfactant complex formation. The dynamic nature of the reverse micelles is inherent in the model, explaining the formation of the interfacial precipitate with time and its dependence on the internal phase volume of the micellar phase. Experiments on the co‐partitioning of water and measurement ofthe AOT concentration in both phases verified the loss of protein, water, and surfactant from the organic phase at high values of [P]rm. © 1995 John Wiley & Sons Inc.
Oxygen transfer and culture characteristics of self‐immobilized Solanum aviculare aggregates
Authors: Ananta Ita , Subroto M. Ahkam , Doran Pauline M. 
Published: December 2004

AbstractOxygen transfer characteristics of self‐immobilized Solanum aviculare cells were measured using aggregates 3.0 to 12.5 mm in diameter. Apparent specific oxygen uptake rates in the absence of external boundary layers varied from 5.9 × 10−11 to 8.5 × 10−7 kg kg−1 s−1 dry weight, but did not decline continuously with increasing particle size. The effective diffusivity of oxygen in deactivated aggregates increased with particle diameter, varying from 5.0 × 10−11 to 1.0 × 10−9 m2 s−1 or between 2% and 40% of the molecular diffusivity in water at the same temperature. Gas spaces detected in the larger aggregates were confined to the central core and were not distributed throughout the tissue to facilitate oxygen transfer. Oxygen consumption rates in the absence of diffusional limitations were estimated using the relationship between the observable Thiele modulus and effectiveness factor for zero‐order reaction. The calculated results indicated severe oxygen limitations in the aggregates, but were inconsistent with the observation that relatively large S. aviculare aggregates contained a high fraction of viable cells and were capable ofactive growth and steroidal alkaloid synthesis. This work suggests that oxygen delivery is facilitated in living plant cell aggregates by mechanisms which depend on metabolic activity and which do not function in deactivated cells. © 1995 John Wiley & Sons Inc.