bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization in integrated biochemical systems
Authors: Voit Eberhard O. 
Published: December 2004

AbstractAs of yet, steady‐state optimization in biochemical systems has been limited to a few studies in which networks of fluxes were optimized. These networks of fluxes are represented by linear (stoichiometric) equations that are used as constraints in a linear program, and a flux or a sum of weighted fluxes is used as the objective function. In contrast to networks of fluxes, systems of metabolic processes have not been optimized in a comparable manner. The primary reason is that these types of integrated biochemical systems are full of synergisms, antagonisms, and regulatory mechanisms that can only be captured appropriately with nonlinear models. These models are mathematically complex and difficult to analyze. In most cases it is not even possible to compute, let alone optimize, steady‐state solutions analytically. Rare exceptions are S‐system representations. These are nonlinear and able to represent virtually all types of dynamic behaviors, but their steady states are characterized by linear equations that can be evaluated both analytically and numerically. The steady‐state equations are expressed in terms of the logarithms of the original variables, and because a function and its logarithms of the original variables, and because a function and its logarithm assume their maxima for the same argument, yields or fluxes can be optimized with linear programs expressed in terms of the logarithms of the original variables. © 1992 John Wiley & Sons, Inc.
Influence of mass transfer limitations on determination of the half saturation constant for hydrogen uptake in a mixed‐culture CH4‐producing enrichment
Authors: Giraldo‐Gomez Eugenio , Goodwin Steve , Switzenbaum Michael S. 
Published: December 2004

AbstractThere is strong evidence in the literature supporting the existence of significant mass transfer limitations on the kinetics of exogenous H2 consumption by methanogens. The half saturation constant for H 2 uptake by a mixed‐culture, CH4 producing enrichment was measured using an experimental protocol that avoided internal mass transfer limitations. The value obtained was two orders of magnitude smaller than any other previously reported. A mathematical model for acetogenic syntrophic associations was developed to check the capacity of H2 as electron transporter between syntrophic partners. It was found that H2 diffusion could account for the rate of transport of electrons between the syntrophic microorganisms and that formate is not a necessary intermediate. The possibility that formate may be an intermediate in this system was not ruled out. A Monod‐type kinetic equation was modified to include the observed H2 threshold effect. This modified equation was used to predict the CH4‐production rate in a batch‐fed digester. The results show that the external and internal H2 pools are kinetically coupled. © 1992 John Wiley & Sons, Inc.
Cell inactivation in the presence of sparging and mechanical agitation
Authors: Yang Jeng‐Dar , Wang Nam Sun 
Published: December 2004

AbstractMicrobial cells are more readily rendered nonviable by the combined action of air sparging and mechanical agitation than by either action along. A. bubble breakup/coalescence model that incorporates the cell–bubble encounter rate, bubble breakup rate, and death probability is proposed to describe cell inactivation in the presence of bubbles maintained through the joint action of agitation and air, which is continually fed into the impeller stream region via passive vortex entrainment from the surface above or via active sparging from below. Experimental results obtained from a fragile algal (Ochromonas malhamensis) culture are consistent with the model prediction. In particular, the specific cell death rate is linearly related to the specific bubble interfacial surface area. It is shown that cells exhibit sparging‐sensitive characteristics when agitation is mild, but become sensitive to surface vortexing when agitation turns vigorous enough to introduce air entrainment. Experimental data obtained from different stirrer sizes are in good agreement with the model © 1992 John Wiley & Sons, Inc.
Direct and homogeneous immunoassay for IgG analyses
Authors: Huang Ping Yu , Lee Cheng S. , Heath Carole , Banik Gautam 
Published: December 2004

AbstractA concept involving the use of antibody conjugated with reporter molecules for direct sensing of subtle changes in the local electrostatic environment of an antigen–antibody complex due to the antigen binding is presented. The proposed direct sensing mechanism is studied using the protein A–immunoglobulin G (IgG) complex as the model system. The change in the local electrostatic potential and pH around the protein A–IgG complex is observed by measuring the fluorescence intensity of fluorescein molecules conjugated with protein A before and after the introduction of IgG. Factors affecting the efficiency of our direct sensing mechanism including the conjugation ratio of fluorescein per protein A molecule, Solution conditions, and the amount of protein A–fluorescein conjugate used in the experiment are investigated. The IgG2A concentrations in the cell supernatants are analyzed by using our direct sensing method and then compared with the results obtained from enzyme–linked immunosorbent assay (ELISA). The comparisons between our homogeneous assay and heterogeneous ELISA in the analysis time, analysis procedures, cost, and sensitivity are reported and discussed. © 1992 John Wiley & Sons, Inc.
Determination of equilibrium and individual rate constants for subtilisin‐catalyzed transesterification in anhydrous environments
Authors: Chatterjee Sudipta , Russell Alan J. 
Published: December 2004

AbstractWe report here the first determinations of individual rate constants and equilibrium constants for enzymatic reactions in essentially anhydrous organic solvents. Using the added nucleophile method we have measured the effect of changing solvent on the binding and catalytic steps for subtilisin‐catalyzed transesterification of N‐protected amino acid esters. The detailed information generated indicates that once the substrate has bound to the enzyme, the catalytic machinery can work at rates equivalent to those in water. The decreased overall rates for subtilisin suspended in anhydrous solvents are merely the result of extremely high values for Ks, in most cases, coupled with low concentrations of nucleophile (∼1.0M in organic solvents, and 55M in water). The method described, which is generally applicable, and straightforward experimentally, will, we believe, enable a clearer understanding of how changing solvent can predictably affect the activity and specificity of the enzyme. © 1992 John Wiley & Sons, Inc.
Utilization of the tricarboxylic acid cycle, a reactor design criterion for the microaerobic production of 2,3‐butanediol
Authors: Zeng An‐Ping , Deckwer Wolf‐Dieter 
Published: December 2004

AbstractA new parameter, the relative utilization of tricarboxylic acid (TCA) cycle β, is introduced to quantitatively account for the involvement of fermentation pathways and TCA cycle in the utilization of oxygen under oxygen‐limiting (microaerobic) conditions. With the facultative anaerobe Enterobacter aerogenes, which produces 2,3‐butanediol, a method is proposed to calculate β from measurement of metabolites and exhaust gas. In continuous culture β was found to be small under oxygen limitation, indicating that the fermentation pathways were preferred over the TCA cycle and oxygen was almost entirely consumed through oxidation of reduced nicotinamide adenine dinucleotide (NADH2) released by fermentation under these conditions. The increase of β at high oxygen supply revealed a saturation of oxygen utilization through fermentation pathways. It could be concluded that, for the optimal performance of a microaerobic culture, oxygen uptake rate must be kept at such a level that as much NADH2 as possible from fermentation pathways is oxidized by oxygen, and at the same time the utilization of TCA cycle is kept at a minimum. As the dynamics of the microaerobic culture can be fast, a significant effect of reactor hydrodynamics, i.e., mixing, on the overall performance can be expected. This was confirmed experimentally, and the parameter β proved to be a useful reactor design criterium for the microaerobic cultivation. © 1992 John Wiley & Sons, Inc.
Production of xylitol from D‐xylose by candida tropicalis: Optimization of production rate
Authors: Horitsu Hiroyuki , Yahashi Yuuichi , Takamizawa Kazuhiro , Kawai Keiichi , Suzuki Tohru , Watanabe Noriyasu 
Published: December 2004

AbstractThe effect of culture conditions on xylitol production rate was investigated using Candida tropicalis IFO 0618. From the variance analysis of xylitol production rate, it was found that initial yeast extract concentration was highly significant (99%), while the interaction between D‐xylose concentration and aeration rate was significant (95%). These results show the importance of initial yeast extract concentration and of the balance between D‐xylose concentration and aeration in the production of xylitol. It was also clearly shown that C. tropicalis needed more yeast extract concentration for efficient xylitol production than for its growth. In order to enhance xylitol production rate, culture conditions were optimized by the Box–Wilson method. In this respect, initial D‐xylose concentration, yeast extract concentration, and KLa were chosen as the independent factors in 23‐factorial experimental design. As the result of experiments, a maximum xylitol production rate of 2.67 g/L · h was obtained when initial D‐xylose concentration and yeast extract concentration were 172.0 and 21.0 g/L, respectively, and KLa was 451.50 h−1 by 90% oxygen gas. © 1992 John Wiley & Sons, Inc.
Biodesulfurization of water‐soluble coal‐derived material by Rhodococcus rhodochrous IGTS8
Authors: Kilbane John J. , Jackowski Kathleen 
Published: December 2004

AbstractRhodococcus rhodochrous IGTS8 was previously isolated because of its ability to use coal as its sole source of sulfur for growth. Subsequent growth studies have revealed that IGTS8 is capable of using a variety of organosulfur compounds as sources of sulfur but not carbon. In this article, the ability of IGTS8 to selectively remove organic sulfur from water‐soluble coal‐derived material is investigated. The microbial removal of organic sulfur from coal requires microorganisms capable of cleaving carbon‐sulfur bonds and the accessibility of these bonds to microorganisms. The use of water‐soluble coal‐derived material effectively overcomes the problem of accessibility and allows the ability of microorganisms to cleave carbon‐sulfur bonds present in coal‐derived material to be assessed directly. Three coals, two coal solubilization procedures, and two methods of biodesulfurization were examined. The results of these experiments reveal that the microbial removal of significant amounts of organic sulfur from water‐soluble coal‐derived material with treatment times as brief as 24 h is possible. Moreover, the carbon content and calorific value of biotreated products are largely unaffected. Biotreatment does result, however, in an increased hydrogen and nitrogen content and a decreased oxygen content of the coal‐derived material. The aqueous supernatant obtained from biodesulfurization experiments does not contain sulfate, sulfite, or other forms of soluble sulfur at increased concentrations in comparison with control samples. Sulfur removed from water‐soluble coal‐derived material appears to be incorporated into biomass. © 1992 John Wiley & Sons, Inc.
Effect of changes in the pH and carbon dioxide evolution rate on the measured respiratory quotient of fermentations
Authors: Royce Patrick N. 
Published: December 2004

AbstractThe total concentration of dissolved carbon dioxide in fermentation broths is one to two orders of magnitude greater than that of oxygen for pH > 6.5. The rate of change in this total concentration can be sufficiently large to produce a discrepancy between the carbon dioxide transfer rate (CTR) across the gas–liquid interface, available from gas analyses, and the carbon dioxide evolution rate (CER) of biomass in the fermentor. The CER is the variable of most interest to fermentation technologists but cannot be measured directly. The CTR is commonly used to yield the measured respiratory quotient (called here the TQ, or transfer quotient). Evaluation of the real underlying respiratory quotient (RQ), however, requiures the unmeasureable CER. Equations defining the problem are presented and are found to accurately predict the discrepancy between the TQ and the RQ in fed‐batch fermentations of Escherichia coli. During the exponential growth phase, the TQ is less than the RQ. A changing pH can cause the TQ to be bigger or smaller than the RQ, while pH fluctuations associated with on–off pH controller action make the CTR and hence the TQ noisy. The RQ is estimated on‐line during an E. coli fermentation and is shown to be constant during the fermentation, even though the TQ varies greatly. © 1992 John Wiley & Sons, Inc.
Protein immobilization to alumina supports: I. Characterization of alumina‐organophosphate ligand interactions and use in the attachment of papain
Authors: Hyndman David , Flynn T. Geoffrey , Lever Gordon , Burrell Robert 
Published: December 2004

AbstractThe chemical adsorption of organic phosphate compounds to alumina has been used to create surface linkers for protein immobilization. A number of particulate alumina supports were screened for their physical properties and ability to bind organic phosphate compounds. Two aluminas, termed C1 and CPC, were selected based on their suitability for subsequent testing as protein immobilization supports. Papain was successfully immobilized to these supports when derivatized with phosphate compounds containing free terminal carboxyl groups. Protein binding was enhanced when support carboxyl groups were activated with 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide. The level of papain immobilization was dependent upon the length of the linker used and the mass of protein exposed to the support. © 1992 John Wiley & Sons, Inc.
Packed bed bioreactor with porous ceramic beads for animal cell culture
Authors: Park Seujeung , Stephanopoulos Gregory 
Published: December 2004

AbstractA packed bed bioreactor was investigated as means for the cultivation of mammalian cells. The packed bed is comprised of porous ceramic particles with pores sufficiently large for cell immobilization as well as for intraparticle convective flow. In this way, the transport of limiting nutrients such as oxygen can be significantly enhanced, allowing maintenance of cell viability and productivity in an environment protective of adverse shear effects. The extent of intraparticle convective medium flow was experimentally quantified relative to the reactor operating conditions, and was found to be the dominant mechanism of nutrient transport to cells immobilized in the particle interior. An approximate linear relationship was obtained between overall reactor productivity and the extent of intraparticle convection. As the latter can be controlled at the single‐particle level through total flow rate control, this relationship is a useful scale‐up tool for the design of bioreactors. The high cell densities and the high volumetric productivities achieved by using small lab‐scale reactors underline the potential of this simple bioreactor configuration for large‐scale cell culture applications. © 1993 John Wiley & Sons, Inc.
Intracellular pH based controlled cultivation of yeast cells: I. Measurement methodology
Authors: Sureshkumar G. K. , Mutharasan R. 
Published: December 2004

AbstractA method has been developed to continuously measure the intracellular pH (pHi) of cells cultivated in a bioreactor in an on‐line fashion over extend time periods. The methods is attractive in its simplicity and involves the use of a fluorescent pHi indicator 9‐aminoacridine (9A A) which is a week base. An expression has been derived to calculate changes in pHi from measured 9AA‐fluorescence changes. The indicator 9AA was found t be nontoxic to yeast cells at concentrations used to measure pHi (7 μM). The fluorescence of nicotinamide adenine dinucleotide (NADH) molecules did not interfere significantly with the measurement of 9AA‐fluorescence. The pHi change in yeast cell following the addition of a proton ionophore carbonyl cyanide m‐chlorophenyl hydrazone (CCCP) measured by 9AA compared favorably with that measured by the well‐established pHi, indicator (which is however unsuitable for on‐line applications in a bioreactor) bis‐carboxyethyl carboxy fluorescein (BCECF). The pHi of yeast under substrate starved conditions was 6.4 units. The responses of pHi of yeast cells to induced metabolic transitions were studied. Under aerobic condition, pHi increased by 0.12 unit following a 100‐ppm glucose pulse addition and by 0.25 unit following a 300‐ppm ethanol pulse addition. Under anaerobic condition, pHi increased by 0.1 unit following a 500‐ppm glucose pulse addition. Comparison of pHi with other indicators of cellular metabolic state suggests that pHi is a cellular metabolic state indicator. © 1993 John Wiley & Sons, Inc.
Kinetics and modeling of hexavalent chromium reduction in enterobacter cloacae
Authors: Yamamoto Koji , Kato Junichi , Yano Takuo , Ohtake Hisao 
Published: December 2004

AbstractKinetics of bacterial reduction of toxic hexavalent chromium (chromate: CrO42−) was investigated using batch and fedbatch cultures of Enterobacter cloacae strain HO1. In fedbatch cultures, the CrO42− feed was controlled on the basis of the rate of pH change. This control strategy has proven to be useful for avoiding toxic CrO42− overload. A simple mathematical model was developed to describe the bacterial process of CrO42− reduction. In this model, two types of bacterial cells were considered: induced, CrO42−‐resistant cells and uninduced, sensitive ones. Only resistant cells were assumed to be able to reduce CrO42−. These fundamental ideas were supported by the model predictions which well approximated all experimental data. In a simulation study, the model was also used to optimize fed‐batch cultures, instead of lengthy and expensive laboratory experiments. © 1993 John Wiley & Sons, Inc.
The effect of aqueous surfactant solutions on alcohol dehydrogenase (LADH)
Authors: Creagh A. L. , Prausnitz J. M. , Blanch H. W. 
Published: December 2004

AbstractAlcohol dehydrogenase (LADH) was studied in aqueous solutions of surfactants to determine its structural and catalytic characteristics. Fluorescence, circular dichroism (CD), and electron paramagnetic resonance (ERP) techniques were used to study structural changes to the enzyme. The activity of LADH in catalyzing the oxidation of ethanol was investigated. Short‐chain alkyl sulfonates and sulfates did not deactivate LADH or alter its structure. Longer and branched alkyl sulfates and sulfonates, as well as a cationic surfactant (CTAB), affected both LADH activity and conformation. © 1993 John Wiley & Sons, Inc.
Variation and modeling of the probability of plasmid loss as a function of growth rate of plasmid‐bearing cells of Escherichia coli during continuous cultures
Authors: Mosrati Ridha , Nancib Nabil , Boudrant Joseph 
Published: December 2004

AbstractA large number of models concerning cultures of genetically engineered bacteria have been described. Among them, some are specifically adapted to continuous cultures and lead to the determination of two variables: (i) the difference in the specific growth rates between plasmid‐carrying cell and plasmid‐free cells (δμ) and (ii) the frequency of plasmid loss by plasmid‐containing cells (prμ+). Until now, studies have been performed on the global expression prμ+ and δμ, whose value during continuous assays have been supposed approximately constant (mean value) and not on separate values of both terms pr and μ+, respectively, probability of plasmid loss and specific growth rate of the plasmid‐carrying cells. So far these studies do not allow examination of the relationship between these two last parameters. Experimental results were obtained with Escherichia coli C600 galk (GAPDH), a genetically engineered strain that synthetizes an elevated quantity of glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH). From data obtained during continuous cultures, it is shown that during an assay, δμ, and prμ+ do not remain constant. An appropriate mathematical analysis of the expression of μ− (specific growth rate of the plasmid‐free cells) and μ+ has been built up. This allows the evaluation of the values of μ+ and μ− during the continuous cultures carried out at different dilution rates. Values of pr have been calculated from these data. Indeed our results show that pr increases with μ+. A modeling approach which allows correct simulation of this variation is also proposed. This model is derived from the Hill equation regarding cooperative binding of enzymic type reaction. © 1993 John Wiley & Sons, Inc.
Action of lipolytical enzymes in biphasic organic‐aqueous systems: Dynamics of the irreversible Michaelis–Menten reaction
Authors: Tsai Shau‐Wei , Wei Hwa‐Jou , Chiang Chen‐Li 
Published: December 2004

AbstractThrough simple model analysis, the mass action kinetic model for lipolytic enzymes in biphasic aqueous‐organic systems can be simplified using the quasi–steady state assumption (or the quasi–equilibrium state assumption) for the adsorbed enzyme E* or the enzyme–substrate complex E*S. Some parameter combinations leading to the above assumptions are derived confirmed by full numerical integration of the whole enzymatic process. The results may be classified into three categories: (1) the quasi–equilibrium state assumption for E*, (2) the quasi–steady state assumption for E*, and (3) the quasi–steady state assumption for E*S. Further simplification for both E* and E*S is also discussed. © 1993 Wiley & Sons, Inc.
An ultrafiltration membrane bioreactor for the lipolysis of olive oil in reversed micellar media
Authors: Prazers D. M. F. , Garcia F. A. P. , Cabral J. M. S. 
Published: December 2004

AbstractThe enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of dioctyl sodium sulfosuccinate (AOT) in isooctane was investigated in an ultrafiltration ceramic membrane reactor of tubular type, operating in a batch mode. Water concentration was found to be a critical parameter in the enzyme kinetics and hydrolysis yield of the reaction. The size of micelles, recirculation rate, and substrate concentration were found to be the major factors affecting the separation process. A correlation that enables the prediction of final conversion degrees in this bioreactor from the initial reaction conditions was established. © 1993 Wiley & Sons, Inc.
Computation of pH evolution versus ionic products concentration in a fermentation broth
Authors: Kennes C. , Naveau H. , Nyns E. J. 
Published: December 2004

AbstractAn algorithm developed for pH computation has been tested to calculate the theoretical pH changes in a culture medium during the course of a fermentation. A divergence between the computed pH value and the value measured with the electrode allows us to highlight the presence of undetected ionic products. The calculation with the algorithm by means of a computer requires only the knowledge of the ionic properties of the substrates and detected products and existing thermodynamic constants. © 1993 Wiley & Sons, Inc.