bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyelectrolyte precipitation of proteins: II. Models of the particle size distributions
Authors: Fisher Rod R. , Glatz Charles E. 
Published: December 2004

AbstractA population‐balance model has been used to characterize continuous polyelectrolyte precipitation of egg white proteins. We have modeled the particle size distributions of aggregates formed under a range of mixing conditions. The models, accounting for aggregate growth (by both shear‐driven and Brownian‐like collisions), breakage (by hydrodynamic shear or aggregate‐aggregate collisions), and birth (by the breakage of large aggregates), fit the data well. The kinetic constants show dependencies on shear rate and residence time that have not been previously theoretically predicted; these dependencies are due in part to aging effects on the aggregate. The model constants show a dominance of growth over breakage, supporting qualitative interpretations of the particle size distributions. A mechanism for growth‐rate enhancement, caused by polymer extensions from the particle surfaces, produced improved model performance. A collisional breakage mechanism is supported.
Acyl group transfer by proteases forming acyl–enzyme intermediate: Kinetic model analysis
Authors: Yu. Gololobov M. , Borisov I. L. , Belikov V. M. , Švedas V. K. 
Published: December 2004

AbstractA kinetic model of peptide synthesis via transfer of the acyl moiety from activated derivatives of amino acids (S) to nucleophiles (N) catalyzed by proteases forming an acyl–enzyme intermediate has been analyzed. The kinetic model takes into account the subsequent enzymatic hydrolysis of synthesized peptide (P), and so the kinetic curve for this compound shows a maximum (denoted as pmax). Particular stress is placed on analyzing the effects of initial concentrations and of kinetic constants on the value of pmax.The analysis has demonstrated that at a given ratio of initial S and N concentrations, pmax is affected only by (i) the ratio of the second‐order rate constants for enzymatic hydrolysis of S and P(α) and (ii) the ratio of rate constants for an attack of the acyl–enzyme intermediate by the nucleophile and water (β). These conclusions apply regardless of the existence of linear inhibition by the components of the reaction mixture. Thus, the kinetically controlled maximum yield of peptide (pmax) can be calculated a priori from values of α and β that can be estimated experimentally or from reference data. Simple analytical expressions were obtained, allowing a fairly accurate prediction of pmax for a broad spectrum of S and N initial concentrations.
Diffusion of sucrose and yohimbine in calcium alginate gel beads with or without entrapped plant cells
Authors: Pu H. T. , Yang R. Y. K. 
Published: December 2004

AbstractThe diffusion characteristics of sucrose, a nutrient, and yohimbine, a secondary metabolite, in alginate gel beads, with or without entrapped periwinkle (Catharanthus roseus) or apple (Malus domestica) cells, were investigated. Effective diffusivities of both solutes in the gel beads were determined by two different methods from transient concentration changes in well‐stirred solutions where the beads were suspended. The linear plot method developed in this work is easy to use and requires no data from the initial periods of diffusion experiments. It was found that while the cell‐free beads provided only minor diffusional resistance to both solutes, the effective diffusivities of both solutes decreased significantly with the presence of cells in the beads and the amount of reduction was proportional to the amount of cell loading. Further, the effective diffusivity of sucrose appeared to be slightly larger than that of yohimbine under identical conditions. It was also observed that permeabilization of apple cells with dimethyl sulfoxide (DMSO) led to an increase in effective diffusivity with the effect being more significant for yohimbine.
Optimum fiber spacing in a hollow fiber bioreactor
Authors: Chresand Thomas J. , Gillies Robert J. , Dale Bruce E. 
Published: December 2004

AbstractA high surface area hollow fiber reactor was developed for mammalian cell culture. The reactor employs an interfiber gel matrix of agar or collagen for cell support. A model was developed to predict cell density as a function of fiber spacing. Optimum spacings are calculated for two sizes of Celgard hollow fibers. Ehrlich Ascites Tumor (EAT) cells were grown to an estimated density of 1.1 × 108 viable cells/mL in the extracapillary space—corresponding to an overall reactor density of 7 × 107 cells/mL. On the basis of available kinetic and diffusivity data, the model predicts that lactate accumulation may limit cell growth in the early stage of medium utilization, while oxygen delivery becomes limiting at later stages.
Uptake rate of phenol by Pseudomonas putida grown in unsteady state
Authors: Sokół W. 
Published: December 2004

AbstractThe uptake rate of phenol by washed cells of Pseudomonas putidagrown on phenol in fermenter in an un steady state, caused by the step increase of dilution rate and/or phenol concentration in the feed, was studied. The Monod‐Haldane type equation was applied to fit the data and the best kinetic parameters were calculated by nonlinear least‐square techniques. It was found that the minimum period of unsteady state required for induction of the phenol metabolic pathway was approximately 30 min. The values of kinetic parameters in an unsteady state varied according to each parameter. The values of um first monotonically increased to reach their highest value after about 120 min and then monotonically decreased to equal the um in new steady state after about five residence times. No regularity in changing of Ks and Ki, in unsteady state was observed. However, the greatest change in the values of Ki, was 45% while the change in values of Ks was as much as two times compared to Ki and Ks in steady state prior to disturbance.
Control of Escherichia coli–Candida utilis continuous, competitive mixed‐culture system using the dynamic matrix control algorithm
Authors: Goochee Charles F. , Hatch Randolph T. , Cadman Theodore W. 
Published: December 2004

AbstractThe control of the continuous, competitive mixed culture of the yeast Candida utilis (ATCC 8205) and the bacterium Escherichia coli B/r (ATCC 12407) was examined. A modified version of the dynamic matrix control (DMC) algorithm was tested in simulation and then was successfully implemented. This represents the first report of the location and stabilization of a competitive mixed culture at a metastable equilibrium point using automatic control.
Substrate‐dependent differences in production of extracellular matrix molecules by squamous carcinoma cells and diploid fibroblasts
Authors: Varani James , Fligiel Suzanne E. G. , Inman Dennis R. , Helmreich David L. , Bendelow Matthew J. , Hillegas William 
Published: December 2004

AbstractTwo human squamous carcinoma cell lines and human diploid fibroblasts were examined for the production of extracellular matrix (ECM) molecules including fibronectin (FN), laminin (LN), and thrombospondin (TSP) when grown on a number of different substrates. The substrates used included glass, plastic, collagen (gelatin), and DEAE‐dextran. Levels of TSP as indicated by enzyme‐linked immunosorbent assay did not vary significantly as a function of substrate. In contrast, LN levels in the culture medium were significantly decreased when the cells were grown on DEAE‐dextran or collagen‐linked dextran as compared to the other substrates. FN levels were slightly lower in the culture medium of the cells grown on DEAE‐dextran. Biosynthetic labeling followed by immunoprecipitation indicated that the reduction in LN was due, in part, to decreased biosynthesis. Previous studies have indicated that LN influences the behavior of epithelial cells in culture and that the cells, themselves, are a major source of the LN. The differences in LN production noted here indicate that the production of this ECM component is influenced by the substratum on which the cells are grown. These differences could contribute to alterations in biological properties that are known to be influenced by the substratum.
Continuous production of kyotorphin
Authors: Flörsheimer Andreas , Kula Maria‐Regina , Schütz Hans‐Jürgen , Wandrey Christian 
Published: December 2004

AbstractThe continuous α‐chymotrypsin‐catalyzed peptide synthesis of kyotorphin, tyrosyl‐arginine, via the Nα formyltyrosyl‐arginine propyl ester is described. For continuous process development, two reaction systems were studied: immobilized α‐chymotrypsin covalently bound to Eupergit C packed in a column, and soluble α‐chymotrypsin utilizing an enzyme membrane reactor. Selectivities and kinetic parameters are discussed. The use of soluble enzyme in an enzyme membrane reactor proved superior to the covalently immobilized enzyme. A significant loss of enzyme activity and a certain decrease of selectivity was observed during immobilization. It was shown that the addition of organic solvent, in this case n‐propanol, causes a severe diminuation of the enzyme activity.
Solubilization of soybean mitochondria in AOT/isooctane water‐in‐oil microemulsions
Authors: Hochkoeppler Alejandro , Luisi Pier Luigi 
Published: December 2004

AbstractThe water‐in‐oil microemulsion system bis(2 ethyl‐hexyl‐sodium‐succinate (AOT)/isooctane/water is able to solubilize soybean nodules mitrochrondria. Transparent and thermodynamically stable hydrocarbon solutions are obtained, which can be assayed for mitochondrial activity just as aqueous solutions. Malate dehydrogenase (MDH) activity was measured in vivo and gave in reverse micelles very similar results as in water. However the kinetic behavior of this reaction in AOT/isooctane reverse micelles shows some differences with respect to water. Mitochondria in reverse AOT micelles are able to retain about 70% of their initial MDH activity after three days. Mitochondria can be back‐transferred from reverse micelles to water and show respiratory activity almost identical to the native organelles. Electron microscopy studies show that the dimensions of mitochondria back‐transferred into water from AOT micelles are comparable to the dimensions of the native organelles.
Evidence for nitrogen catabolite repression during citric acid production by Aspergillus niger under phosphate‐limited growth conditions
Authors: Dawson M. W. , Maddox I. S. , Brooks J. D. 
Published: December 2004

AbstractExperiments performed in batch fermentation under phosphate‐limited growth conditions showed that the citric acid yield was inversely related to the excess nitrogen concentration in the medium. Results from chemostat culture confirmed a negative relationship between the citric acid yield and both the specific growth rate and the nitrogen consumption rate. This is evidence for nitrogen catabolite repression. A fed‐batch fermentation performed under dual phosphate/nitrogen limitation produced results very similar to those from a culture limited by nitrogen alone. There is no advantage in maintaining an excess of phosphate during citric acid production and the process will therefore be more economic when operated under dual limitation conditions.
Evaluation of thermotolerant yeasts in controlled simultaneous saccharifications and fermentations of cellulose to ethanol
Authors: Spindler Diane D. , Wyman Charles E. , Grohmann Karel 
Published: December 2004

AbstractSimultaneous saccharification and fermentation (SSF) experiments were performed at selected temperatures (37, 41, and 43°C) to obtain comprehensive material balance and performance data for several promising strains of thermotolerant yeast. Parameters measured were ethanol concentration, yeast cell density, and residual sugar and cellulose concentrations. The three yeasts Saccharomyces uvarum, Candida brassicae, and C. lusitaniae and two mixed cultures of Brettanomyces clausenii with S. cerevisiae (mixed culture I) and C. Iusitaniae with S. uvarum (mixed culture II) exhibited rapid rates of fermentation, high ethanol yields, strong viability, or high cellobiase activity. Overall, mixed culture II at 41°C performed better than either component yeast by themselves because it combined a cellobiose fermenting capability with the high ethanol tolerance and rapid glucose fermentation of conventional industrial yeasts. Thus, the mixed cultures provide good initial rates by preventing buildup of cellobiose (a strong inhibitor of enzyme activity) while attaining high ultimate yields of ethanol for high cellulase concentrations. However, C. brassicae and S. uvarum gave similar results to mixed culture II at 37°C.
Desorption of Trichoderma reesei cellulase from cellulose by a range of desorbents
Authors: Otter D. E. , Munro P. A. , Scott G. K. , Geddes R. 
Published: December 2004

AbstractThe desorption of Trichoderma reesei cellulase from Avicel by a wide range of desorbents was measured. Emphasis was placed on desorption at alkaline pH. A maximum desorption of 65–68% Avicelase activity was achieved by contact with NaOH, pH 10.0, at 40°C for 5 min in the presence of 0.005% Triton X‐100 or Tween 80. The design of a suitable desorption process using these conditions is discussed. Glycerol was also effective as a desorbent either alone or in combination with alkali and detergent. However, relatively high concentrations of glycerol were needed and the maximum desorption achieved, 68%, was not significantly greater than that with only alkali and detergent.
Purification of wheat germ agglutinin using affinity flocculation with chitosan and a subsequent centrifugation or flotation step
Authors: Senstad C. , Mattiasson B. 
Published: December 2004

AbstractAffinity purification is by tradition almost equivalent to affinity chromatography. In this report, a purification process is described in which the affinity interaction is performed in free solution. A precipitation step follows, thereby separating the affinity bound material from free. Chitosan is used as a natural polyligand rich in N‐acetyl‐D‐glucosamine and is, because of its specificity, used in affinity precipitation of wheat germ agglutinin (WGA). The polyligand is soluble at pH below 6.5 and precipitates at higher values, thus coprecipitating associated WGA. A process was developed where the overall yield of WGA was 70% and the final product gave a single band on SDS‐PAGE. The process was also run on a larger scale, where even affinity flotation was included in the study as an alternative way to harvest the precipitate. Scaling up the affinity precipitation was a very easy task.
Effects of temperature on the hydrolysis of lactose by immobilized β‐galactosidase in a capillary bed reactor
Authors: Peterson R. S. , Hill C. G. , Amundson C. H. 
Published: December 2004

AbstractThe effects of temperature on the hydrolysis of lactose by immobilized beta‐galactosidase were studied in a continuous flow capillary bed reactor. Temperature affects the rates of enzymatic reactions in two ways. Higher temperatures increase the rate of the hydrolysis reaction, but also increase the rate of thermal deactivation of the enzyme. The effect of temperature on the kinetic parameters was studied by performing lactose hydrolysis experiments at 15, 20, 25, 30, and 40°C. The kinetic parameters were observed to follow an Arrhenius‐type temperature dependence. Galactose mutarotation has a significant impact on the overall rate of lactose hydrolysis. The temperature dependence of the mutarotation of galactose was effectively modelled by first‐order reversible kinetics. The thermal deactivation characteristics of the immobilized enzyme reactor were investigated by performing lactose hydrolysis experiments at 52, 56, 60, and 64°C. The thermal deactivation was modelled effectively as a first order decay process. Based on the estimated thermal deactivation rate constants, at an operating temperature of 40°C, 10% of the enzyme activity would be lost in one year.
Protein partitioning in two‐phase aqueous polymer systems
Authors: Baskir Jesse N. , Hatton T. Alan , Suter Ulrich W. 
Published: December 2004

AbstractTheories of protein partitioning in two‐phase polymer systems which account for the effects of different aspects of system composition—such as the choice of materials, protein size, polymer molecular weight, polymer concentration, salt concentration, and affinity ligands—are reviewed. Although the present models provide some information about specific aspects of partitioning, a comprehensive and fundamental theory which can be used to predict protein partitioning behavior has not yet been developed. Some recommendations for future work are given.
Effects of pH and acetic acid on homoacetic fermentation of lactate by Clostridium formicoaceticum
Authors: Tang I‐Ching , Okos Martin R. , Yang Shang‐Tian 
Published: December 2004

AbstractClostridium formicoaceticum homofermentatively converts lactate to acetate at 37°C and pH 6.6–9.6. However, this fermentation is strongly inhibited by acetic acid at acidic pH. The specific growth rate of this organism decreased from a maximum at pH 7.6 to zero at pH 6.6. This inhibition effect was found to be attributed to both H+ and undissociated acetic acid. At pH values below 7.6, the H+ inhibited the fermentation following non‐competitive inhibition kinetics. The acetic acid inhibition was found to be stronger at a lower medium pH. At pH 6.45–6.8, cell growth was found to be primarily limited by a maximum undissociated acetic acid concentration of 0.358 g/L (6mM). This indicates that the undissociated acid, not the dissociated acid, is the major acid inhibitor. At pH 7.6 or higher, this organism could tolerate acetate concentrations of higher than 0.8M, but salt (Na+) became a strong inhibitor at concentrations of higher than 0.4M. Acetic acid inhibition also can be represented by noncompetitive inhibition kinetics. A mathematical model for this homoacetic fermentation was also developed. This model can be used to simulate batch fermentation at any pH between 6.9 and 7.6.
Diosgenin formation by freely suspended and entrapped plant cell cultures of Dioscorea deltoidea
Authors: Robertson G. H. , Doyle L. R. , Sheng P. , Pavlath A. E. , Goodman N. 
Published: December 2004

AbstractAltered phosphorus concentration, oxygen supply rate, and programmed addition of sucrose and phosphorus were applied to Dioscorea deltoidea plant cells in airlift suspension to increase the formation of the secondary metabolite diosgenin. A low oxygen supply rate (kla′ of 3.9 h−1) completely inhibited formation of diosgenin. A high oxygen supply rate (kla′ of 17.1 h−1) led to the greatest formation of diosgenin in 30 g/L sucrose when the sucrose‐to‐phosphorus mole ratio was 42.5:1. Programmed addition of nutrients over a 15‐day period reduced growth of cell mass relative to diosgenin mass. Intentional aggregation by entrapment of virtually all cells in reticulated polyurethane foam led to reduced cell‐mass yield, diosgenin yield and concentration relative to suspended cells at the same conditions. Entrapment of a small fraction of the cells led to a delayed development of a suspension culture and to formation of significantly higher concentrations of diosgenin. Nearly all of this increase was attributable to the suspended cells. This result suggested sequestering of nonproductive cells by the matrix or sequestering of important nutrients by the matrix‐bound cells. Entrapped cells attained densities of 40 g/L in the matrix.
Localization of cloned invertase in Saccharomyces cerevisiae directed by the SUC2 and MFα1 signal sequences
Authors: Marten Mark R. , Seo Jin‐Ho 
Published: December 2004

AbstractProtein localization in Saccharomyces cerevisiae was studied with two plasmid systems used as a model: one containing the SUC2 structural gene fused with the MFα1 (α‐factor) promoter and signal‐sequence, the other containing the entire SUC2 gene. Special emphasis was placed on the effect of promoter/signal‐sequence (SUC2 vs. MFα1) on the efficiency of invertase transport. The MFα 1 and SUC2 signal sequences were capable of transporting, respectively, 83% and 77% of cloned invertase out of the cytoplasm. However, the SUC2 promoter was easier to control since a six‐fold enhancement of the transported invertase activity associated with derepression was achieved in response to a glucose concentration change from 10 to 2 g/L Cloning on a multicopy plasmid resulted in a four‐fold increase in total specific invertase activity over the wild type yeast strain (which harbors a single copy of the SUC2 gene on the chromosome), whereas the chromosomal site was more efficient for invertase localization yielding over 90% of the invertase transported out of the cytoplasm. Transient experiments done with the SUC2 signal‐sequence‐containing plasmid showed that the specific invertase activity in the periplasmic space reached a maximum three hours after derepression, then decreased very slowly with an accompanying gradual increase in invertase activity in the growth medium.
The use of reverse micelles for the simultaneous extraction of oil and proteins from vegetable meal
Authors: Leser Martin E. , Luisi Pier Luigi , Paimieri Sandro 
Published: December 2004

AbstractA method for the simultaneous extraction of oil and proteins from vegetable meals is presented. The method uses hydrocarbon reverse micelles, so that the oil is extracted directly into the hydrocarbon phase and the proteins are solubilized in the water pools of the reverse micelles. The surfactant used is bis (2‐ethylhexyl) sodium sulfosuccinate (AOT) in isooctane at variable w0 values (w0 measures the amount of water in the system, where w0 = [H2O]/[AOT]). A comparison with the usual extraction methods is offered. It is shown that with the micelle system the extraction of oil is as large as with the usual methods, and it is independent of w0. However the amount and type of proteins extracted depends strongly on w0. At w0 values below 6, no protein and only low molecular weight compounds (i.e. chlorogenic acid) are extracted, at larger water content (i.e. by increasing the dimension of the micelle water pool), also proteins are solubilized in a significant amount and with a molecular weight which increases by increasing W0. The protein solubilized in the microemulsion system can be recovered into an aqueous phase with a back‐transfer step.
Syntheses and applications of water‐soluble reactive polymers for purification and immobilization of biomolecules
Authors: Nguyen A. L. , Luong J. H. T. 
Published: December 2004

AbstractReactive polymers have been prepared by copolymeriz‐ing N‐isopropyl acrylamide (NIPAM) with N‐acryloxy‐succinimide (NASI) or glycidyl methacrylate (GMA). The amino groups of ligands could react with the residues of NASI or GMA and the polymers could be precipitated by temperature and/or salinity variation, since they contained the NIPAM residues. As a model, p‐aminobenza‐midine, a trypsin inhibitor, was attached to the polymers to form water‐soluble macroligands, capable of selectively binding trypsin from a trypsin–chymotrypsin solution. After precipitation of the macroligand–trypsin complex, followed by dissociation, approximately 82% trypsin was isolated. The NIPAM‐GMA copolymer was also reacted with immunogammaglobulin (IgG) and alkaline phosphatase (AP). It was demonstrated that the IgG bearing polymer was able to bind protein A and the whole complex was precipitable. The reactive polymer was also used for direct immobilization of AP which was active in repeated reactions.