bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fundamental studies of biomolecule partitioning in aqueous two‐phase systems
Authors: Diamond Alan D. , Hsu James T. 
Published: December 2004

AbstractPhase diagram data at 4°C was determined for the aqueous two‐phase systems composed of polyethylene glycol, dextran, and water. The Flory–Huggins theory of polymer thermodynamics was used to correlate partitioning of biomolecules in these aqueous two‐phase systems resulting in a simple linear relationship between the natural logarithm of the partition coefficient and the concentration of polymers in the two phases. This relationship was verified by partitioning a series of dipeptides which differ from one another by the addition of a CH2 group on the c‐terminal amino acid residue and by utilizing a set of low‐molecular‐weight proteins. The slope of the line could be expressed in terms of the interactions of the biomolecule with the phase forming polymers and water. The main result for the dipeptides was that knowledge of the partition coefficient in any of the PEG/dextran/water systems, regardless of polymer molecular weight, enabled prediction of the coefficient in all of the systems. The dipeptides were also used for determination of the Gibbs free energy of transfer of a CH2 group between the phases. This quantity was correlated with polymer concentration, thus establishing a hydrophobicity profile for the PEG/ dextran/water systems. The methodology for predicting dipeptide partition coefficients was extended to proteins, where it was found that low‐molecular‐weight proteins gave a linear relationship with the tie line compositions of a phase diagram.
Shear degradation as a probe of microalgal exopolymer structure and rheological properties
Authors: Ramus J. , Kenney B. E. 
Published: December 2004

AbstractThe bulk theological properties of exopolymers produced by three species of microalgae are destroyed by shear stress. The properties are drag reduction in capillary pressure flow and low shear rate viscosity. As such, shear stress constitutes an experimental probe into the macromolecular structure which effects bulk Theological properties. Native and sheared exopolymer solutions were subjected to analysis by electrophoresis, size exclusion chromatography, hydrolysis, dialysis, and reducing end‐group analysis. The evidence indicates that shearing did not break the glycoside backbone of these exopolymers, rather shearing disrupted subtle interactions between copolymers. The interactions necessary for bulk rheological properties are likely at the quaternary level of macromolecular organization, specifically weak aggregations.
Stability testing of ligninase and Mn‐peroxidase from Phanerochaete chrysosporium
Authors: Aitken Michael D. , Irvine Robert L. 
Published: December 2004

AbstractThe white‐rot fungus Phanerochaete chrysosporium produces extracellular peroxidases (ligninase and Mn‐peroxidase) believed to be involved in lignin degradation. These extracellular enzymes have also been implicated in the degradation of recalcitrant pollutants by the organism. Commercial application of ligninase has been proposed both for biomechanical pulping of wood and for wastewater treatment. In vitro stability of lignin degrading enzymes will be an important factor in determining both the economic and technical feasibility of application for industrial uses, and also will be critical in optimizing commercial production of the enzymes. The effects of a number of variables on in vitro stability of ligninase and Mn‐peroxidase are presented in this paper. Thermal stability of ligninase was found to improve by increasing pH and by increasing enzyme concentration. For a fixed pH and enzyme concentration, ligninase stability was greatly enhanced in the presence of its substrate veratryl alcohol (3,4‐dimethoxybenzyl alcohol). Ligninase also was found to be inactivated by hydrogen peroxide in a second‐order process that is proposed to involve the formation of the unreactive peroxidase intermediate Compound III. Mn‐peroxidase was less susceptible to inactivation by peroxide, which corresponds to observations by others that Compound III of Mn‐peroxidase forms less readily than Compound III of ligninase.
Growth yield, maintenance requirements, and lipid formation in the oleaginous yeast Apiotrichum curvatum
Authors: Ykema Adrie , Bakels Ronald H. A. , Verwoert Ira I. G. S. , Smit Henk , van Verseveld Henk W. 
Published: December 2004

AbstractFor guiding and improving the efficiency of the production of lipid, complete insight into the flow of carbon and energy during growth and product formation is necessary. Therefore, data have been collected to determine various important growth parameters for the oleaginous yeast Apiotrichum curvatum. Chemostat experiments at specific growth rates, ranging from 0.05 to 0.15 h−1 and recycling experiments with 100% biomass retention, with growth rates decreasing from 0.10 to 0.004 h−1, demonstrated that maintenance requirements of A. curvatum are very low, compared to maintenance requirements described for other yeasts as Saccharomyces cerevisiae and Candida parapsilosis.It also appeared that growth and lipid production are proportional to substrate consumption when specific growth rates are higher than approximately 0.02 h−1, but that lipid production stops at growth rates below this value. The practical consequences of these data are that fed batch cultures, which are often applied in fermentation industry, can only be useful with lipid producing yeasts when the growth rate in the process is carefully monitored to ensure specific growth rates higher than 0.02 h−1. Dilution of the culture, partial recycling and/or a continuously increasing nutrient feed are solutions for the expected problems at low growth rates.
Optimization of Escherichia coli growth by controlled addition of glucose
Authors: Robbins J. W. , Taylor K. B. 
Published: December 2004

AbstractDuring aerobic growth of Escherichia coli (recombinant K‐12 and strain B) on protein hydrolysate (L‐broth) and a carbon source (glucose), acetic acid is produced via glucose metabolism until the late log phase. At this point, the culture pH starts to increase and the growth rate decreases. In cultures without further glucose supplementation, these changes are associated with the accumulation of ammonia, the utilization of acetic acid, the depletion of amino acids, and the complete depletion of glucose. We hypothesize that, after depletion of the glucose, the bacteria catabolize amino acids for energy and carbon and give off the nitrogen as ammonia. Also contributing to the overall increase in pH is the depletion of the acetic acid produced earlier as it is metabolized upon exhaustion of glucose. However, there is a lag time of about 1 hour after the initial pH increase before the sustained accumulation of ammonia begins. This lag indicates that an unidentified factor, in addition to the increase in ammonia, contributes to the increase in pH. Advantage was taken of the turnaround from acid production to base production as reflected in the culture pH to implement the addition of glucose. In growth experiments during which the pH was controlled in the basic direction by glucose addition, the observed decrease in growth rate was significantly postponed and the pH change in the basic direction was reversed as a result of acid production by the cells from the newly added glucose. Furthermore, coll densities of twice that obtained without glucose feeding were demonstrated. Based on the media cost per unit cell density, the data indicate a 31% cost savings.
Immobilized enzyme cellulose hollow fibers: III. Physical properties and in vitro biocompatibility
Authors: Comfort Ann R. , Berkowitz Sharon , Albert Elizabeth , Langer Robert 
Published: December 2004

AbstractThe initial testing of the safety of a cellulose–heparinase hollow fiber device was assessed with respect to physical properties and in vitro biocompatibility. The material cleared urea and creatinine without passing albumin, even at high flow rates. The clearance of urea and creatinine by cellulose–heparinase was equal or slightly reduced in comparision to the cellulose device. The cellulose–neparinase device tolerance to now rates was also unchanged. In addition, scanning electron microscopy of the lumen established the uniformity of the material. The analysis of clearance rates and the scanning electron micrographs show there to be no damage to the cellulose membrane after tresyl chloride activation and heparinase immobilization. The investigation of biocompatibility in an in vitro test system with whole human blood indicated that there were no significant changes in the biocompatibility of cellulose with bound heparinase. There was no change in the level of red blood cells, white blood cells, or platelets over the course of in vitro whole blood perfusion through cellulose or cellulose–heparinase hollow fiber devices. Low levels of plasma hemoglobin and complement activation were observed with cellulose and cellulose–heparinase devices. Thus, the cellulose hollow fibers can be functionalized without any changes in in vitro performance.
Isolation of urokinase by affinity ultrafiltration
Authors: Male K. B. , Nguyen A. L. , Luong J. H. T. 
Published: December 2004

AbstractA water‐soluble, ligand‐bound polymer has been synthesized for the purpose of isolation of urokinase, an important plasminogen activator. The affinity polymer was formed by copolymerizing N‐acryloyl‐m‐aminobenza‐midine and acrylamide in the absence of oxygen. An affinity ultrafiltration process was then developed for isolating urokinase from an artificial solution containing peroxidase and urokinase and from a crude urine source. The process yields were determined to be 86% and 49%, respectively. The recovered urokinase exhibited a specfic activity close to that of the highest commercial grade. This article also presents a new technique for assaying urokinase by coupling plasminogen with L‐benzoyl arginine‐p‐nitroanilide (L‐BAPNA), an inexpensive chromogenic substrate.
Mathematical modeling of the effects of ammonium ion on the intracellular pH of hybridoma cells
Authors: McQueen Anne , Bailey James E. 
Published: December 2004

AbstractA mathematical model for the effects of NH4Cl addition to the growth medium on hybridoma cell intracellular pH (pHi) is presented which includes a detailed description of the properties of the Na+/H+ exchanger. The model is used to calculate the steady‐state value of pHi as a function of the extracellular NH4Cl concentration, employing parameter values taken from the literature except for the cell permeability to NH4+ This parameter value, estimated to be 3.5 × 10−7 cm/s, is obtained by fitting simulation results to experimental data obtained previously for the steady‐state value of pHi in the presence of 10mM NH4Cl. The model simulates well the major features of previously observed experimental pHi changes following NH4Cl addition: the transient characteristics, dependence on the NH4Cl concentration, and lack of dependence on the external pH value. The effect of parameter variations on model results is also investigated in additional simulations. The general modeling framework employed here should be useful for other types of mammalian cells.
Invertase‐catalyzed reactions in alcoholic solutions
Authors: Selisko Barbara , Ulbrich Renate , Schellenberger Alfred , Müller Ute 
Published: December 2004

AbstractThe formation of alkyl β‐D‐fructofuranosides by invertase from sucrose in aqueous solutions of methanol, ethanol, or n‐propanol is studied for the dependence on alcohol and invertase concentrations as well as on reaction time. The yield of alkyl β‐D‐fructosides is shown to be controlled by three competitive reactions: the alcoholysis of sucrose, the hydrolysis of sucrose, and the hydrolysis of alkyl β‐D‐fructosides. Both the conversion rate of sucrose and the fraction of alkyl β‐D‐fructosides in the product mixture are dependent on the chain length of the alcohols. They decrease in the sequence methanol > ethanol > n‐propanol. Alkyl β‐D‐fructosides are also formed by invertase starting from alcoholic solutions of fructose.
Modeling of immobilized cell reactor for propionic acid fermentation
Authors: Crespo J. P. S. G. , Almeida J. S. , Moura M. J. , Carrondo M. J. T. 
Published: December 2004

AbstractA mathematical model of steady state reactor behavior was developed, combining the tanks‐in‐series model with fermentation kinetic description. The model was tested with experimental data‐from an immobilized cell reactor for propionic acid production operated under different residence times. In order to determine the effects of liquid flow rate and gas evolution on the degree of mixing, residence time distribution studies (RTDs) were performed during fermentation. The tanks‐in‐series model represented adequately the hydrodynamic behavior of the reactor. Association of an intrinsic kinetic model obtained from chemostat studies with the tanks‐in‐series model allows a “chemostat equivalent” cell concentration profile and a substrate consumption profile to be obtained. The advantage of having a two‐level pH adjustment within the reactor is also discussed.
Enhancing penicillin fermentations by increased oxygen solubility through the addition of n‐hexadecane
Authors: Ho Chester S. , Ju Lu‐Kwang , Baddour Raymond F. 
Published: December 2004

Abstractn‐Hexadecane was added to fermentation media to increase the medium oxygen solubilities, thus enhancing oxygen transfer rates in penicillin fermentations. For shake flask fermentations, cells were found to grow faster in the flasks with n‐hexadecane than those without. The addition of n‐hexadecane to penicillin fermentations was shown to significantly increase cell growth and penicillin production and reduce formation of mycelial pellets. The result was attributed to the enhancement of oxygen transfer in mycelial fermentations due to the higher oxygen solubilities of fermentation media achieved by adding n‐hexadecane.
High‐level recombinant protein production in bioreactors using the baculovirus–insect cell expression system
Authors: Caron Antoine W. , Archambault Jean , Massie Bernard 
Published: December 2004

AbstractIn order to develop an efficient process for large‐scale production of recombinant protein, various factors were studied which affect the productivity of Sf‐9 (Spodoptera frugiperda) insect cells when using the baculovirus expression system. It was shown that upon infection with the Bac‐BRV6L recombinant baculovirus, the level per cell of VP6 (a bovine rotavirus nucleocapsid protein) would drop 10‐fold when host cell density at the time of infection increased from 2 × 106 to 3 × 106 cells/mL. The decrease was found to be totally reversible by culture medium renewal after infection, even when cells were infected at the stationary phase. Recombinant protein production was 4–6 times higher using TNMFH medium supplemented with 10% fetal bovine serum (FBS) than in IPL/41 serum‐free medium. Fine‐tuning of infection parameters in a 4‐L surface‐aerated bioreactor resulted in the production of typically 350 mg/L of VP6 protein, representing more than 25% of total cell proteins.
Parametric analysis of the errors associated with the Michaelis–Menten equation
Authors: Brown Russell F. , Holtzapple Mark T. 
Published: December 2004

AbstractBased on the well‐known mechanism describing Michaelis–Menten kinetics, three rate expressions may be developed: the exact solution (Model 1), a rate equation resulting from the pseudo‐steady‐state assumption (Model 2), and Model 2 with the additional assumption that the amount of free substrate is approximately equal to the total amount of substrate (Model 3). Although Model 1 is the most precise, it must be integrated numerically and it requires three experimentally determined parameters. Models 2 and 3, however, are simpler and require only two parameters. Using dimensionless forms of the three models, we have evaluated the errors in the two simplified models relative to the exact solution using a wide range of parameter values. The choice of model for reactor design depends on the initial substrate to enzyme ratio (α0), and on the ratio of the Michaelis–Menten constant to the enzyme concentration (σ). Based on a 2% model error criteria, when α0 > 15 or σ ≥ 100, Model 3 is adequate; if 5 < α0 < 15, or if σ ≥ 10, then Model 2 may be used; and if α0 < 5 and σ < 10, then the exact solution (Model 1) is required.
A simple model to describe transient differences between cell number and biomass growth rates of Escherichia coli
Authors: Rodin J. B. , Lyberatos G. K. , Svoronos S. A. 
Published: December 2004

AbstractInformation on the response of a microbial culture to dynamic environmental conditions is necessary for the design of transient operation processes. However, most attempts at modelling culture response have been directed at describing the steady‐state behavior. Thus, there is a need for adequate dynamic models for process design. Simulations of nutrient shifts were completed using a “single‐cell” model for Escherichia coli. It was discovered that the specific mass growth rate and the specific number of cells growth rate were different under transient conditions, whereas at steady state (balanced growth) these rates are equivalent. Using these observations, a simple delay model to describe the transient behavior of the two growth rates is formulated and tested. The model contains as state variables only the readily measurable macroscopic quantities (biomass, cell number, and limiting nutrient). This model agreed well with the predictions of the single‐cell model.
Methanol biosynthesis by covalently immobilized cells of Methylosinus trichosporium: Batch and continuous studies
Authors: Mehta Perdeep K. , Ghose Tarun K. , Mishra Saroj 
Published: December 2004

AbstractThe DEAE‐cellulose linked cells of Methylosinus trichosporium displaying high specific methane mono‐oxygenase activity (66 μmol methane oxidized/h mg cells) were used for methanol biosynthesis from biogas derived methane in a batch and a continuous cell reactor. The optimum cell‐to‐carrier ratio was determined to be 0.5 g cells/g dry weight cellulose. Batch experiments indicated that 100 mM phosphate ion concentration was necessary to inhibit further oxidation of methanol; excess oxygen supply favored methanol accumulation with an increase in methane conversion efficiency to 27%. A pulse of 40 mM sodium formate at the end of 6 h resulted in restoration of methanol accumulation by regenerating NADH2 required for the sustained activity of methane mono‐oxygenase. Maximum methanol level of 50 μmol/mg cells was obtained in the batch reactor. In a standard 50‐mL ultrafiltration continuous reactor, the covalently linked cells produced methanol at a continuous rate of 100 μmol/h for the first 10 h, after which the methanol accumulation rate fell low due to the depletion of NADH2. The methanol accumulation could be stimulated by supplying sodium formate (40 mM) in either 20 or 100 mM phosphate buffer. Maximum methanol accumulation rate of 267 μmol/h was obtained when 20 mM formate was supplied in the feed stream containing 100 mM phosphate ions, and this level of biosynthesis was maintained for over 72 h. The stoichiometric balance made at various points of formate addition indicated that the molar amount of methanol generated at steady state is dependent on the equimolar addition of sodium formate to the feed. The half‐life t1/2 and thermal denaturation rate constant Kd were computed to be 108 h and 6.42 × 10−3 h−1, respectively.
Complex growth dynamics in batch cultures: Experiments and cybernetic models
Authors: Straight Jeffrey V. , Ramkrishna D. 
Published: December 2004

AbstractThe cybernetic framework developed by Ramkrishna and co‐workers is shown to encompass the regulation of nutrient transport processes as well as the effect of nutrient transport on the biotic phase. A structured model which accounts for both an abiotic or environmental phase and a biotic or cellular phase is proposed to describe bacterial growth on lactose as the limiting carbon and energy source. In the presence of lactose, competing uptake mechanisms are proposed. At low lactose concentrations, an energy‐requiring transport process is the preferred uptake mechanism. The coupling between cellular energetics and nutrient uptake results in an interesting intermittent growth phenomenon. As the concentration of lactose increases, a nonenergetic transport process is preferred and cellular growth ceases to be intermittent. Model simulations are compared with previously reported experimental results and exhibit good agreement over the entire range of initial lactose concentrations.
Papain kinetics in the presence of a water‐miscible organic solvent
Authors: Fernandez Mirtha M. , Clark Douglas S. , Blanch Harvey W. 
Published: December 2004

AbstractThe effects of various concentrations of a water‐miscible organic solvent [a 7:3 (v/v) mixture of N, N dimethylformamide and dimethylsulfoxide] on the kinetics of papain have been investigated. The parameters kcat and Km for the amidase and esterase activity of papain using N‐α‐benzoyl‐DL‐arginine‐p‐nitroanilide (BAPNA) and N‐α‐benzoyl‐L‐arginine ethyl ester (BAEE) as substrates were determined. For both types of activity, kcat initially increased (up to about 15% solvent), and then decreased with increasing concentrations of organic solvent. In contrast, Km increased sharply with the organic solvent concentration. Active site titration at 0 and 50% solvent indicated no change in the amount of active enzyme. Fluorometric measurements of the emission spectrum of papain did not indicate any major conformational changes with increasing concentrations of organic solvent.
Growth, death, and oxygen uptake kinetics of Pichia stipitis on xylose
Authors: Slininger P. J. , Branstrator L. E. , Bothast R. J. , Okos M. R. , Ladisch M. R. 
Published: December 2004

AbstractPichia stipitis NRRL Y‐7124 has potential application in the fermentation of xylose‐rich waste streams, produced by wood hydrolysis. Kinetic models of cell growth, death, and oxygen uptake were investigated in batch and oxygen‐limited continuous cultures fed a rich synthetic medium. Variables included rates of dilution (D) and oxygen transfer (K1a) and concentrations of xylose (X), ethanol (E), and dissolved oxygen (Cox). Sustained cell growth required the presence of oxygen. Given excess xylose, specific growth rate (μ) was a Monod function of Cox. Specific oxygen uptake rate was proportional to μ by a yield coefficient relating biomass production to oxygen consumption; but oxygen uptake for maintenance was negligible. Thus steady‐state COX depended only on D, while steady‐state biomass concentration was controlled by both D and K1a. Given excess oxygen, cells grew subject to Monod limitation by xylose, which became inhibitory above 40 g/L. Ethanol inhibition was consistent with Luong's model, and 64. 3 g/L was the maximum ethanol concentration allowing growth. Actively growing cells died at a rate that was 20% of μ. The dying portion increased with E and X.
Critical assessment of gassing‐in methods for measuring kla in fermentors
Authors: Linek V. , Sinkule J. , Beneš P. 
Published: December 2004

AbstractThe reliability of dynamic measurement methods of kla in fermentors using a step oxygen concentration change in the feed gas was tested. The tests were performed both for the original variant using the nitrogen ⇌ air exchange and the newly presented variant using the oxygen‐enriched air (27 vol % O2) → air exchange. The testing consisted in comparing kla values determined from these methods with values determined from the steady‐state Na2SO3 feeding method and the dynamic pressure method, the reliability of which was proven earlier. The measurements were done in water (coalescent batch) and in 0.5M Na2SO4 solution with and without the addition of 1 wt % carboxymethylcellulose (noncoalescent batches). It was found that in noncoalescent liquids the methods tested give extremely low kla values (as low as 15% of the correct value). The methods are defective in principle irrespective of the gases used for exchange.