bluuebunny/crossref_metadata_2025_split huggingface dataset:
Yeast Alcohol Dehydrogenase Bound to Membranes: Surface and Microenvironment Effects on Activity and Stability
Authors: Kennedy C. L. , Domach M. M. 
Published: March 2005

AbstractThe enzyme, yeast alcohol dehydrogenase, was adsorbed to porous nitrocellulose and nylon membranes. The two membranes provide different surface chemistries as indicated by the results of the streaming potential, enzyme adsorption, and fluorescein isothiocyanate adsorption experiments. The stability of the enzyme, as determined by continually measuring the extent of coenzyme reduction as a function of time, appeared to be much less for the enzyme adsorbed to the positively charged membrane surface. Moreover, the enzyme adsorbed to the positively charged membrane was the least responsive to pulses of the reducing agent, dithiothreitol, and appeared to exhibit the highest transition temperature when subjected to differential scanning calorimetry analysis. These results indicate that the entropically spreading process observed for other adsorbed proteins may be occurring and the process is more rapid and extensive when enzyme is adsorbed to the nylon than the nitrocellulose membrane. In addition to the relative stability of the enzyme on two different surfaces being examined, the effect of the microenvironment on modulating the activity of the enzyme was investigated by using the reversibility of the enzyme‐catalyzed reaction as a probe of the average local environment of the enzyme. It was found that a threshold buffer concentration existed that, once exceeded, the effect of proton production by the reaction could be suppressed.
Product Inhibition Influence on Immobilized Cell Biocatalyst Performance
Authors: Sayles Gregory D. , Ollis David F. 
Published: March 2005

AbstractThe potential steady‐state influence of product inhibition on the performance of immobilized cell cultures is thoroughly explored with the aid of a simple unstructured reaction‐diffusion model. Production inhibition was assumed to diminish the specific growth rate directly. The range of product sensitivity explored corresponds directly with the observed range of ethanol sensitivity of Clostridium thermocellum, Clostridium ace‐tobutylicum, Saccharomyces uvarum, Zymomonas mobilis, and Saccharomyces cerevisiae. The consequent influence on the immobilized cell growth rate, thickness of steady‐state viable cell layer, formation of growth‐associated product, and global performance of the immobilized cell particle is explored by simulated variation of both the external bulk solution product level and the cell intrinsic sensitivity to the inhibitory product. Thus, both the thickness of the steady‐state viable cell layer and the consequent biomass loading of the bead are predicted variables of the model; these are variables due to the adaptive growth and biomass redistribution which occur in porous supports. The calculated influences are appreciable and even dramatic under some circumstances; the implications for packed‐bed reactor operations for ethanol and solvent production are discussed.These model calculations indicate that product inhibition can very significantly influence the performance of immobilized cell particles. Immobilization alone necessarily increases the impact of product inhibition on the culture since intraparticle product levels must be higher that external solution conditions. The presence of product inhibition lowers the specific growth rate of the culture pointwise in the carrier, thus diminishing the particle conversion of substrate to product and the total productivity and specific activity of the biocatalyst. Counterintuitively, perhaps, increased sensitivity to product inhibition results at first in an increased viable biomass loading of each carrier particle; then at still higher sensitivities a decreased loading and eventual extinction of viable cells is predicted. The application of these calculations for packed‐bed reactor design is suggested and constitutes a portion of our ongoing studies.
Enhancing Oxygen Transfer in Surface‐Aerated Bioreactors by Stable Foams
Authors: Ju Lu‐Kwang , Armiger William B. 
Published: March 2005

AbstractTo enhance oxygen transfer in surface‐aeration bioreactors, stabilized foams were generated to increase the gas‐liquid interfacial area by slowly introducing coarse bubbles into media containing fetal bovine serum. The bubble sparging rates were so low (i.e., 20 and 50 mL/h) that the contribution to oxygen transfer from these bubbles was due to foaming instead of bubbling. Furthermore, no physical cell damage caused by bubble sparging was observed. Oxygen transfer coefficients, kLa, in the bioreactors were measured in cell‐free media. Without the foam‐stabilizing agent (i.e., serum), no appreciable change in kLa was observed due to the bubble sparging. On the other hand, with serum, kLa increased with increasing serum content and bubble sparging rate and corresponded well with the degree of foaming. With 10% fetal bovine serum and a bubble sparging rate of 50 mL/h, kLa increased approximately 90% compared with no foaming. The enhancing effect of foam on oxygen transfer in surface aeration bioreactors has been further demonstrated with hybridoma cultures simultaneously grown in three identical bioreactors with and without stabilized foams.
Disintegration of Yeast Cells by Pressurized Carbon Dioxide
Authors: Lin Ho‐Mu , Chan Err‐Cheng , Chen Cheeshan , Chen Li‐Fu 
Published: March 2005

AbstractDisruption of yeast cells with high‐pressure carbon dioxide at both subcritical and supercritical temperatures (25, 35, and 55 °C) was investigated. The experimental results revealed that yeast cells can be ruptured to a maximal level by carbon dioxide within 5 h at 5000 psi and 15 h at 1000 psi at any of the temperatures studied. In the presence of β‐glucuronidase, the length of time for maximal cell rupture was reduced to 90 min at 5000 psi. Off‐flavors of the ruptured yeast cells were removed by carbon dioxide in the process. The functional properties of proteins were preserved, as indicated by enzyme activities in the ruptured cell suspension. An increase in temperature from subcritical to supercritical of carbon dioxide led to a significant enhancement of rapture rates under high pressures, while the functional properties of proteins and the removal of off‐flavors were relatively insensitive to the variation of temperature if the process was maintained at or below 35 °C. At higher temperatures, the activities of enzymes began to decay and were lost at about 55 °C under the carbon dioxide pressures of this study.
Studies on Scale‐Up Parameters of an Immunoglobulin Separation System Using Protein A Affinity Chromatography
Authors: Kang Kyung A. , Ryu Dewey D. Y. 
Published: March 2005

AbstractEffects of operational and system parameters on process scale‐up of murine immunoglobulin (IgG2aκ) purification using Protein A affinity chromatography are investigated. Parameters studied are those related to sample application, elution, ligand concentration on support, and column size change. Between sample application velocities of 0.004 and 0.030 cm/s (16‐108 cm/h), the product concentration profiles in eluate did not show significant differences. With given system parameters, the retention time and bandwidth of the peak could be predicted by moment theory. The mean equilibrium constant during elution showed a strong effect of pH between 2 and 4. Within the range of protein A concentrations studied, 0.15‐1.22 mg/mL of gel, the column capacity shows a linear relationship with the concentration of protein A immobilized. Dimensional scale‐up of the column in the radial direction increased the total purification capacity linearly as the cross‐sectional area increased without increasing pressure drop; however, the product concentration was diluted. Scale‐up of the column dimension in the axial direction enables higher concentrations of product in the eluate, although the retention time increases linearly as the gel height increases.
Isolation of Human B‐Cell Subpopulations for Pharmacological Studies
Authors: Bauer Johann , Stünkel Klaus G. E 
Published: March 2005

AbstractThree groups of human peripheral blood B‐lymphocytes were separated from each other by countercurrent centrifugal elutriation and free‐flow electrophoresis. They differed in their state of maturation and in their capability to produce antibodies in vitro. These B‐cell subpopulations were used to study features of a drug such as BAY R 1005. BAY R 1005 is a synthetic glycolipid analogue (GLA), which is supposed to modulate antibody synthesis. Mature, immunoglobulin‐(Ig‐) secreting B‐lymphocytes secreted equal quantities of antibodies in the presence and in the absence of the GLA. BAY R 1005 was found to be without mitogenic activity on resting B‐cells and did not induce them to produce antibodies. However, it supported the antibody production of preactivated B‐lymphocytes. The in vitro preactivated B‐cells were affected via monocytes. Only in vivo preactivated B‐lymphocytes increased their antibody production under the direct influence of BAY R 1005.
Formation of Bioerodible Polymeric Microspheres and Microparticles by Rapid Expansion of Supercritical Solutions
Authors: Tom Jean W , Debenedetti Pablo G 
Published: March 2005

AbstractPolyhydroxy acids [poly(L‐lactic acid) (L‐PLA),poly(D,L‐lactic acid) (DL‐PLA), and poly(glycolic acid) (PGA)], biocompatible and bioerodible polymers that are being investigated for controlled delivery of pharmaceuticals and are approved by the Food and Drug Administration for in vivo sutures and bone repair implants, have been dissolved in supercritical CO2 and precipitated by rapid expansion of the resulting supercritical solutions (RESS). The formation of these microparticles and microspheres is a first step toward the goal of producing, in a single processing step, drug‐loaded polymeric microspheres for use in controlled release applications. Nucleation of poly(L‐lactic acid) from CO2 and CO2‐acetone mixtures produced microparticles and microspheres ranging from 4 to 25 μm. Microspheres (2‐20 μm) were also obtained with chlorotrifluoromethane as solvent. Commercial L‐PLA precipitated after extraction of low molecular weight oligomers showed degradation kinetics similar to that of the starting material. The precipitation of DL‐PLA from CO2 produced irregular‐sized particles (10‐20 μm). PGA, a polymer insoluble in most organic solvents, was found to be soluble in supercritical CO2. Nucleation of PGA from CO2 produced both regular‐sized particles and needles of 10–40‐μm length. The total solubility of commercial L‐PLA in supercritical CO2 at 250 bar and 55 °C decreased from 0.14 wt % to less than 0.05 wt % and then leveled off as the cumulative flow of CO2 per unit mass of L‐PLA loaded in the extractor increased beyond 20 standard L of CO2/g of L‐PLA. Use of acetone (1 wt %) as a cosolvent increased L‐PLA solubility by ∼500%.
Thermolytical Techniques To Characterize Fungal Polysaccharides and Bacterial Lipopolysaccharides
Authors: Ramos‐Sánchez M. C , Rodríguez‐Torres A , Leal J. A , Martín‐Gil F. J , Martín‐Gil J 
Published: March 2005

AbstractThe present work constitutes an entirely novel contribution in the scope of microbiology and especially in taxonomy, introducing thermolysis curves as a rapid method of characterization of fungal polysaccharides and bacterial lipopolysaccharides. The thermal analysis techniques applied were thermogravimetry and derivative thermogravimetry (TG‐DTG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). Each thermogram of a sample is represented by one or a few temperatures and, in DSC, by complementary enthalpy data. The temperatures of the thermograms from structurally unknown polysaccharides are compared with those used as references, and thus, information on their composition, linkage types, and anomeric configuration can be deduced. The situation is more complicated for bacterial lipopolysaccharides, but in whatever mode, a structural estimation is always possible. In the course of the development and validation of the thermal method, structural findings on relative stabilities of linkage types (valuable in carbohydrate research) have been recognized and are therefore also described in this work.
Effect of Starch Granule Size on Physical Properties of Starch‐Filled Polyethylene Film
Authors: Lim Seung‐Taik , Jane Jay‐Lin , Rajagopalan Shyamala , Seib Paul A. 
Published: March 2005

AbstractPhysical properties of blown films (25‐60‐μm thickness) from compounded mixtures of linear low‐density polyethylene (LLDPE) and starch were investigated. As starch content increased, tensile strength, percent elongation, and light transmittance decreased and film thickness increased. Among the tested films, small‐particle corn starch (2‐μm average diameter) film had the highest elongation rate and tensile and yield strength (560%, 3.15 kg/mm2, and 1.07 kg/mm2, respectively, at 15% starch content). Potato starch (35‐μm average diameter) film had the lowest values (508%, 1.52 kg/mm2, and 0.55 kg/mm2, respectively, at 15% starch content). Potato starch‐LLDPE film had the highest light transmittance and film thickness; small‐particle corn starch had the lowest. Tensile and yield strength of the films had strong negative correlations with average starch granule diameter (R=0.99 and‐0.94, respectively). Film thickness and light transmittance were linearly correlated with starch granule size (R=0.93 and 0.87, respectively). Using small‐particle corn starch substantially increased incorporated starch level in the film while maintaining the film quality.
Microbial Aldonolactone Formation and Hydrolysis: Kinetic and Bioenergetic Aspects
Authors: Noorman H. J. , Rakels J. L. L. , Kuenen J. G. , Luyben K. Ch. A. M. , Heijnen J. J. 
Published: March 2005

AbstractFrom previous work, it was observed that during growth on mixtures of acetate and aldose sugars the growth yield of the bacterium Acinetobacter calcoaceticus was increased when aldonolactone hydrolysis occurred. In this paper, the underlying mechanism was investigated by studying the relationship between cellular yield and lactone hydrolysis in a quantitative way. The literature on the kinetics of acid formation from aldono‐lactones was reviewed. It appears that the reaction pattern is composed of lactone isomerization and hydrolysis steps which occur in series. In the acid pH range, lactone interconversion is the rate‐limiting step for acid formation, whereas above pH 7 hydrolysis is slowest. Only for D‐gluconolactone could the detailed mechanistic kinetics be evaluated. For a number of other aldonolactones, including D‐xylono‐ and D‐galactonolactone, an empirical kinetic equation was derived. The reaction rate constants of these lactones are much smaller than for gluconolactone. The kinetic model for the hydrolysis of xylonolactone was experimentally verified, by application of the electrical charge balance to measurement data from A. calcoaceticus cultures. Comparison of the published biomass yield data and the calculated rate of lactone hydrolysis revealed that they do not quantitatively agree. It can be concluded that the observed relation between biomass yield and lactone hydrolysis is only apparent. The results demonstrate the power of the electrical charge balance in the study of processes in which charged compounds are being converted.
Recombinant Human Insulin
Authors: Ladisch Michael R. , Kohlmann Karen L. 
Published: March 2005

AbstractInsulin is a well‐characterized peptide that can be produced by recombinant DNA technology for human therapeutic use. A brief overview of insulin production from both traditional mammalian pancreatic extraction and recombinant bacterial and yeast systems is presented, and detection techniques, including electrophoresis, are reviewed. Analytical systems for insulin separation are principally based on reversed‐phase chromatography, which resolves the deamidation product(s) (desamido insulin) of insulin, proinsulin, and insulin. Process‐scale separation is a multistep process and includes ion exchange, reversed‐phase, and size exclusion chromatography. Advantages and/or disadvantages of various separation approaches, as described by the numerous literature references on insulin purification, are presented.
Effects of Glucose Fluctuations on Synchrony in Fed‐Batch Fermentation of Saccharomyces cerevisiae
Authors: Namdev Pradyumna K. , Thompson B. G. , Ward Dennis B. , Gray Murray R. 
Published: March 2005

AbstractThe effects of transient conditions, due to fed‐batch dynamics and fluctuations in glucose supply, on synchronous growth were evaluated by conducting fed‐batch fermentation of Saccharomyces cerevisiae. Chemostat operation with dilution rates of 0.2 and 0.1 h−1 produced periodic oscillations of the CO2 fraction in off‐gas and of the budded fraction of the cell population. A fed‐batch operation with an exponentially increasing glucose feed was started from a synchronized culture established in a chemostat. The CO2 cycles continued for about five cycles (11 h of feed time) and then they disappeared due to gradual decay of synchrony. The fluctuations in glucose supply due to poor mixing were simulated by an intermittent supply of nutrients with a pulse‐on time of 5 s and a pulse‐off time varying from 3 to 39 s according to Monte Carlo method. Such rapid fluctuations in glucose supply during a fed‐batch fermentation immediately produced a chaotic response in CO2 levels which indicated a complete disruption of the synchrony established previously in a chemostat. The elimination of CO2 oscillations was consistent with the measurements of the fraction of budded cells. These results suggest that synchrony cannot be established in large‐scale stirred fermentors due to inherent concentration gradients.
Concentrating Cellulases from Fermented Broth Using a Temperature‐Sensitive Hydrogel
Authors: Park Chang‐Ho , Orozco‐Avila Ignacio 
Published: March 2005

AbstractA temperature‐sensitive poly(N‐isopropylacrylamide) hydrogel was used to concentrate cellulases from the fermentation broth of Trichoderma reesei. The steady‐state gel volume was less and the gel collapse temperature was lower in fermented broth compared to those in water. Upon a long (24 h) temperature swing for gel swelling, a gel with lower monomer and cross‐linker content showed a larger volume increase, and it took longer to reach a constant volume which was smaller than the steady‐state volume. Upon a long (24 h) temperature swing for gel collapsing, different gels reached the same collapsed volume in a short period of time. The largest volume increase per unit temperature decrease was obtained for a temperature swing between 28 and 33 °C. For short temperature swings (1–5 h), swollen and collapsed gel volumes were reproducible and were approximately the same as the final volumes during long (24 h) swings. Separation efficiency was higher for the gel with a smaller volume change because of higher concentrations of monomer or cross‐linking agent. When the gels were reused, separation efficiency was improved.
Biomimetic Metal‐Sorbing Vesicles: Cd2+ Uptake by Phosphatidylcholine Vesicles Doped with Ionophore A23187
Authors: Van Zanten John H. , Monbouquette Harold G. 
Published: March 2005

AbstractUnilamellar phosphatidylcholine vesicles, harboring the ionophore, A23187, in the bilayer and the water‐soluble chelating agent, nitrilotriacetate, in the vesicle interior, rapidly sequester and concentrate Cd2+ from dilute aqueous solution. Metal‐sorbing vesicle permeabilities for cadmium ion at 5 ppm (42.8 μM) ranged from 8.09 × 10−7 to 1.27 × 10−4 cm/s for surface A23187 concentrations of 0.22–2.27 pmol/cm2 (which correspond to lipid: carrier molar ratios of 2000:1 to 200:1) and pH's from 5.5 to 8.5. The Cd2+ permeability shows linear variation with carrier concentration under the conditions studied. As pH is decreased, an increasing fraction of the A23187 becomes protonated, and the permeability exhibits a positive linear relationship with a function related to that for the fraction of unprotonated carrier. These noncovalently assembled, metal‐sorbing vesicles exhibit shelf lives of several months and remain stable throughout typical metal sorption studies.
NMR and Microelectrode Studies of Hydrodynamics and Kinetics in Biofilms
Authors: Lewandowski Zbigniew , Altobelli Stephen A. , Fukushima Eiichi 
Published: March 2005

AbstractProfiles of flow velocity and dissolved oxygen concentration were studied by NMR and microelectrodes near mixed population biofilms growing on polycarbonate substratum. The profile of dissolved oxygen concentration within the diffusion boundary layer and profiles of flow velocity within the hydrodynamic boundary layer can be described by exponential equations.
A Microwave Oven with Variable Continuous Power and a Feedback Temperature Controller
Authors: Tong C. H. , Lentz R. R. , Lund D. B. 
Published: March 2005

AbstractThe power supply circuit of a domestic microwave oven was modified so that the field intensity in the cavity could be changed continuously. The oven was further fitted with a feedback temperature controller for controlling product temperatures during microwave heating by cycling the magnetron on and off. The temperature controller consists of a fiber optic temperature sensing system, a computer, an optocoupler, and a mechanical relay. White bread, moist sponges, and a 5‐mL water load were used to test the performance of the oven. The temperature control capability was greatly influenced by the field intensity of the cavity and less influenced by the data acquisition rate. Experimental data indicated that it was possible to maintain the sample temperature within ±0.3°C at 60°C and within ±0.6 °C at 80°C when a proper power level was used.
Growth, Nutrient Consumption, and End‐Product Accumulation in Sf‐9 and BTI‐EAA Insect Cell Cultures: Insights into Growth Limitation and Metabolism
Authors: Bédard Charles , Tom Rosanne , Kamen Amine 
Published: March 2005

AbstractGrowth, nutrient consumption, and end‐product accumulation were quantitated in shake‐flask cultures of two insect cell lines, Sf‐9 and BTI‐EAA, in three different serum‐supplemented media. Per cell consumption or production rates were calculated for most medium components analyzed. Glucose was growth‐limiting in TNM‐FH medium and was the most important single source of organic‐C for the cells in all cultures. Cells utilized fructose and maltose but not sucrose. α‐Ketoglutarate and malate contributed significantly to the carbon budget of cells in TNM‐FH. Lactate generally did not accumulate during growth. Most of the amino acids were consumed by the cells, with the exception of alanine which was produced. Most of the amino acids appeared to be present in adequate supply in the cultures. Glutamate was generally the most rapidly consumed of the amino acids, followed closely by glutamine. Alanine accumulation was correlated with glucose consumption. In Sf‐9 cultures, ammonia accumulated only slightly or not at all as long as glucose was present in the medium, and uric acid was detectable at the end of growth and in the stationary phase. Added ammonia up to a concentration of 10 mM did not affect the growth of either cell line. Ammonia and lactate may be of less importance in limiting growth in insect cell cultures than in mammalian cell cultures. A hypothetical outline of the major metabolic pathways of the cultured insect cells is presented on the basis of information obtained here and in the literature.