bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular esterification by lipase powder in microaqueous benzene: Factors affecting activity of pure enzyme
Authors: Yamane Tsuneo , Ichiryu Takayuki , Nagata Masahiro , Ueno Asayo , Shimizu Shoichi 
Published: December 2004

AbstractVarious factors affecting the catalytic activity of pure lipase of Pseudomonas fluorescens in microaqueous benzene were investigated with respect to lactonization of 15‐hydroxypentadecanoic acid. Without deposition of the enzyme or of the enzyme plus activity enhancer (additive) on celite powder, the pure enzyme was very poorly dispersed in the microaqueous benzene, resulting in very low activity. The enzyme immobilized on celite powder exhibited the highest activity at a free water content of ca. 0.083%. When a sugar alcohol such as erythritol, arabitol, or sorbitol was added before lyophilization with approximate proportion of 3 g/g enzyme, marked increases in the enzyme activity were observed at a shifted optimal free water content, i.e., 0.04%. Inclusion of phosphotidylcholine resulted in a somewhat higher activity than in the system of enzyme plus celite only. Addition of lactose, bovine serum albumin, casein, dextran, polyvinyl alcohol, phosphate, or NaCl all caused a decrease in the enzyme activity. From the effects of the additives examined, it is deduced that the following three factors are required for a pure enzyme to exhibit its full activity in a water‐immiscible organic solvent: (1) optimum moisture content, (2) disperser (support particles having enough surface area on which the enzyme is thinly deposited), and (3) activity enhancer (additive) at optimum concentration The importance of noting the purity of the enzyme preparation is emphasized when its catalysis in an organic solvent is investigated.
Computer‐aided synthesis of biochemical pathways
Authors: Mavrovouniotis Michael L. , Stephanopoulos George , Stephanopoulos Gregory 
Published: December 2004

AbstractThe synthesis of biochemical pathways satisfying stoichiometric constraints is discussed. Stoichiometric constraints arise primarily from designating compounds as required or allowed reactants, and required or allowed products of the pathways; they also arise from similar restrictions on intermediate metabolites and bioreactions participating in the pathways. An algorithm for the complete and correct solution of the problem is presented; the algorithm satisfies each constraint by recursively transforming a base‐set of pathways. The algorithm is applied to the problem of lysine synthesis from glucose and ammonia. In addition to the established synthesis routes, the algorithm constructs several alternative pathways that bypass key enzymes, such as malate dehydrogenase and pyruvate dehydrogenase. Apart from the construction of pathways with desired characteristics, the systematic synthesis of pathways can also uncover fundamental constraints in a particular problem, by demonstrating that no pathways exist to meet certain sets of specifications. In the case of lysine, the algorithm shows that oxaloacetate is a necessary intermediate in all pathways leading to lysine from glucose, and that the yield of lysine over glucose cannot exceed 67% in the absence of enzymatic recovery of carbon dioxide.
Crossflow microfiltration of animal cells
Authors: Maiorella Brian , Dorin Glenn , Carion Antonio , Harano David 
Published: December 2004

AbstractLaminar shear is the primary mechanism of cell damage, limiting flow rate (and hence flux) in crossflow microfiltration of animal cells. Sensitivity to hydrodynamic and interfacial stress is reduced by the addition of 0.1% Pluronic polyol. A critical average wall shear rate of 3000 s−1 (above which damage occurs) is found for several cell types, including mammalian and insect cells. Hydrodynamic stress also limits the maximum tip speed in a rotary lobe pump to less than 350 cm/s. Turbulent flow in the recirculation loop piping at Reynolds numbers of up to 71,000 does not cause cell damage. Maximum sustainable flux decreases with cell concentration and increases with cell size (in qualitative agreement with the hydrodynamic lift model). A flux of 30 to 75 L/m2 h (depending on cell size) can be sustained during 20‐fold concentration from 2.5 × 106 cells/ml, while maintaining high cell viability.
Uptake of cadmium and zinc by the algaChlorella vulgaris: II. Multi‐ion situation
Authors: Ting Y. P. , Prince I.G. , Lawson F. 
Published: December 2004

AbstractMany microorganisms are capable of sequestering and concentrating heavy metals from their aqueous environment. While much research has beep carried out on the uptake of single species of metal ions, little attention seems to have been given to the study of multimetal ion systems. A mathematical model has previously been developed to describe the uptake of individual metal species by a microorganism. The model proposes two sequential processes: an initial rapid uptake due to cellular surface adsorption and a subsequent slow uptake due to membrane transport of the metal into the cells. This article extends the treatment by considering the uptake of two metal species together, cadmium and zinc, under different experimental conditions. The results are discussed in terms of possible mechanistic interactions.
In situ recalibration of probes of dissolved gas concentrations in bioreactors without effect on metabolism and growth
Authors: Iversen J. J. Lønsmann 
Published: December 2004

AbstractThis article describes a general method for the in situ recalibration of a probe for dissolved gas concentrations without changing any parameter but the gas composition. Recalibration of an oxygen probe is used as an example.The recalibration procedure can be used for any probe, provided the culture's rate of metabolism and growth is independent of the substrate concentration in the range being measured by the probe during recalibration. The method was tested using a galvanic oxygen electrode in an oxygen‐consuming culture of Klebsiella oxytoca and an oxygen‐evolving culture of Anabaena variabilis. The recalibration caused no detectable effect on the metabolism and growth of the cultures, provided the dissolved oxygen tension was above 3μM.
Growth and fermentation characteristics of new selected strains of Saccharomyces at high temperatures and high cell densities
Authors: Laluce Cecilia , Palmieri Mauricio Cesar , Lopes da Cruz Rose Cristina 
Published: December 2004

AbstractMaintenance of high cell viability was the main characteristic of our new strains of thermotolerant Saccharomyces. Total sugar conversion to ethanol was observed for sugarcane juice fermentation at 38–40°C in less than 10 h and without continuous aeration of the culture. Invertase activity differed among the selected strains and increased during fermentation but was not dependent on cell viability. Invertase activity of the cells and optimum temperature for growth, as well as velocity of ethanol formation, were dependent on medium composition and the type of strain used. At high sugarcane syrup concentrations, the best temperature for ethanol formation by strain 781 was 35°C. Distinct differences among the velocities of ethanol production using selected strains were also observed in sugarcane syrup at 35–38°C.
Fermentation of lactose to ethanol with recombinant yeast in an immobilized yeast membrane bioreactor
Authors: Jeong Yong S. , Vieth W. R. , Matsuura T. 
Published: December 2004

AbstractA novel concept of membrane bioreactor in which living cells are sandwiched between ultrafiltration (UF) and reverse osmosis (RO) membranes was applied for lactose fermentation to ethanol by genetically engineered yeast cells. The productivity of the Lactophile 13B strains was higher than that of the Lactophile 13D strains. In both cases performance data similar to those for glucose fermentation to ethanol by Saccharomyces cerevisiae were obtained. However, the operational stability of recombinant yeast cells was improved in the new bioreactor in comparison to the stability of these cells in a shake flask.
A study of the energetics and economics of microalgal mass culture with the marine chlorophyte Tetraselmis suecica: Implications for use of power plant stack gases
Authors: Laws E.A. , Berning J.L. 
Published: December 2004

AbstractThe marine phytoplankter Tetraselmis suecica was grown in shallow outdoor flumes for a period of approximately 6 months at the Natural Energy Laboratory of Hawaii. In full sunlight, gross production rates were 15–20 g C m−2 d−1. The corresponding photosynthetic efficiencies (PE's) were 9–10%. Respiration losses removed about half the gross production. The CO2 utilization efficiencies of 96 ± 11% were achieved by bubbling CO2 into the culture with the use of a counterflow sump system. Adding the CO2 in the form of carbonated water resulted in utilization efficiencies of 81 ± 11%. Archimedes screws proved superior to both paddle wheels and propellers as a means of circulating the water in the flumes. Insertion of foil arrays into the flumes to effect systematic mixing of the culture significantly enhanced production. The enhancement was greater when the foils were oriented at a small angle relative to the horizontal than when they were oriented at the same angle relative to the vertical. Light modulation effects are implicated as the probable cause of most of the enhancement. Substitution of electric power plant stack gases for pure CO2 resulted in no significant change in the production of T. suecica grown in chemostat culture.
Microfluorimetric analysis of spatial and temporal patterns of immobilized cell growth
Authors: Kuhn Robert H. , Peretti Steven W. , Ollis David F. 
Published: December 2004

AbstractPronounced spatial nonuniformities in cell density, physiology, and activity frequently arise within densely packed immobilized cell supports. For a more fundamental understanding of immobilized cell phenomena, we have developed high‐resolution microfluorimetric procedures to analyze local variations in both immobilized cell loading and growth rate. Fluorescent staining of total cellular DNA provides a measure of local biomass density. Actively growing (DNA synthesizing) cells are marked by pulse‐labeling newly synthesized DNA with the thymine analog, bromouracil. An immunofluorescent technique allows subsequent detection of spatial variations in DNA synthesis rates. These procedures enable the influence of mass‐transfer limitations and other immobilization effects on cell distribution and activity to be readily quantified. We demonstrate this approach through analysis of the patterns of growth of Escherichia coli entrapped within Sr‐alginate gel beads. The experimental techniques are potentially applicable to a variety of other aggregate cell systems.
Industrial scale harvest of proteins from mammalian cell culture by tangential flow filtration
Authors: van Reis Robert , Leonard Lee C. , Hsu Chung C. , Builder Stuart E. 
Published: December 2004

AbstractAn industrial‐scale methods for harvest of biologically active proteins form mammalian cell culture has been developed using tangential flow filtration. A robust and economical process capable of processing approximately 5000 L conditioned media/h with protein yields in excess of 99% has been achieved. A completely contained system has been designed in which total cell number and viability are maintained throughout the process. The process has successfully been implemented at 1.25 × 104 L scale for the recovery of kilogram quantities of pharmaceutical proteins such as recombinant tissue type plasminogen activator (rt‐PA).
Batch cultivation of Methylosinus trichosporium OB3b. I: Production of soluble methane monooxygenase
Authors: Park Sunghoon , Hanna Leslie , Taylor Robert T. , Droege Michael W. 
Published: December 2004

AbstractMethanotrophs have promising applications in bioremediation and in the production of fuel‐related chemicals due to their nonspecific enzyme, methane monooxygenase (MMO). The optimal conditions for cell growth and production of the soluble from of MMO (sMMO) were determined from batch cultivations of an obligatory methanotrophs, Methylosinus trichosporium OB3b, in shake flasks and a 5‐L bioreactor. It was confirmed that a copper deficiency is essential for the formation of the cytoplasmic sMNO. Optimum cell growth without added copper was observed at pH 6.0–7.0, temperature of 30–34°C, and phosphate concentration of 10–40 mM. In the bioreactor experiments, external CO2 addition eliminated the long lag period observed in the absence of added CuSO4, i.e., prior to the exponential cell growth phase. When methane was continuously supplied, the profile of the cell growth showed two different phases depending on the availability of nitrate, an initial fast exponential growth phase (specific growth rate, μ = 0.08 h−1) and a later slow growth phase (μ = 0.008 h−1). The cell density at the transition from a fast to a slow growth rate was proportional to the initial medium nitrate concentration in the range 5–20 mM and cell yield was estimated to be 7.14 g dry cell wt/g N. Whole‐cell sMNO activity remained essentially constant regardless of the growth rate unit cell growth stopped. With an initial medium iron concentration below 40 mM, an abrupt decrease in sMNO activity was observed. The lower sMNO activity could be restored by supplying additional iron to the bioreactor culture. Cell yield on iron was estimated to be 1.3 × 103 g dry cell wt/g Fe.
Proliferation of anchorage‐dependent contact‐inhibited cells: I. Development of theoretical models based on cellular automata
Authors: Zygourakis K. , Bizios R. , Markenscoff P. 
Published: December 2004

AbstractWe report the development of new class of discrete models that can accurately describe the contact‐inhibited proliferation of anchorage‐dependent cells. The models are based on cellular automata, and they quantitatively account for contact inhibition phenomena occurring during all stages of the proliferation process: (a) the initial stage of “exponential” growth of cells without contact inhibition; (b) the second stage where cell colonies form and grow with few colony mergings; and (c) the final stage where proliferation rates are dominated by colony merging events. Model prediction are presented and analyzed to study the complicated dynamics of large cell populations and determine how the initial spatial cell distribution, the seeding density, and the geometry of the growth surface affect the observed proliferation rates. Finally, we present a model variant that can simulate contact‐inhibited proliferation of asynchronous cell populations with arbitrary cell cycle–time distribution. The latter model can also compute the percentage of cells that are in a specific phase of their division cycle at a given time.
Proliferation of anchorage‐dependent contact‐inhibited cells. II: Experimental results and validation of the theoretical models
Authors: Zygourakis K. , Markenscoff P. , Bizios R. 
Published: December 2004

AbstractThis study establishes that the cellular automata models developed in an earlier article capture the essential features of the proliferation process for anchorage‐dependent contact‐inhibited cells. Model predictions are in excellent agreement with experimental data obtained with bovine pulmonary artery endothelial cells. The models are particularly suitable for predictive purposes since they have no adjustable parameters. All model parameters can be easily obtained from a priori measurements. Our studies also show that proliferation rates are very sensitive to the spatial distributions of seed cells. The adverse effects of seeding heterogeneities become more pronounced as a cell population approaches confluency and they should be accounted for in experimental studies attempting to assess the response of cells to external stimuli.
Production of L‐phenylacetyl carbinol by biotransformation: Product and by‐product formation and activities of the key enzymes in wild‐type and ADH isoenzyme mutants of Saccharomyces cerevisiae
Authors: Nikolova P. , Ward O. P. 
Published: December 2004

AbstractThe capacities of yeast wild‐type and mutants strains known to lack specific ADH isoenzymes to produce L‐phenylacetyl carbinol (PAC) and benzyl alcohol in biotransformation trials were also investigated. Pyruvate decarboxylase activity, responsible for PAC formation and ADH activity, which can participate in reduction of benzaldehyde to benzyl alcohol, was also determined in each strain. In addition, the capacity of each strain to produce ethanol was investigated. Mutant strains lacking all of the isoenzymes, ADH‐I, ADH‐II, and ADH‐III, still exhibited some ADH activity and were capable of production of benzyl alcohol and ethanol.
Growth and stoichiometry of a Catharanthus roseus cell suspension culture grown under nitrogen‐limiting conditions
Authors: Rho Denis , André Gérald 
Published: December 2004

AbstractThe uptake of carbohydrate and nitrate by Catharanthus roseus cell suspension cultures was studied in relation to biomass production in shake flasks. Biomass production was similar when using either 6, 12, 18, or 24 mM nitrate as the nitrogen source and 20 g L−1 sucrose as the carbon source. In all cases, maximum biomass production was reached when carbohydrates were entirely consumer by the cells. Apparent biomass yields, YX/S and YX/N were 0.49 g biomass g−1 glucose equivalent and 0.23 g biomass mmol−1 nitrate, respectively. The determination of the cellular carbon‐to‐nitrogen ration (C/N ration) resulted in the identification of three district growth phases: an active growth phase, and accumulation phase, and a biomass decline phase (endogenous metabolism). The onset of the last two phases was correlated with nitrate and sugar of the last two phases was correlated with nitrate and sugar exhaustion, respectively. Balanced stoichiometric equations describing the active growth and accumulation phases were proposed based on elemental composition and ash content of the biomass. The stoichiometric equation related to the accumulation phase predicts that the available sugars are stored as starch‐ and lipid‐like materials.
On the thermodynamics of microbial growth processes
Authors: Sandler Stanley I. , Orbey Hassan 
Published: December 2004

AbstractIn this article, we provide a rigorous thermodynamic analysis of microbial growth process, clarify the role of the generalized degree of reduction concept as it is used in both stoichiometric equations and as a characterizing factor for thermophysical properties, and introduce a classification method to account for errors when using the generalized degree of reduction to estimate the energy and free energy contents of molecules. We maintain the advantages of using the generalized degree of reduction while correcting for the large errors in the principle of energy regularity, especially for small molecules and for nitrogen‐source compounds. As a result, we obtain more accurate energy balances (heat loads) and second law constraints, and are able to clarify contradictory statements in the literature as to whether nonphotosynthesis fermentation process can produce oxygen or absorb rather than produce heat. Indeed, the answers to such questions become evident using the classification system introduced here.
Kinetics of enzymatic hydrolysis of olive oil in biphasic organic‐aqueous systems
Authors: Tsai Shau‐Wei , Wu Guang‐Huei , Chiang Chen‐Li 
Published: December 2004

AbstractA theoretical model for the lipase‐catalyzed hydrolysis of high‐concentration olive in biphasic isooctane‐aqueous systems has been proposed and confirmed by experiments. The enzymatic reaction of the Michaelis‐Menten type that occurred at the interface between organic and aqueous phases was assumed in deriving the rate equations, from which the maximum reaction rate could be obtained by carefully adjusting the volume ratio between the two phases to the optimal value. Equilibrium conversions higher than 98% for 0.1 g/L olive oil in isooctane were attained for systems with volume ratios up to one. Fractions of lipase and lipase‐substrate complex adsorbed at the interface increased and seemed to approach to asymptotic values asthe rotation speed of impeller increased. Activity of the lipase showed no apparent change between 26 and 37°C, but decrease rapidly with temperature above 43°C. The methodology presented in this work might be used to find kinetic parameters for reactor design and scaleup.
Optimization of a two‐stage recombinant fermentation process: The dilution rate effect
Authors: Hortacsu Amable , Ryu Dewey D. Y. 
Published: December 2004

AbstractThe effects of dilution rates on the performance of a two‐stage fermentation system for a recombinant Escherichia coli culture were studied. Dilution rate determines the apparent or averaged specific growth rate of a heterogeneous population of cells in the recombinant culture. The specific growht rate affects the genetic parameters involved in product formation in the second stage, such as plasmid stability, plasmid content, and specific gene expression rate. Kinetic models and correlations were developed for these parameters based on experimental data. Simulations of plasmid stability in the first stage showed that for longer fermentation periods, plasmid stability is better at higher dilution rates. However, the plasmid content is lower at these dilution rates. The optimal apparent specific growth rate for maximum productivity in the second stage was determined using two methods: (1) direct search for a constant specific growth rate, and (2) dynamic optimization using the maximum principle for a time‐dependent specific growth rate profile. The results of the calculations showed that the optimum constant apparent specific growth rate for maximum over‐all productivity is 0.40 h−1. This coincides with the optimal specific growht rate for maximum plasmid content in the expressed stage. A 3.5% increase in overall productivity can be obtained by using a linear time dependent apparent specific growth rate control, μ2(t) = 0.0007t, in the course of the fermentation time.
Xylanase production by Aspergillus awamori. Development of a medium and optimization of the fermentation parameters for the production of extracellular xylanase and β‐xylosidase while maintaining low protease production
Authors: Smith David C. , Wood Thomas M. 
Published: December 2004

AbstractA growth medium was developed for maximal production in batch culture of extracellular xylanase and β‐xylosidase by Aspergillus awamori CMI 142717 and a mutant (AANTG 43) derived from the wild‐type strain. The optimum pH for the production of xylanase and β‐xylosidase was 4.0. The best temperature of xylanase production was 30°C; 35°C was optimal for β‐xylosidase. Protease production was never completely suppressed under any of the conditions tested. However, protease titre was 3.5‐fold less than the control in medium in which proteose peptone and yeast extract were omitted: the level of xylanase was not affected (8.6 U mL−1) but β‐xylosidase titre was increased 4.7‐fold to 1.5 U mL−1. When corn steep liquor was used as the sole nitrogen source, xylanse and β‐xylosidase titres were further increased by 1.5‐ and 1.9‐fold, respectively. Of the carbon sources investigated, ball‐milled oat straw or oat spelt xylan produced the highest titres of xylanse and β‐xylosidase. None of the soluble carbon sources investigated produced the high titres of xylanase or β‐xylosidase induced by either oat straw for xylanse and β‐xylosidase was 2% and the optimum spore inoculum was between 106 and 107 spores/mL−1 final concentration. The level of xylanse activity obtained in the culture filtrates of the mutant was a remarkable 820 U mL−1 when the reducing sugar released was measured by the dinitrosalicylic acid method. This enzyme titre would appear to be the highest reported so far. The xylanases system contained the correct balance of enzymes to effect extensive hydrolysis of oat spelt xylan. The protease titre was very low.