bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermostability of alcohol dehydrogenase: Evidence for distinct subunits with different deactivation properties
Authors: Skerker Paul S. , Clark Douglas S. 
Published: December 2004

AbstractSeveral independent experimental techniques, including nondenaturing and denaturing isoelectric focusing, spin labeling, and enzyme immobilization, indicate that four ethanol‐active subunits of horse liver alcohol dehydrogenase (LADH) can be classified as one of two types, designated E1 and E2. Thermal inactivation studies of LADH in solution and immobilized to two different supports demonstrate that the first‐order rate constants of deactivation of E1 and E2 differ by more than an order of magnitude. Furthermore, E1, and E 2 can be distinguished by EPR spectroscopy, with the less stable subunit type, E2, appearing to have the less compactly structured active‐site environment. The less stable enzyme form also loses catalytic activity upon covalent attachment to CNBr‐Sepharose but remains active when adsorbed to Octyl‐Sepharose. Moreover, the immobilization results in conjunction with lysine modification studies suggest that E2 immobilized to CNBr‐Sepharose cannot bind coenyzme. Overall, these results illustrate how EPR measurements in concert with activity assays can pro vide insights into the molecular mechanisms of enzyme stabilization.
Mathematical modeling of growth and production of alcohol oxidase by Hansenula polymorpha grown on methanol–glucose mixtures
Authors: Giuseppin M. L. F. 
Published: December 2004

AbstractThe modeling of growth and production of methanol oxidase (MOX) by Hansenula polymorpha CBS 4732 has been studied to provide a mathematical description of such production processes. Two kinds of mathematical models were constructed for growth on methanol and on mixtures of methanol and glucose. The model for growth on methanol as the sole carbon source consists of kinetics expressions, a limited number of key steps incorporating substrate and production inhibition. This model was used to predict and simulate the culture dynamics at the start‐up, the most critical step in continuous cultivation. The growth on mixtures of methanol and glucose was modeled assuming virtually independent metabolic pathways. The induction and production of MOX could be described by adaptation of various repression equations for various data from the literature. The models describe both experimental data and literature data on growth of H. polymorpha CBS 4732 on glucose–methanol mixtures satisfactorily. All parameters for the induction–repression model for growth of H. polymorpha CBS 4732 on glucose–methanol mixtures yielded evidence that a similar induction–repression pattern is involved in MOX production. Catalase, however, is repressed by a different mechanism.
Recycle use of immobilized glucoamylase by tangential flow filtration unit
Authors: Uttapap Dudsadee , Koba Yojiro , Ishizaki Ayaaki 
Published: December 2004

AbstractVarious properties of glucoamylase immobilized onto corn stover supporting material and separation of immobilized enzyme by tangential flow filtration unit were studied. Optimum pH and temperature of immobilized enzyme were 3.5 and 60°C, respectively. Enzyme stability was studied in a packed‐bed column. The starch conversion rate was attained at 81% for 15 days; after that, the hydrolysis rate gradually decreased. Size of supporting material proved to be an important factor, with higher activity and good loading yield resulting from smaller supporting material. Glucoamylase immobilized onto supporting material less than 44 μm was used for hydrolysis of 10% soluble starch at pH 3.5 and 40°C for 3 h. Then immobilized glucoamylase was separated from the product by means of a tangential flow filtration unit using a 0.2‐μm pore size Nylon 66 membrane filter. This operation was continued until 180 ml filtrate was obtained from a 260‐mL starting volume. Then, the next batch was started by adding 180 mL starch substrate into the reactor. The batchwise experiments were repeated 20 times. The average filtration rate of each batch was determined and found to sharply decline during the first four batches. Thereafter, it gradually decreased from batch to batch. The cause of decreasing filtration rate appeared to be due to retrogradation of starch. The percentage of starch hydrolysis within 20 batches was in the range 89–96%. The filtration rate becomes higher if the hydrolyzation time is extended to 14 h. Resistance to filtration was also investigated. Almost all of the total resistance is related to insoluble materials, with the significant part of this from the resistance due to insoluble materials deposited on a surface of membrane and boundary layer resistance. Using a microscopic method, no microorganisms were found in the filtrate.
Drag reducing properties of microalgal exopolymers
Authors: Ramus J. , Kenney B. E. , Shaughnessy E. J. 
Published: December 2004

AbstractDilute aqueous solutions of polymers released by marine phytoplankton (microalgae) were shown to effectively reduce drag in capillary pipe flow. Tests were performed in a capillary turbulent flow viscometer which extruded small samples under high pressures. In all, 22 species were screened, and the products of one chlorophyte and four rhodophyte species proved especially effective. The viscoelastic polymers produced by these species delayed the transition from laminar to turbulent flow to significantly higher Re. In general, polymeric regime segments come off the maximum drag reduction asymptote at characteristic retro‐onset points, and come to lie approximately parallel to, but displaced upwards from the Prandtl–von Karman line. The delay to transition was shown to be dependent on additive polymer concentration, capillary diameter, and temperature. Ionic concentration, ionic composition, or pH had little effect on drag reducing properties.
Liquid residence time distributions in immobilized cell bioreactors
Authors: Swaine Donald E. , Daugulis Andrew J. 
Published: December 2004

AbstractPrevious work has demonstrated that high ethanol productivities can be achieved using yeast or bacterial cells adsorbed onto the surface of ion exchange resin in vertical packed bed bioreactors. The present work quantitatively characterizes the overall degree of backmixing in such reactors at two scales of operation: 2.0 and 8.0 L. Stimulus‐response experiments, using two solvents (2,3‐butanediol and 2‐ethoxyethanol) as tracers, were performed to measure the liquid phase residence time distribution (RTD) during continuous ethanol fermentations using the yeast Saccharomyces cerevisiae and the bacterium Zymomonas mobilis at the 2‐L scale, and with S. cerevisiae at the 8‐L scale. In order to separately determine the effects of liquid flow rate and gas evolution on the degree of mixing, stimulus–response experiments were also performed in the systems without microbial cells present. The evolution of CO2 was found to dramatically increase the extent of mixing; however, the tanks‐in‐series model for non‐ideal flow represented the systems adequately. The packed beds were equivalent to over 70 tanks‐in‐series during abiotic operation while during fermentations, with similar liquid flow rates, they ranged in equivalence from 35 to 15 tanks‐in‐series. This increased knowledge of the overall degree of mixing in packed bed, immobilized cell bioreactors will allow for more accurate kinetic modelling and efficient scale up of the process.
Fermentation data analysis and state estimation in the presence of incomplete mass balance
Authors: Liao James C. 
Published: December 2004

AbstractA method is developed for identifying measurement errors and estimating fermentation states in the presence of unidentified reactant or product. Unlike conventional approaches using elemental balances, this method employs an empirically determined basis, which can tolerate unidentified reaction species. The essence of this approach is derived from the concept of reaction subspace and the technique of singular value decomposition. It is shown that the subspace determined via singular value decomposition of multiple experimental data provides an empirical basis for identifying measurement errors. The same approach is applied to fermentation state estimation. Via the formulation of the reaction subspace, the sensitivity of state estimates to measurement errors is quantified in terms of a dimensionless quantity, maximum error gain (MEG). It is shown that using the empirically determined subspace, one can circumvent the problem of unidentified reaction species, meanwhile reducing the sensitivity of the estimates.
Kinetics of whey–lactose acidogenesis
Authors: Kissalita W. S. , Lo K. V. , Pinder K. L. 
Published: December 2004

AbstractThe mixed‐culture anaerobic conversion of lactose to organic acids in a bench‐scale continuous‐flow stirredtank fermentor is considered. The major acidogenic end‐product distribution with respect to the dilution rate are presented. A Monod chemostat model is employed to describe a microbial growth, and the influence on pH of the estimated model parameters is discussed.
Plasmid maintenance and protein overproduction in selective recycle bioreactors
Authors: Ogden Kimberly L. , Davis Robert H. 
Published: December 2004

AbstractA new plasmid construct has been used in conjunction with selective recycle to successfully maintain otherwise unstable plasmid‐bearing E. coli cells in a continuous bioreactor and to produce significant amounts of the plasmid‐encoded protein β‐lactamase. The plasmid is constructed so that pilin expression, which leads to bacterial flocculation, is under control of the tac operon. The plasmid‐bearing cells are induced to flocculate in the separator, whereas cell growth and product synthesis occur in the main fermentation vessel without the inhibiting effects of pilin production. Selective recycle allows for the maintenance of the plasmid‐bearing cells by separating flocculent, plasmid‐bearing cells from nonflocculent, segregant cells in an inclined settler, and recycling only the plasmid‐bearing cells to the reactor. As a result, product expression levels are maintained that are more than ten times the level achieved without selective recycle. All experimental data agree well with theoretical predictions.
Ion exchange and affinity chromatography in the scaleup of the purification of α‐galactosidase from soybean seeds
Authors: Porter Jill E. , Ladisch Michael R. , Herrmann Klaus M. 
Published: December 2004

AbstractSoybeans (Glycine max) contain an α‐galactosidase that makes up a small fraction of the total protein of the seed. The properties of this enzyme are of interest because of its potential to convert the galactooligosaccharides, stachyose and raffinose, in soybean meal to sugars digestible in the human gastro intestinal tract and thereby increase potential uses of this vegetable protein source in human and animal foods. Study of this enzyme required the isolation of milligram quantities of electrophoretically pure protein from ground soybeans and therefore, scaleup of laboratory procedures by a factor of 300 times. Large scale acid precipitation, ammonium sulfate precipitation, and centrifugal recovery of the precipitated protein allowed α‐galactosidase to be isolated from 45.5 kg soybean meal containing 17.1 kg protein, to obtain an enzyme extract with a specific activity of 90 to 100. A novel combination of strong anion exchange and cation exchange chromatography followed by Concanavalin‐A affinity chromatography with a methyl α‐D mannoside gradient gave α‐galactosidase with an average specific activity of 56,000. Ion exchange chromatography preceding Concanavalin‐A affinity chromatography allowed elimination of a relatively costly melibiose affinity chromatography step (which followed the Concanavalin‐A column In the laboratory procedure) thereby making scaleup practical.
Enzymatic synthesis of a sucrose‐containing linear polyester in nearly anhydrous organic media
Authors: Patil Damodar R. , Rethwisch David G. , Dordick Jonathan S. 
Published: December 2004

AbstractA variety of enzymes have been found to acylate sucrose in anhydrous pyridine. The enzymic reaction is highly selective; with trifluoroethylbutyrate as ester donor, enzyme‐catalyzed transesterification of sucrose yielded sucrose 1′‐butyrate and sucrose 6, 1′‐dibutyrate. No sucrose–tributyrates were formed. Using a similar technique, a long‐chain linear sucrose polyester has been prepared using Proleather, an alkaline protease from a Bacillus sp. This protease catalyzes the esterification of sucrose with bis(2, 2, 2‐trifluoroethyladipate) in a 1:1 ratio to yield a sucrose‐containing polyester with Mw = 2100 and Mn = 1600 for a polydispersity of 1. 31. Polymers with molecular weights in excess of 13, 000 have been prepared by this enzymic approach, indicating that molecules containing over 30 sucrose units have been produced. The polyester is extremely water soluble and soluble in polar organic solvents. As with the sucrose dibutyrate, the polyester has ester linkages at the C6 and C1′ positions on the sucrose. The polyester can be depolymerized using Proleather in aqueous buffer, pH7. After 9 days in aqueous buffer, Proleather catalyzed the breakdown of the polyester to an Mw of ca. 900. This sucrose‐containing polyester may have applications as a water‐absorbent, biodegradable plastic for use as diapers and hygienic products, water‐treatment chemicals, and components of drug delivery systems.
Retention of enzyme by electropolymerized film: A new approach in developing a hypoxanthine biosensor
Authors: Nguyen An‐Lac , Luong John H. T. , Yacynych Alexander M. 
Published: December 2004

AbstractAn amperometric biosensor for hypoxanthine was constructed by forming a layer of crosslinked xanthine oxidase on a platinum electrode, followed by electropolymerization of a submonolayer film of resorcinol and para‐diaminobenzene. The fabricated electrodes were evaluated for speed of response, sensitivity, and reusability. Optimal performance was obtained with enzyme‐based electrodes sparsely covered with film which was formed by electropolymerization in less than 6 min. The resulting electrodes exhibited linear response to hypoxanthine in the. range 5–300 μM with a response time of 2 min. Application of the biosensor in monitoring hypoxanthine content of fish extracts yielded results which agreed well with spectrophotometric assays using soluble xanthine oxidase. The biosensor was stable for 60 days when stored at 4°C in phosphate buffer and it could be used continuously for 6 h with over 50 assays.
A fiber‐bed bioreactor for anchorage‐dependent animal cell cultures: Part I. Bioreactor design and operations
Authors: Chiou Tzyy‐Wen , Murakami Sei , Wang Daniel I. C. , Wu Wen‐Tung 
Published: December 2004

AbstractA concentric‐cylinder airlift reactor, in which the annulus is a packed bed of glass fibers, has been developed in order to facilitate the scaleup and enhance the volumetric productivity of anchorage‐dependent animal cell cultures. In this bio‐reactor, oxygen‐containing gas is sparged through the inner draft tube, causing bubble‐free medium to flow through the fiber bed in the outer cylinder and providing both oxygenation and convective nutrient transfer to the cells. Several other desirable features for reactor operation are also provided by this design. Cell cultivations in this bioreactor have been successfully carried out and provide data for the feasibility of the large‐scale cell cultivation.
A fiber‐bed bioreactor for anchorage‐dependent animal cell cultures: Part II. Scaleup potential
Authors: Murakami Sei , Chiou Tzyy‐Wen , Wang Daniel I. C. 
Published: December 2004

AbstractA simple hydrodynamic model is introduced to describe the airlift fiber‐bed bioreactor, which can enhance the volumetric productivity of anchorage‐dependent animal cell cultures. By applying the model, liquid flow rates and volumetric mass transfer coefficients are predicted and are in agreement with experimental measurements. Consequently, the optimal reactor configuration giving the maximal oxygen supply is derived. Also, theoretical scaleup potential of this concentric internal loop reactor is considered for volumes ranging from 10 to 67,000 L with which cell densities of 5.1 × 107 and 1.2 × 107 cells/cm3, respectively, can be maintained.
Enzymatic production of cyclodextrins from unliquefied corn starch in an attrition bioreactor
Authors: Lee Yun‐Dong , Kim Hak‐Sung 
Published: December 2004

AbstractA novel enzymatic process for the production of cyclodextrins from unliquefied starch was developed. Cyclodextrins were produced in an attrition bioreactor in which simultaneous hydrolysis of starch and synthesis of cyclodextrins by cyclodextrin glycosyltransferase (CGTase) occur. The CGTase was obtained from isolated Bacillus sp. BE101, and maximum activity of the enzyme was observed at pH 6.0 and a temperature of 45°C. The effect of milling media size and material on the performance of the attrition bioreactor was investigated, and operational parameters such as agitation speed, volume of milling media, ratio of enzyme to starch, and starch concentration were optimized. The production yield of cyclodextrins from unliquefied corn starch of 15% reached 35% at 24 h under optimized conditions. Energy consumption for the production of cyclodextrins in the attrition bioreactor system was estimated to be about 25% of that required for the liquefaction of starch in the conventional process.
Optimization of pro‐urokinase secretion from recombinant Saccharomyces cerevisiae
Authors: Turner Brian G. , Avgerinos George C. , Melnick Laurence M. , Moir Donald T. 
Published: December 2004

AbstractSecretion of a nonglycosylated form of human pro‐urokinase, also known as single‐chain urinary plasminogen activator (scu‐PA), from Saccharomyces cerevisiae is described. A “supersecreting” yeast strain harboring multiple copies of integrated plasmids was grown batchwise and at constant respiratory quotient (RQ) in 20‐L fermenters. Because the promoters used to drive expression of the pro‐urokinase genes are not tightly regulated, secretion into the culture supernatant was growth associated. Although the final cell density achieved in the perturbed‐batch fermentation (45 g dry wt/L) was less than that observed in the RQ‐controlled culture (77 g dry wt/L), the scu‐PA titer in the perturbed‐batch fermentation (1863 IU/mL) was nearly twice that attained at constant RQ (1108 IU/mL). The effects on cell growth and scu‐PA titer of other process variables (pH, temperature, phosphate concentration, and medium composition) are also discussed.
Structured modeling of a microbial system: I. A theoretical study of lactic acid fermentation
Authors: Nielsen Jens , Nikolajsen Karin , Villadsen John 
Published: December 2004

AbstractMost fermentation models presented in the literature are unstructured, i.e., the biomass composition is assumed constant during all operating conditions. These models are unable to simulate experiments carried out at widely different operating conditions. It is therefore interesting to examine simple structured models where knowledge of the cell physiology is taken into account in the modeling phase. In this article, a simple structured model is presented. The model is based on experimental work with the lactic acid bacteria Streptococcus cremoris, but due to the similarities in basic metabolism for many microorganisms it is applicable also for other fermentation system. The basic assumption in the model is that the biomass can be divided into two parts (compartments)–an active part and a mainly inactive structural part. The size of the active part has a pivotal role in the model.
Characterization of a pilot plant airlift tower loop bioreactor. I: Evaluation of the phase properties with model media
Authors: Fröhlich S. , Lotz M. , Korte T. , Lübbert A. , Schügerl K. , Seekamp M. 
Published: December 2004

AbstractInvestigations were carried out in a 9 m high, 4 m3 volume, pilot plant airlift tower loop bioreactor with a draft tube. The reactor was characterized by measuring residence time distributions of the gas phase using pseudostochastic tracer signals and a mass spectrometer and by evaluating the mixing in the liquid phase with single‐pulse tracer inputs. The local gas holdup and the bubble size (piercing length) were measured with two‐channel electrical conductivity probes. The mean residence times and the intensities of the axial mixing in the riser and downcomer and the circulation times of the phases as well as the fraction of the recirculated gas phase were evaluated. The gas holdup in the riser is nearly uniform along the reactor. In the downcomer, it diminishes from top to bottom. The liquid phase dispersion coefficients, DL, are smaller than those measured in the corresponding bubble columns. In the pilot plant with tap water the following relationship was found: DLr = cw; with c = 203.4; n = 0.5;DLr(cm2 s−1;) and WSG(cm s−1) where DLr is the longitudinal dispersion coefficient in the riser and WSG is the superficial gas velocity. The gas phase dispersion coefficients in the riser of the pilot plant, DGr, are also enlarged with increasing superficial gas velocity, WSG, however, no simple relationship exists. Parameter DGr is the highest in the presence of antifoam agents, intermediate in tap water, and the smallest in ethanol solution.
Dilution rate as a determinant of mycelial morphology in continuous culture
Authors: Wiebe Marilyn G. , Trinci Anthony P. J. 
Published: December 2004

AbstractThe morphology of mycelial fungi in liquid culture effects culture rheology and this in turn may affect product yield. It is therefore important to understand how environmental factors influence mycelial morphology and this paper describes the effect of dilution rate on two strains ofFusarium graminearum,the relatively sparsely branched parental strain (A3/5) and a relatively highly branched “colonial” variant (C106). At any given dilution rate, the concentration of mycelial fragments present at steady state of both strains remained approximately constant with time, suggesting that mycelial fragmentation occurred in a regular manner. However, for both strains fragment concentration decreased with increasing dilution rate. The strains had a similar morphology at a dilution rate of 0.07 h−1. The length of the hyphal growth unit of A3/5 increased with increase in dilution rate, while that of C106 decreased with increase in dilution rate. At all dilution rates, C106 produced up to ten times more macroconidia than A3/5.