bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of DNA dumbbells. IV. Preparation and melting of a DNA dumbbell with the 16 base‐pair sequence 5′G‐T‐A‐T‐C‐C‐C‐T‐C‐T‐G‐G‐A‐T‐A‐C3′ linked on the ends by dodecyl chains
Authors: Doktycz Mitchel J. , Paner Teodoro M. , Benight Albert S.
Published: December 2004

The preparation and melting of a 16 base‐pair duplex DNA linked on both ends by C12H24 (dodecyl) chains is described. Absorbance vs temperature curves (optical melting curves) were measured for the dodecyl‐linked molecule and the same duplex molecule linked on the ends instead by T4 loops. Optical melting curves of both molecules were measured in 25, 55, and 85 mM Na+ and revealed, regardless of [Na +], the duplex linked by dodecyl loops is more stable by at least 6°C than the same duplex linked by T4 loops. Experimental curves in each salt environment were analyzed in terms of the two‐state and multistate theoretical models. In the two‐state, or van't Hoff analysis, the melting transition is assumed to occur in an all‐or‐none manner. Thus, the only possible states accessible to the molecule throughout the melting transition are the completely intact duplex and the completely melted duplex or minicircle. In the multistate analysis no assumptions regarding the melting transition are required and the statistical occurrence of every possible partially melted state of the duplex is explicitly considered. Results of the analysis revealed the melting transitions of both the dodecyl‐linked molecule and the dumbbell with T4 end loops are essentially two state in 25 and 55 mM Na+. In contrast, significant deviations from two‐state behavior were observed in 85 m MNa+. From our previously published melting data of DNA dumbbells with Tn end loops where n = 2, 3, 4, 6, 8, 10, 14 [T. M. Paner, M. Amaratunga, and A. S. Benight, (1992) Biopolymers, Vol. 32, pp. 881–892] and the dumbbell with T4 end loops of this study, a plot of d(Tm)/d ln [Na+] was constructed. Extrapolation of this data to n = 1 intersects with the value of d (Tm)/d ln [Na+] obtained for the alkyl‐linked dumbbell, suggesting the salt‐dependent stability of the alkyl‐linked molecule behaves as though the duplex of this molecule were linked by end loops comprised of a single T residue. © 1993 John Wiley & Sons, Inc.
Biasing a Monte Carlo chain growth method with Ramachandran's plot: Application to twenty‐L‐alanine
Authors: Bascle J. , Garel T. , Orland H. , Velikson B.
Published: December 2004

In this paper, we explore the possibility of using experimental observations in the Monte Carlo chain growth method that we have previously developed. In this method, the macromolecule (peptide, protein, nucleic acid, etc.) is grown atom‐by‐atom (or residue‐by‐residue, etc.) and partial chains are replicated according to their Boltzmann weights. Once the molecule completed, we are left with a Boltzmann‐distributed ensemble of configurations. For long molecules, an efficient sampling of the (extremely large) phase space is difficult for obvious reasons (existence of many local minima, limited computer memory, etc.). In the case in which one is mainly interested in the low energy conformations, we have incorporated in the growth scheme experimental observations taken from the Protein Data Banks. More precisely, we have considered the case of twenty‐L‐alanine and we have used the (experimental) Ramachandran's plot for this residue. The biased growth procedure goes as follows: (a) each time one adds along the main backbone chain, either a carbon atom belonging to a carbonyl group, or a nitrogen atom, its dihedral angle (ϕ) or (ψ) is drawn with a probability law that reflects the experimental Ramachandran (ϕ,ψ) plot; (b) the bias introduced in this way is canceled through an extra term in the energy (replication energy = true energy + bias energy); (c) the configurations, generated at T = 1000 K, are then energy minimized. We have worked with an all‐atom CHARMM force field, and Ramachandran's plot for the alanine was modeled through three angular zones (α‐helix, β‐sheet, coil). In our calculations, the probabilities of the α (pα) and β (pβ) regions have been varied in large proportions (pα between 0.64 and 0.19, the “experimental” value being 0.59). The results, based on 35 “unbiased” and 25 “biased” (or “guided”) distinct minimized configurations clearly demonstrate the efficiency of the method. The low energy configurations, for all tested values of pα, have a total (or almost total) a helix content. The unbiased configurations have much higher energies (in general, even higher than the left‐handed helix). Note that the method is not “α helix in‐α helix out,” since working at T = 300 K with the experimental (pα = 0.59) value yields configurations partially frozen in a C alanine dipeptide type of local minima. © 1993 John Wiley & Sons, Inc.
Conformation and interactions of uteroglobin fragments 4–14 and 49–65 in aqueous solution containing surfactant micelles
Authors: Tessari Marco , Foffani Maria Teresa , Mammi Stefano , Peggion Evaristo
Published: December 2004

The conformation of two fragments of rabbit uteroglobin is described. The peptides are PRFAHVIENLL and PQTTRENIMKLTEKIVK, corresponding to helices I and IV in the crystal structure. CD shows that both peptides interact with sodium dodecyl sulfate (SDS) micelles and change their conformation to an α‐helix. The helical content estimated from the CD band at 222 nm is about 40% in each peptide. Surface tension measurements show that both peptides lower the critical micellar concentration (cmc) of SDS, with a more dramatic effect in the case of helix I. This peptide by itself acts as a surfactant, and is able to interact with SDS even below the observed cmc, forming β aggregates. Proton magnetic resonance (1H‐nmr) suggests that flexible helices are present. The longest helical stretches compatible with 1H‐nmr data extend from Phe6 to Leu14 for helix I and from Arg53 to Ile63 for helix IV. © 1993 John Wiley & Sons, Inc.
Bioactive peptides: Conformational studies of [TYR4] cyclolinopeptide A
Authors: Saviano Michele , Rossi Filomena , Filizola Marta , Isernia Carla , Di Blasio Benedetto , Benedetti Ettore , Pedone Carlo , Siemion Ignacy Z. , Pedyczak Artur
Published: December 2004

The solid state conformational analysis of [Tyr4] cyclolinopeptide A has been carried out by x‐ray diffraction studies. The crystal structure of the monoclinic form, grown from a dioxane‐water mixture [a = 9.849 (5) Å, b = 20.752 (4) Å, c = 16.728 (5) Å, β = 98.83 (3)°, space group P21, Z = 2], shows the presence of five intramolecular N‐H OC hydrogen bonds, with formation of one C17 ring structure, one α‐turn (C13), one inverse γ‐turn (C7), and two β‐turns (C10, one of type III and one of type 1). The Pro1‐Pro2 peptide unit is cis (ω = 5°) all others are trans. The structure is almost superimposable with that of cyclolinopeptide A. The rms deviation for the atoms of the backbones is on the average 0.33 Å. © 1995 John Wiley & Sons, Inc.
100 Years lock‐and‐key concept: Are peptide keys shaped and guided to their receptors by the target cell membrane?
Authors: Schwyzer Robert
Published: December 2004

The ideas developed in the Membrane Compartments Theory which allow a quantitative prediction of receptor preference are discussed in terms of our present knowledge of opioid and neurokinin receptor structure. Furthermore, conformations of regulatory peptides interacting with artificial lipid membranes are compared with those of chemically constrained molecules that react selectively with different receptor classes. Striking similarities in the topochemistry of molecules with similar activity were observed. The membrane‐induced topomers were almost congruent with the artificial topomers that are selectively recognized by the same receptors. © 1994 John Wiley & Sons, Inc.
Kinetics of 1‐dehydrogenation of steroids by Septomyxa affinis
Authors: Chen J. W. , Koepsell H. J. , Maxon W. D.
Published: December 2004

Mathematical models for the kinetics of 1‐dehydrogenation of steroids by Septomyxa affinis are considered. A model providing for product inhibition fits experimental data best. Product inhibition was also demonstrated directly.
Improved shaken flask performance
Authors: Gaden Elmer L.
Published: December 2004

Aeration in shaken flasks appears to take place primarily by absorption of oxygen in the thin film of fluid deposited on the flask walls. Marked improvement in aeration efficiency can be had by breaking up these films with an independent baffling surface. This improvement can be combined with an improved closure to give uniform and efficient shaken flask aeration.
A modified adsorption method for determining percentage of dead yeast cells
Authors: Vairo Marina L. R.
Published: December 2004

The adsorption of methylene blue from different aqueous solutions by dead yeast cells follows Freundlich's law when the percentage of dead cells varies from 0 to 100. When the Fink and Kühles methylene blue was used, there was observed a linear relation between the percentage of dead cells and the dye concentration at the equilibrium. The experimental errors were measured. A simpler and more precise colorimetric method for determining the percentage of dead yeast cells is deseribed.
The use of paper electrophoresis in studying the metabolism of pseudomonas species. I. Apparatus
Authors: Daniels William F. , Weaver R. H.
Published: December 2004

The sandwich paper electrophoresis technique, such as that of Foster (1952b), was modified to permit routine examination of as many as 15 samples of materials such as bacterial cultures, simultaneously, and with greater rapidity than with paper chromatography techniques. By the use of borate buffer at pH 9.6 with aniline hydrogen oxalate for development, materials such as glucose, fructose, 2‐ketogluconic acid, and 5‐ketogluconic acid could be separated in three hours.
Influence of the ionic concentration of nebulized suspensions on stability of microbial aerosols
Authors: Torloni Maurício
Published: December 2004

This paper shows that the ionic concentration of a cell suspension submitted to nebulization has a marked influence on the stability of the produced aerosol.
Stripping in sparged fermentation systems. I. Two component model systems
Authors: Hamer G.
Published: December 2004

A theoretical approach to the prediction of stripping or accumulation of minor components in solution with water by a sparged stream of dry air bubbles is developed and tested experimentally for two model systems, containing 1 mole‐% respectively, of ethanol, to represent situations where the minor component is more volatile than water, and of acetic acid, to represent the reverse. Close agreement between theory and practice is achieved in the former case, where an overall reduction in the liquid phase concentration of the minor component occurs, while in the latter, where overall accumulation occurs, there is some discrepancy. Considerations for an extension of the study are included.
Effect of potassium ferrocyanide on the chemical composition of molasses mash used in the citric acid fermentation
Authors: Clark D. S. , Ito K. , Tymchuk P.
Published: December 2004

The addition of potassium ferrocyanide to the molasses substrate (mash) used in the citric acid fermentation had little or no effect on the total carbon, nitrogen, or phosphorus content of the substrate but reduced the ash content by 1–4% depending on the type and crop year of molasses. Eighteen of the 21 metals identified in beet molasses by spectrographic analysis were precipitated in part by the treatment. The metals known to interfere with citric acid production, particularly manganese and iron, were those most efficiently precipitated. At mash temperatures of 80°C. and approximately 100°C., precipitation was completed within 15 min. after ferrocyanide addition and the reductions in the soluble mineral content in each case were similar. At 25°C. the precipitation reactions occurred but required more than 50 hr. to complete. Significantly more total mineral and more iron, calcium, and copper were precipitated at pHs 4 and 6 than at pH 8; manganese precipitation, however, was not affected by these pH changes.
Starter populations as determined under steady state conditions
Authors: Jannasch Holger W.
Published: December 2004

Continuous cultures of some heterotrophic Spirilli (Sp. serpens, Sp. curvatum, Sp. sp.) exhibit threshold concentrations of lactate, the growth limiting carbon and energy source, around 15 mg./l. This value corresponds to a threshold population density of 0.92 mg. dry weight/l. at a dilution rate of D = 0.185 hr.−1 (= 0.5 maximum growth rate). The minimum population density, which is regarded as equivalent to the starter population in batch culture, was dependent on the growth rate and the redox potential. The existence of minimum populations and the pronounced effect of population density on growth at low nutrient levels seem to be widespread phenomena closely related to growth under suboptimal conditions.
The motion of algae in turbulent flow
Authors: Powell C. K. , Chaddock J. B. , Dixon J. R.
Published: December 2004

Large cultures of microscopic, unicellular algae have been proposed as a means of maintaining a life‐supporting atmosphere in a closed, manned system. To achieve vigorous growth of the algal culture it is necessary to subject individual algae alternately to short periods of high intensity light and darkness. One of the means suggested for obtaining a favorable light–dark sequence for photosynthesis is to cause turbulence in a closed channel on which light is incident. Since light is rapidly attenuated in a dense suspension, there will be illuminated regions adjacent to the channel walls and a dark central core. The random motions of turbulence normal to the direction of flow would move the algae alternately from the illuminated regions to the dark region and back again. This paper indicates a method for analyzing the motion of algae into and out of the illuminated region of a channel formed by flat, parallel, transparent plates, with light incident on the plates. Matching of a probability model with a diffusion model makes it possible to estimate the light–dark sequence which could be achieved by turbulence. The results indicate that favorable sequences by this mechanism are unlikely.
Production of cell tissue from hydrocarbons by a microbiological process
Authors: Ertola R. J. , Lilly M. D. , Webb F. C.
Published: December 2004

Pseudomonas aeruginosa NCTC 5940 was grown in an aerated mineral salts medium with pure octadecane as sole carbon source, both in batch and continuous culture experiments. Carbon and nitrogen balances were made under different conditions. It was found that the only significant products were fresh cell tissue and carbon dioxide, although traces of several fatty acids were detected.
Toxin production by Clostridium tetani in biphasic liquid cultures
Authors: Puziss Milton , Hedén C.‐G.
Published: December 2004

An exploratory study is described on the use of a biphasic culture technique for production of toxin by C. tetani. The biphasic system used was a combination of dextran and poly(ethylene glycol) (PEG) in the presence of a protein‐free medium. The system supported good growth and gave a favorable phase ratio (top/bottom) of 15:1. The majority of the bacterial cells were in the bottom dextran phase, while the greater part of the toxin was in the upper PEG–medium phase. Toxin yields from a typical experiment were 109 mouse IP MLD/ml. of upper phase filtrate. The biphasic culture system was also adaptable to continuous culture, with approximately similar toxin levels found in the upper phase. The appearance of the clostridial cells in older cultures suggested the possibility of protoplast formation, perhaps stabilized by the polymers present. In vitro toxin titration (Lf) was inhibited by the presence of the polymers. Bacillus anthracis also grew well in the biphasic system and elaborated protective antigen, primarily into the upper phase.
The role of aeration and agitation in the production of glucose oxidase in submerged culture. II
Authors: Zetelaki Kornelia Z.
Published: December 2004

The main purpose of the work reported here was to establish the effectiveness of aeration and agitation, and to determine the best conditions of aeration for the growth and production of glucose oxidase of Aspergillus niger, on a semi‐industrial scale. Concentration of dissolved O2, O2 consumption and CO2 production were measured. It was found that the rate of growth and the activity of glucose oxidase per gram mycelium increased with the increase of speed of agitation. The concentration of dissolved oxygen of the fermentation broth, as well as the rate of respiration (O2 consumption and CO2 production) increased in direct proportion to the increase of speed of agitation, while assimilation of sugars was accelerated. The values of the respiratory ratio showed a fluctuation according to the presence or absence of sugar in the medium.
The relationship of oxidation‐reduction potential to the growth performance of tissue culture media poised prior to incubation
Authors: Daniels W. F. , Garcia L. H. , Rosensteel J. F.
Published: December 2004

Earlier observations revealed that incubation of media and the attendant changes in oxidation‐reduction potential (ORP) were related to improved cell production. This is a report, of work done to show that the higher levels and increased rates of growth of cells grown in incubated medium are associated with the ORP level of the medium before inoculation of the medium with cells. Work was done using 250‐ml centrifuge spinner bottles as the culture vessels. Further work is needed to establish the desirability of deliberate poising of media prior to use for studies in small vessels and flasks.
Glucose and lactic acid trends in suspension cultures of two established mammalian cell strains in chemically defined media
Authors: Bryant Jay C.
Published: December 2004

In replicated 30 to 40‐ml suspension cultures of rapidly proliferating monkey kidney cells of a comparatively fragile strain, the rates of glucose utilization and lactic acid accumulation averaged about 400 micrograms and 110 micrograms per 106 cells per day respectively, with average molar La/Gl ratios of 0.48. These two rates of glucose utilization and lactic acid accumulation were about 4 × and 10 × as high as the corresponding rates in comparable cultures of the hardier strain 2071‐L mouse fibroblasts under the same conditions, with average molar La/Gl ratios of 0.16. In comparable but nonproliferating suspension cultures of the same strain of monkey kidney cells, during about 3 weeks the rates were extremely high, with about 710 micrograms glucose utilized and 445 micrograms lactic acid accumulated per 106 cells per day, with average molar La/Gl ratios of 1.37. The rates of glucose uptake and lactic acid accumulation were higher in the nonproliferating cultures aerated with 5% CO2 in air than in those aerated with 10% CO2 in air. This difference was associated with pH, which was higher in the former group.

It was concluded that with this fragile strain of monkey Kidney cells(1) in nonproliferating cultures the cells were metabolizing actively but with a marked tendency to higher La/Gl ratios, (2) in the proliferating cultures the high rates of glucose utilization and lactic acid accumulation were definitely not directly correlated with the rate of growth, and (3) in none of the cultures was the amount of glucose remaining in the fluid at fluid changes so low as to have been a limiting factor.

Information in the literature concering glucose utilization and lactic acid production by cells vitro is voluminous and in some respects contradictory. In the present study the rates were unexpectedly high for the monkey kidney cells, particularly those in the otherwise apparently inactive nonproliferating cultures. The data seem to be unique, in that an established strain of cells in chemically defined medium in suspension cultures has been characterized for these metabolic parameters in both proliferating cultures and in equivalent nonproliferating cultures under directly comparable conditions.

The concept was developed that since these monkey kidney cells are obviously more fragile than the other cells examined, the complex physical stresses imposed upon these cells in agitated cultures can be modified and lessened in order to permit growth. Lessening of such mechanical stress waa brought about in several ways, of which only the smaller flask size seemed to be at least partly effective. Increasing either the concentration or the viscosity type of Methocel waa not effective.
Dialysis fermentation. III. Anomalous inhibition of threonine biosynthesis in an auxotrophic mutant of Escherichia coli
Authors: Abbott Bernard J. , Gerhardt Philipp
Published: December 2004

Dialysis was attempted as a means to alleviate the product‐activated controls presumed to limit the formation of threonine by an auxotrophic mutant of Escherichia coli strain W. The occurrence of inhibition rather than enhancement of yields by dialysis was traced to the fact that threonine actually was not inhibiting its own synthesis. Instead, α,ε‐diaminopimelic acid became depleted, but the imbalance could not be corrected by exogenous replacement.
Inactivation of immobilized catalase by hydrogen peroxide in continuous reactors
Authors: O'Neill S. P.
Published: December 2004

It is shown theoretically that in continuous reactions the rate of catalase inactivation by hydrogen peroxide depends on the type of reactor and the order of the chemical reaction.
Measurements on the interfacial areas of hydrocarbon in yeast fermentations and relationships to specific growth rates
Authors: Wang Daniel I. C. , Ochoa Alberto
Published: December 2004

The transport of insoluble substrates such as hydrocarbons to microorganisms is often postulated to be dictated by the availability of the hydrocarbon surface area. Many publications, qualitative and quantitative, have appeared to substantiate this hypothesis. Experiments have been performed in our laboratory to assess the absolute values of the interfacial area of hexadecane as the carbon source for the growth of Candida intermedia. A sedimentometer, mounted directly in the fermentor, was used to measure the interfacial hydrocarbon area during active growth of this organism. The specific hydrocarbon interfacial area was found to be directly related to the impeller speed, hydrocarbon concentration and surfactant concentration in a 1‐liter working volume, turbine‐agitated fermentor. The specific growth rate was in turn found to be directly related to the specific hydrocarbon interfacial area. Lastly, cessation of logarithmic growth and onset of linear growth was found at all instances to be governed by the specific hydrocarbon surface area.
Reduction of the nucleic acid content of single‐cell protein concentrates
Authors: Hedenskog Gudmund , Ebbinghaus Lars
Published: December 2004

Methods for reducing the content of nucleic acid in protein concentrates from disintegrated yeast and microalgae were investigated. Protein concentrates were prepared by acid precipitation of extracted protein after cell wall separation. The influence of alkaline protein extraction on the content of RNA in isoelectrically precipitated protein concentrates was studied. It was found that when a strong decrease in the RNA content was obtained, this was followed by a decrease in the yield of protein concentrate. Protein concentrates were also prepared without cell wall separation by precipitation with different agents after cell disintegration. In the precipitates from microalgae, a RNA reduction was obtained. Precipitation of yeast, protein gave no essential reduction with the precipitants used. Precipitation of yeast protein by heating at an alkaline pH gave a protein concentrate with a low content of RNA. A slightly lower RNA content was obtained when the precipitation was performed in the presence of NaCl. The yield of amino acid nitrogen was 70–80% and the RNA content was 1–2%. A process with precipitation at alkaline pH for the production of microbial protein concentrates with a low content of nucleic acid is suggested.
The fermentation of L‐sorbose by Gluconobacter melanogenus. I. General characteristics of the fermentation
Authors: Tsukada Y. , Perlman D.
Published: December 2004

Growing cultures, washed cells, and cell‐free preparations of Gluconobacter melanogecnus IFO 3293 converted L‐sorbose to 2‐keto‐L‐gulonic acid, to D‐sorbitol (which was metabolized further) and to 5‐keto‐D‐fructose.
Estimation of parameters in population models for Schizosaccharomyces pombe from chemostat data
Authors: Kothari Indravadan R. , Martin Gregory C. , Reilly Peter J. , Martin Peter J. , Eakman James M.
Published: December 2004

The integro‐differential growth model of Eakman, Fredriekson, and Tsuehiya has been employed to fit cell size distribution data for Schizosaccharomyces pombe grown in a chemostat under severe product inhibition by ethanol. The distributions were obtained with a Coulter aperture and an electronic system patterned after that of Harvey and Marr. Four parameters—mean cell division size, cell division size standard deviation, daughter cell size standard deviation, and a growth rate coefficient—were calculated for models where the cell growth rate was inversely proportional to size, constant, and proportional to size. A fourth model, one where sigmoidal growth behavior was simulated by two linear growth segments, was also investigated. Linear and sigmoidal models fit the distribution data best. While the mean cell division size remained relatively constant at all growth rates, standard deviation of division size distribution increased with increasing holding times. Standard deviation of the daughter size distribution remained small at all dilution rates. Unlike previous findings with other organisms, the average cell size of Schizosaccharomyces pobme increased at low growth rates.
The kinetic and mass transfer behavior of immobilized invertase on ion‐exchange resin beads
Authors: Kobayashi Takeshi , Moo‐Young M.
Published: December 2004

Immobilized invertase was prepared by binding native invertase to a polyamine type ion‐exchange resin. Kinetic behavior of the immobilized invertase on these small pellets was investigated in a packed‐bed reactor. For low flow rates, an effect of interparticle diffusion on the Machaelis constant was observed and a correlation was proposed to evaluate the effect. At high flow rates, Michaelis and inhibition constants were determined and compared with those for native invertase. With large pellets, intraparticle diffusion was found to be important and at high substrate concentrations, the effectiveness factor exceeded unity. Good agreement was found between the theoretical analyses and the experimental data.
The influence of environmental conditions on the macromolecular composition of Candida utilis
Authors: Alroy Y. , Tannenbaum S. R.
Published: December 2004

Glucose‐limited chemostat cultures of Candida utilis were cultivated at various pH levels (3.0–7.5), temperatures (15–37.5°C), dilution rates (0.06–0.42 hr−1), and with different nitrogen sources (NH and NO). The ratio of total nucleic acid to protein increased with increase in dilution rate at constant temperature and decreased with increase in temperature at constant dilution rate. The pattern of these variations is consistent with the hypothesis that the nucleic acid to protein ratio is a function of the ratio of the actual dilution rate to the critical dilution rate corresponding to each one of the cultivation temperatures. This ratio is called “reduced dilution rate.” A basis is proposed on which various microorganisms may be compared with respect to the ratios of cell protein to nucleic acid, RNA, ribosomal RNA, and polysomes.
Large scale isolation of choline acetyltransferase from ox brains
Authors: Street G. , Dunnill P. , Lilly M. D. , Glover Vivette A. S.
Published: December 2004

A process for the large‐scale isolation of choline acetyltransferase from ox brain has been developed, by scaling‐up an existing laboratory method. 20% of the enzyme was obtained from 17 kg of brain tissue with a 50‐fold purification.
New methods for binding enzyme molecules into a water‐insoluble matrix: Properties after insolubilization
Authors: Broun G. , Thomas D. , Gellf G. , Domurado D. , Berjonneau A. M. , Guillon C.
Published: December 2004

New methods of crosslinking enzyme molecules inside a matrix with or without an inactive protein are described. Enzyme activity yields range between 30 and 80% of the activity of the untreated preparations. Even fragile enzyme systems, for instance those using mobile cofactors, can be efficiently immobilized. Increased resistance towards heat denaturation and proteolysis results.
Dynamic analysis of a microbial process: A systems engineering approach
Authors: Young Thomas B. , Bungay Henry R.
Published: December 2004

A general mathematical model of the chemostat system is developed in order to define an experimental program of dynamic testing. A glucose‐limited culture ofSaccharomyces cerevisiae was grown in a chemostat using chemically defined medium. The chemostat was perturbed from an initial steady state by changes in input glucose concentration, dilution rate, pH, and temperature. Dynamic responses of cell mass, glucose, cell number, RNA, and protein concentrations were measured. A number of simulation techniques were used in developing a dynamic mathematical model and in comparing the developed model with experimental data as well as the Monod model. The resulting model was found to be quantitatively accurate and superior to the Monod model. The developed model was interpreted in the light of cell physiology. Adjustment of intracellular RNA fraction was found to be rate limiting in acceleration of cell specific growth rate.
The “azotopure” process for treating nitrogen‐deficient aqueous wastes
Authors: Finn Robert K. , Tannahill Alex L.
Published: December 2004

Many chemical and food processing wastes are deficient in nitrogen, and must therefore be supplemented with domestic sewage or ammonia to dispose of them by conventional biological treatment. A more economical treatment, especially of strong wastes, is possible by maintaining a semipure culture of nitrogen‐fixing bacteria in a stirred aerated tank. When operated as a chemostat with 4 to 6 hr detention time, removal of 85% of the COD is possible in a single step without the need for clarifiers or digesters. A clarified effluent could also be produced by flotation or sedimentation of the flocculated bacteria. In that case there would be 99% removal of COD and a reduction in the amount of sludge by two‐thirds over the conventional activated sludge process.
ATP regeneration using immobilized carbamyl phosphokinase
Authors: Marshall David L.
Published: December 2004

A simple and efficient system for continuous ATP regeneration is described. The procedure is based on the enzyme‐catalyzed reaction between carbamyl phosphate and ADP. The carbamyl phosphate was generated in situ by reaction between potassium cyanate and potassium phosphate. The enzyme, carbamyl phosphokinase, was isolated from extracts of Streptococcus faccalis and partially purified. Immobilization of the enzyme was achieved using glutaraldehyde‐treated alkylamine glass giving 200–250 units of activity per gram of glass. A column of carbamyl phosphokinase on glass was used to form ATP continuously from ADP, phosphate, and cyanate and lost approximately 16% of the initial activity after 14 days operation at room temperature.
Studies on immobilized papain
Authors: Weetall H. H. , Mason R. D.
Published: December 2004

Papain was covalently coupled to ZrO2−coated porous glass by several different methods. These derivatives were characterized and their operational half‐lives determined using casein substrate. Papain covalently coupled to the porous glass, previously converted to a carboxylic acid derivative, through amide linkage gave a 35 day operational half‐life.
Preparation and properties of an immobilized Barley β‐amylase
Authors: Vretblad Per , Axen Rolf
Published: December 2004

Barely β‐amylase (α‐1,4‐glucan maltohydrolase, EC 3.2.1.2) has been immobilized by covalent fixation to amino derivatives of epichlorohydrin crosslinked Sepharose mediated by cyclohexyl isocyanide and acetaldehyde. The enzyme conjugates contain up to 35% of the total activity of the β‐amylase added to the coupling mixture. The profiles of activity versus pH and ionic strength are essentially the same for free and immobilized β‐amylase, whereas the resistance to inactivation during storage and use is considerably enhanced by immobilization. Columns with immobilized β‐amylase have been used for continuous degradation of starch. At 45°C, half of the initial activity remains after seven weeks, and the corresponding figure at 23°C is 85 percent.
Mixed culture biooxidation of phenol. II. Steady state experiments in continuous culture
Authors: Pawlowsky U. , Howell J. A.
Published: December 2004

Experiments are reported in which a mixed population of organisms was continuous cultured on phenol in a 1‐ to 2‐liter well‐mixed vessel. Steady state phenol concentrations were measured for a range of inlet concentrations from 100 to 800 mg/liter at various dilution rates. These results were compared with those predicted from a model which incorporates the effect of wall growth. It was found that the effect of growth on the walls of the vessel was considerable and increased by a factor of up to 3 × the dilution rate at which 90% conversion of phenol could be obtained.
Insolubilized amylases
Authors: Walton Henry M. , Eastman James E.
Published: December 2004

Carrier‐bound immobilized α‐amylases and glucoamylase have been obtained by photopolymerizing aqueous solutions containing acrylamide, a crosslinking monomer, an enzyme‐reactive monomer, an oxygen scavenger, and amylase, and allowing the amylase to react with the entrapping enzyme‐reactive gel matrix evolved. Partial starch hydrolyzates (28 DE corn starch syrup) have been continuously converted to 90–94% dextrose syrups in columns packed with immobilized amylases. The enzymatic heat stability of immobilized glucoamylase gels is discussed.
Citrate production from hydrocarbons by use of a nonsterile, semicontinuous cell recycle system
Authors: Gledhill W. E. , Hill I. D. , Hodson P. H.
Published: December 2004

In order to minimize product toxicity, decrease fermentation cost, prolong the effective production phase, and shorten the lag phase before production in the citrate‐hydrocarbon fermentation by Candida lipolytica ATCC 8661, the use of a nonsterile semicontinuous cell recycle system was investigated. Model experiments demonstrated that portions of the fermentor broth could periodically be removed and centrifuged under nonaseptic conditions with the cells being added to fresh medium and returned to the fermentor. Citrate production continued, however with repeated semicontinuous cell recycle, acid production gradually decreased. It was postulated that this decrease could be attributed largely to physiological trauma and that a truly continuous cell recycle system would minimize these effects and permit maintenance of higher citrate production rates.
Estimation of the disruption in freeze‐pressed Accharomyces cerevisiae by an electronic particle counter
Authors: Magnusson Karl‐Eric , Edebo Lars
Published: December 2004

An electronic particle counter has been used to estimate the disintegration by freeze‐pressing baker's yeast. A counter threshold level which just yielded the maximum count for intact cells was selected. The conductivity of the suspending medium was chosen such that maximum counts were obtained. Under these conditions, the electronic counts agreed well with the visual counts. At a certain threshold level the maximum count was obtained at a lower resistivity (higher conductivity) in the suspending solution with the freeze‐pressed suspension than with untreated cells, indicating that damage to the permeability barrier may occur without disruntion of the cell envelope.

Fresh baker's yeast cells do not behave as nonconducting particles. This has to be taken into account when volume determinations with electronic particle counters are performed.
Continuous Cellulase Production
Authors: Mitra Gautam , Wilke Charles R.
Published: December 2004

Trichoderma viride QM 9414 growth characteristics on glucose were investigated in single stage continuous stirred tank reactor operation and growth parameters μmax, Ks, QO2 identified. Multistage stirred tank fermentors in series with the first stage utilizing glucose and the subsequent stages utilizing cellulose yielded results in general agreement with theoretical predictions. Significant increase in enzyme productivity over single stage fermentation was obtained in multistage operation.
The design of stirred reactors with hollow fiber catalysts for Michaelis‐Menten kinetics
Authors: Georgakis C. , Chan P. C‐H. , Aris R.
Published: December 2004

A method of calculating the conversion in Rony's hollow fiber reactor is outlined. It, is assumed that, the kinetics are of Michaelis‐Menten type and that diffusion within the hollow fiber, as well as through its wall, should be taken into account. The normalization of the Thiele modulus suffices to unify the treatment of internal diffusion and the pseudosteady state hypothesis is found to be valid under almost all conditions.
An evaluation of suspension culture systems for the growth of murine lymphoblastoid lines expressing TL and Thy‐1 alloantigens
Authors: Zwerner Robert K. , Runyan Charles , Cox R. Michael , Lynn Daniel , Acton Ronald T.
Published: December 2004

As a prelude to our studies on TL and Thy‐1 differentiation alloantigens, three murine lymphobhastoid cell lines were examined for expression of these components. Optimal conditions for their mass culture were also determined. Several suspension culture systems were evaluated: (a) 50 ml through 500 ml Wheaton and Bellco spinner flasks as well as 1, 4, and 8 liter Wheaton flasks modified for semicontinuous culture conditions, (b) 3 liter Chemapec Vibrofermentor, and (c) 14 liter New Brunswick fermentor. Utilizing these types of vessels the optimal culture conditions were evaluated as to the effect of: (1) pH, (2) initial concentration of cell inoculum, (3) types of media, and (4) methods of gassing and gas mixtures on the rate of growth and alloantigen expression. This study demonstrated that cells could be cultured on a semicontinuous basis up to densities of 2–4 × 106 cells/ml if a vessel of appropriate dimensions was utilized, the appropriate medium selected, and the pH controlled by CO2 and air overlay. Once these parameters were established the growth of a given cell line was highly reproducible: Under optimal culture conditions the expression of Thy‐1 was maximum while the cells were in the exponential stage of growth and reduced during the lag and stationary phases of growth. The expression of TL did not vary as significantly during the various stages of growth. One cell line grown in medium supplemented with 10% horse serum expressed lass Thy‐1 than those grown in medium containing 10% fetal calf serum. The factors affecting cell growth and alloantigen expression have been considered in the design of a large‐scale suspension culture facility for culturing 1000 liters of cells per week.
Maintenance of perpetual synchrony in HeLa suspension cultures: Question of unbalanced growth
Authors: Thilly W. G. , Arkin D. I. , Nowak T. S. , Wogan G. N.
Published: December 2004

Unbalanced growth has been studied in HeLa cell cultures maintained in perpetual division synchrony by periodic inhibition of DNA synthesis. Observation of eight independent cellular parameters indicates that once synchrony has been established the degree of unbalanced growth in later cycles is not as great as is observed with the conventional “double‐block” technique. This significant diminution of unbalanced growth appears to be related to the significantly shorter periods of inhibition of DNA synthesis used in the resynchronization process.
Autoclavable low cost serum‐free cell culture media. The growth of L Cells and BHK cells on peptones
Authors: Keay Leonard
Published: December 2004

The growth of L‐929 cells on a series of peptones, and protein hydrolysates was examined, and it was found that when MEM was supplemented with any of a series of peptones, cell growth was about as good as when serum was used as a supplement. Protein hydrolysates did not support cell growth very well and at higher concentrations actually reduced cell growth. L‐929 and L‐60TM cells were grown both as monolayers or stationary suspensions and in agitated systems in MEM supplemented with 0.5—1% bactopeptone. The addition of macromolecular compounds, insulin or oleic acid had no effect on cell growth. BHK cells were also grown on media supplemented with bactopeptone but richer media (MEM‐alpha, F‐12, or RMPI1640) gave higher cell yields. The cells did not form the monolayers observed with fetal calf serum, but a partial suspension system. Addition of a detergent Darvan #2 gave a totally suspension culture in both stationary and agitated systems.

The production of Sindbis virus in BHK cells grown in serum‐free media was examined and the yield of virus was found to be about the same as that produced in serum‐supplemented systems. It is estimated that the cost of cell production media could be reduced by about 90% by the replacement of serum supplement by peptones.
Microbial systems for study of the biotransformations of drugs
Authors: Smith Robert V. , Rosazza John P.
Published: December 2004

The metabolic fate of drugs and other xenobiotics in mammalian organisms represents an area of intense contemporary interest. Traditionally, it is a difficult area of research becausethe biological systems which are used to study biotransformations are capable of yielding only minute quantities of metabolites. Recent developments in comparative biochemistry have made itpossible to link diverse metabolic systems through similarities in the pathways by which they alter foreign organic compounds. The potential thus exists for utilizing microbial metabolic systems to study and possibly predict the metabolic fate of a drug or other foreign compound in mammals. The ease with which microbial systems may be used to obtain large amounts of metabolites is an obvious Advantage.

We havhe attemped to review the ways in which mammalian and microbialorganisms metabolize a variety of organic compounds. Attention has been focused on the similarities and differences in the mechanisms by which these living systems metabolize xenobiotics. Particular emphasis has been given to four types of reactions which are important in drug biotransformations: aromatic hydroxylationl; N‐ and O‐dealkylations; and sulfur oxygenations.
A hydrodynamic mechanism for the disintegration of Saccharomyces cerevisiae in an industrial homogenizer
Authors: Doulah M. S. , Hammond T. H. , Brookman J. S. G.
Published: December 2004

Amongst the commercial type of homogenizers the Manton‐GaulinAPV homogenizer (APV Company Ltd., Crawley, Surrey, England) which is generally being used for other purposes than cell disintegration processes, has recently been proved to be effective for the breakage of yeast cells. To understand fully the disintegration process occurring in such machines it becomes necessary to describe their functions through mathematical expressionsbased on a realistic hydrodynamic model.

A mathematical expression describing the protein release at an applied pressure has been derived from an energy balance in the homogenizer combined with the size distribution function of yeast cell population. This expression has been confirmed experimentally under conditions where it shows that turbulence is the controlling factor in the system. Furthermore it indicates the area where more investigations are needed to improve the efficiency of the process of disintegration.
Kinetics of solka floc cellulose hydrolysis by trichoderma viride cellulase
Authors: Howell J. A. , Stuck J. D.
Published: December 2004

A product inhibition model is developed to describe the hydrolysis of cellulose by the Trichoderma viride enzyme system. It is assumed that noncompetitive inhibition by cellobiose dominates the reaction kinetics. Experiments show that this is indeed a reasonable assumption for initial cellulose concentrations of up to 15 g/liter and at hydrolysis extents up to 65′. Kinetic parameters were determined for the noncompetitive inhibitionmodel in batch experiments with durations of up to 1.5 hr. These parameterswere then used in predicting reaction progress for up to 10 hr. Cellobiose was added to the reaction mixture at the onset of some runs and againreliable predictions were obtained for up to 8 hr of hydrolysis. Finally reaction was carried out in a membrane reactor whereby the product cellobiose was being continuously removed and again reasonable predictability was obtained with a higher net reaction rate.
Electrostatic and hydrophobic effects in affinity chromatography
Authors: Morrow R. M. , Carbonell R. G. , McCoy B. J.
Published: December 2004

A semi–quantitative theory is developed to explain the nonspecific binding of proteins to substituted affinity chromatography supports due to electrostatic and hydrophobic interactions. The equilibrium constant for the absorption of an enzyme to a solid support, and the rate of desorption of the enzyme are studied as functions of ionic strength. Experimental measurements were taken of the adsorption equilibrium constant and rate of desorption of E. coli β–galactosidase on Sepharose 4B substituted with 3, 3,‐diaminodipropylamine in batch systems. It was found that the enzyme adsorption exhibits a hysteresis effect as the ionic strength is increased and then decreased. Furthermore, the adsorption of theenzyme becomes more reversible at the lower ionic strengths, while at the higher ionic strengths it is essentially irreversible. Using the measured equilibrium constants, and knowing the region of ionic strength where the adsorption becomes reversible, we were able to predict the desorption of enzyme in a continuous stirred tank as a function of time when a decreasing linear gradient of ionic strength was introduced into a slurry. It was found that the presence of another protein, hemoglobin, does not affect these results, and therefore can be separated from the enzyme.
Kinetics of biosynthesis of polyene macrolide antibiotics in batch cultures: Cell maturation time
Authors: Martin Juan F. , McDaniel Lloyd E.
Published: December 2004

The changes in several parameters of the candicidin fermentation (total, mycelium‐associated, and extracellular product formation; growth rate; DNA content; glucose utilization; dissolved oxygen in the broth; and oxygen uptake rate) during the trophophase‐idiophase transition are compared with previously reported data for the polyene macrolides, candidin and candihexin. The maturation time, tm, and the productformation rate constant, kp, have been calculated for each of the three polyene macrolides using a simple mathematical model. Slow‐feeding of glucose, which resulted in candidin and candihexin overproduction has been shown to increase the polyene formation rate constant and toretard trophophase to idiophase transition (longer maturation time). The opposite effect is achieved by repeated feeding of soybean meal. The values of the maturation times and polyene formation rates obtained were used to predict the production of polyene macrolide antibiotics in batch cultures.