bluuebunny/crossref_metadata_2025_split 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

AbstractThe 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

AbstractIn 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractMathematical 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.
A modified adsorption method for determining percentage of dead yeast cells
Authors: Vairo Marina L. R. 
Published: December 2004

AbstractThe 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

AbstractThe 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.
Stripping in sparged fermentation systems. I. Two component model systems
Authors: Hamer G. 
Published: December 2004

AbstractA 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

AbstractThe 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

AbstractContinuous 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

AbstractLarge 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

AbstractPseudomonas 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

AbstractAn 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

AbstractThe 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

AbstractEarlier 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

AbstractIn 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

AbstractDialysis 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.
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

AbstractThe 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

AbstractMethods 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

AbstractGrowing 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.