bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermally induced protein gelation: Gelation and rheological characterization of highly concentrated ovalbumin and soybean protein gels
Authors: Van Kleef F. S. M. 
Published: May 2005

AbstractIn order to optimize the use of proteins as functional ingredients in foods, one needs more insight into the effects of environmental conditions (pH, ionic strength, and temperature) on the functional properties of protein. This paper summarizes the results of an extensive study on heat‐induced gelation of ovalbumin (egg‐white protein) and soybean protein in the concentration range from 10 to 35 g/100 g. It was the aim of the study to relate the rheological properties of thermally induced protein gels to the microstructure of the gel and the physicochemical properties of the constituent protein. The gelling behavior of the protein was quantified with rheological techniques, and the physical properties of the gels were determined, at small and large deformations. From the swelling/dissolving behavior of the gels in various media, the nature of the crosslinks was determined qualitatively. The microstructure of the gels was determined with electron microscopy. Nmr‐spectroscopy was applied in order to elucidate changes in conformation during heating. It was found that the formation of a continuous covalently crosslinked network is not a prerequisite for thermally‐induced protein gelation. The properties of a gel strongly depend on the pH at which the gel is formed. When heat‐set at high pH(pH∼10), a homogeneous, strong, and almost transparent gel is formed, consisting of flexible crosslinked protein gels. Heat‐setting at low pH (pH 5) leads to the formation of a heterogeneous and weak gel, which easily exudes water. This gel consists of crosslinked aggregated protein. The ionic strength of the solvent in which the protein is dissolved and heat‐set has a much lower effect on gel properties.
Unusual conformational transitions of leucine‐containing basic polytripeptides
Authors: Šokrová ŠTěPánka , Bohdanecký Miloslav , Ček Blahoslav Sedlá , Bláha Karel , Šponar Jaroslav 
Published: May 2005

AbstractThe conformational transitions of synthetic basic polytripeptides (Lys‐Leu‐Gly)n, (A2bu‐Leu‐Gly)n, (Lys‐Leu‐Ala)n, and (A2bu‐Leu‐Ala)n induced by high salt concentrations and elevated pH were investigated by CD, ir, and 1H‐nmr spectroscopy, sedimentation analysis, viscometry, and light scattering. Sheet aggregates of chains in a conformation similar to the polyglycine II (polyproline II) helix, bound together by hydrogen bonds, are the most probable form of (Lys‐Leu‐Gly)n and also, partly, of (A2bu‐Leu‐Gly)n in a high‐pH or high‐salt solutions. The conformation (Lys‐Leu‐Ala)n, in a low‐salt concentration, is an α‐helix. Since (A2bu‐Leu‐Ala)n is disordered under similar conditions, it appears that this α‐helix is stabilized by hydrophobic interactions between Lys and Leu side chains. In a high concentration of water structure‐making ions, CD data for (Lys‐Leu‐Ala)n indicate distortion of the α‐helix, with a parallel increase in the average molecular weight corresponding to trimer formation. Hydrodynamic data are consistent with a model of bundles of three closely touching spherocylinders. (A2bu‐Leu‐Ala)n shows a limited tendency to α‐helix formation.
Circular dichroism of double‐stranded RNA in the presence of salt and ethanol
Authors: Steely H. Thomas , Gray Donald M. , Lang Dimitrij , Maestre Marcos F. 
Published: May 2005

AbstractWe have investigated CD spectra of double‐stranded RNA (dsRNA) in a variety of ethanolic and salt solutions. Solution conditions were varied by the addition of salts and ethanol, alone, or in combinations. (1) On addition of either salt or ethanol alone to solutions of dsRNA, we found that the positive CD band at 264 nm increased by up to 7% (in salt) or 12% (in ethanol) and underwent a long‐wavelength shift of 3 nm. Concomitantly, the negative CD band at 296 nm decreased. These CD changes may be indicative of an A‐ to A′‐RNA secondary‐conformation change on dehydration. (2) On addition of both salt and ethanol, in various combinations that caused precipitation of dsRNA, three types of CD spectral changes were found, which we take to indicate at least two different types of intermolecular arrays of RNA molecules. Type I precipitate was flocculent and its CD spectrum had a differential scattering component at long wavelengths. Type II condensate was finely dispersed and was characterized by a doubling of the CD magnitude at 264 nm and simultaneous disappearance of the 210 nm band, to give a CD spectrum close to that previously reported for RNA condensed in the presence of polyethylene glycol and salt [Ψ+ RNA; Evdokimov, Y.M., Pyatigorskaya, T.L., Kadikov, V.A., Polyvtsev, O.F., Doskocil, J., Koudelka, J. & Varshavsky, Y.M., (1976) Nucleic Acids Res. 3, 1533–1547]. Type III precipitate was flocculent and had CD spectra that included features that were present for Types I and II condensates; thus, the RNA in this precipitate may not have been in a unique intermolecular array.
Study of the circular dichroism of bacteriophage ϕ6 and ϕ6 nucleocapsid
Authors: Steely H. Thomas , Gray Donald M. , Lang Dimitrij 
Published: May 2005

AbstractWe have studied the CD of both bacteriophage ϕ6 and ϕ6 nucleocapsid in order to assess the in situ state of the viral, double‐stranded RNA (dsRNA). The results showed that packaged ϕ6 RNA is slightly hyperdichroic (4–5%) at 264 nm relative to dsRNA in solution. Also, the CD of dsRNA within both the virus and the nucleocapsid was unlike CD spectra of any of the three types of dsRNA condensed in vitro, as described in the accompanying paper. Using a curve‐fitting program described elsewhere (Edmondson, S.P. & Gray, D.M. (1983) Nucleic Acids Res. 11, 175–192), we have fit reference CD spectra of ϕ6 RNA and protein to measured CD spectra of ϕ6 intact phage and nucleocapsid. Results of the computer analysis indicated that ϕ6 RNA in situ is spectrally similar to dsRNA that is slightly dehydrated.
23Na‐nmr investigations of counterion exchange reactions of helical DNA
Authors: Braunlin W. H. , Anderson C. F. , Record M. Thomas 
Published: May 2005

AbstractChanges in Δν½, the nmr linewidth of 23Na, have been determined during titrations of helical DNA with polyamines (divalent putrescine and trivalent spermidine) and with inorganic cations (Mg2+ and Co(NH3)). In each case additions of a multivalent cation (Mz+) to a solution containing NaDNA and NaCl cause decreases in Δν½, which is a population‐weighted average of contributions from nuclei in bound and free environments. Thus, the binding of Mz+ to DNA displaces sodium ions from regions where the quadrupolar relaxation of 23Na is relatively efficient. At a given extent of titration, the binding of a polyamine produces a smaller decrease in Δν½ than does the binding of an inorganic ion of the same valence. The concentration dependence of Δν½ during the course of a titration can be interpreted most simply as a two‐state ion‐exchange reaction by assuming that the binding of Mz does not alter RB, the average relaxation rate of sodium nuclei that remain bound. On the basis of this assumption, the initial linear portions of titration curves can be analyzed to determine upper bounds for r°, the number of sodium ions bound per DNA phosphate in the absence of any competing counterion. Analyzing the titration curves for the four multivalent competitors leads to a range of upper‐bound estimates for r°: 0.5–0.8. The differences in these estimates could indicate that polyamines displace fewer sodium ions from DNA than do their smaller inorganic counterparts. Alternatively, the range in upper‐bound estimates for r° could also reflect specific differences in the effects of the various multivalent cations on RB, if this relaxation rate does change during titration.
1H‐nmr studies of a monointercalating drug into a d[CpGpCpG]2 minihelix
Authors: Delepierre Muriel , Delbarre A. , D'Estaintot B. Langlois , Igolen J. , Roques B. P. 
Published: May 2005

AbstractThe structure of the complex formed between the 7H‐pyridocarbazole monomer [{(2‐piperidyl)‐2,1‐ethane‐yl} {10‐methoxy‐7H‐pyrido[4,3‐c]carbazolium} dimethane sulfonate] and the autocom‐plementary tetranucleotide d(CpGpCpG)2 in aqueous solution is analyzed by 270‐MHz and 400‐MHz 1H‐nmr. The strong upfield shifts observed on most aromatic resonances of both the drug and the nucleotide are interpreted as the result of intercalation of the 7H‐pyridocarbazole monomer in the base‐paired minihelix of d(CpGpCpG). The observation of intermolecular negative nuclear Overhauser effects induced in some drug resonances by irradiation of sugar protons confirms this conclusion. A privileged orientation of the drug in the intercalation site with the quaternizing ethyl piperidine chain protruding in the major groove is proposed.
Interaction of amphipathic polypeptides with phospholipids: Characterization of conformations and the CD of oriented β‐sheets
Authors: Bazzi Mohammed D. , Woody Robert W. , Brack André 
Published: May 2005

AbstractThe effects of interaction with phospholipids on the conformation of the alternating copolymer, poly(Leu‐Lys), and the random copolymer poly(Leu50, Lys50) have been investigated by CD and ir spectroscopy. Poly(Leu‐Lys) undergoes a partial unordered → β‐sheet transition in solution in the presence of lysolecithin. On addition of lysolecithin plus cholate, an unordered → α ‐helix transition is observed. In films deposited from these solutions, poly(Leu‐Lys) adopts the anti‐parallel β‐sheet conformation, as in aqueous solutions at moderate ionic strength. Polarized ir spectra showed that the plane of the β‐sheet in such films deviates from the plane of the film by no more than 14°. The random copolymer, poly(Leu50, Lys50), is α‐helical in the presence of lysolecithin and lysolecithin plus cholate, regardless of whether the sample is a solution or a film. CD measurements on the poly(Leu‐Lys) films provide information about the component of the CD tensor for light propagating normal to the plane of the β‐sheet. These measurements show (1) a negative n → π* CD band (214 nm maximum) with higher intensity than the average CD for isotropic solution; and (2) a positive band in the π → π* region (195 nm maximum), which is weaker than that in the isotropic spectrum.
The effect of methylmercury(II) binding on the conformation of poly(L‐glutamic acid) and poly(L‐lysine): A raman spectroscopic study
Authors: Alex S. , Tajmir‐Riahi H. A. , Savoie R. 
Published: May 2005

AbstractThe binding of the methylmercury cation CH3Hg+ by poly(L‐glutamic acid) (PGA) and by poly(L‐lysine) (PLL) has been investigated by Raman spectroscopy. Coordination on the side‐chain COO− and NH groups of these polypeptides gave characteristic ligand–Hg stretching modes at ca. 505 and 450 cm−1, respectively. Precipitation generally occurred upon formation of the complexes and changes of conformation were common. The solid complex obtained from PGA at pH 4.6 was found to have a mostly disordered conformation, which differed from the respective α‐helical and β‐sheet structures of the dissolved and precipitated uncomplexed polypeptide in the same conditions. An α‐helical structure was generally adopted by the complex formed with PLL, even in pH and temperature conditions where the free polypeptide normally exists in another conformation. The addition of a stronger complexing agent, glutathione, to the PLL/CH3Hg+ complex caused a migration of the bound cations and a restoration of the polypeptide to its original state.
Polynucleotide base‐pair orientation in solution: Linear dichroism and molecular mechanical studies of poly[d(A)]‐poly[d(T)]
Authors: Edmondson Stephen P. 
Published: May 2005

AbstractModel helices for poly[d(A)]‐poly[d(T)] in solution were constructed based on the base orientations determined by linear dichroism [LD; S. P. Edmondson & W. C. Johnson, Jr. (1985) Biopolymers 24, 824–841] and refined by molecular mechanical energy minimization. The results demonstrate that poly[d(A)]‐poly[d(T)] can form energetically stable conformations with the base orientations measured by LD. Further, only one of the four possible base‐pair orientations that are consistent with the LD results is feasible. Models with negative base tilts had large potential energies, indicating that the LD results do not reflect base motions. The LD models of poly[d(A)]‐poly[d(T)] are stabilized mainly by intrastrand base‐stacking interactions, particularly for the adenine strand.
Conformational heterogeneity of quinoxaline peptides in solution
Authors: Alfredson Thomas V. , Maki August H. , Waring Michael J. 
Published: May 2005

AbstractThe conformational heterogeneity of several quinoxaline antibiotics, a class of naturally occurring quinoxaline peptides with antitumor properties, and their synthetic analogues was investigated in polar and nonpolar solvents by high performance liquid chromatography (HPLC) with uv photodiode array detection, uv‐absorbance, low‐temperature phosphorescence, and nmr techniques. Multiple peak formation and interconversion in the HPLC and 1H‐nmr analysis of triostin A, its under‐N‐methylated synthetic analogues (des‐N‐tetramethyltriostin A [TANDEM] and [N‐MeCys3, N‐MeCys7]‐TANDEM [MCTANDEM]), and echinomycin were examined as a function of temperature, solvent polarity, and residence time in solution prior to analysis. Slow interconversion between HPLC peaks, ascribed to the presence of multiple solution conformers, was exhibited by these peptides although at very different interconversion rates. Among the triostins, the rate of interconversion appeared to vary with the degree of N‐methylation of the residues in the cyclic depsipeptide chain. Interconversion of the n and p conformers of triostin A in chloroform occurred on a chromatographic timescale (a few minutes with kn→p calculated to be 0.02 s−1 at 25°C) while the solution conformers of TANDEM in methanol equilibrated very slowly to one preferred conformer over a period of several weeks at ambient temperature. MCTANDEM, a synthetic analogue of triostin A with an intermediate degree of N‐methylation of the residues in the peptide ring, consisted of an equilibrium mixture of n and p conformers in methanol that interconverted on a chromatographic time scale. Two additional conformers of MCTANDEM developed within a few weeks' residence time in methanol at ambient temperature. Echinomycin was found to exist in methanol as an interconverting mixture of at least four minor conformers in addition to the major isoform (95% by peak area) of the peptide. The solution conformers of the quinoxaline peptides investigated in this report are most likely a consequence of hindered rotation about the N‐methylated peptide bonds in the depsipeptide ring and/or intramolecular hydrogen bonding.
Modified chemotactic peptides: synthesis, crystal conformation, and activity of For‐Hse(Me)‐Leu‐Phe‐OMe
Authors: Torrini I. , Zecchini G. Pagani , Paradisi M. Paglialunga , Lucente G. , Gavuzzo E. , Mazza F. , Pochetti G. , Traniello S. , Spisani S. 
Published: May 2005

AbstractThe presence of the sulfur atom of the methionine side chain exerts significant effects at different levels on biochemical behavior of chemotactic N‐formylpeptides. In order to acquire more information on this point, the synthesis, the conformation in the crystal, and the activity of For‐Hse(Me)‐Leu‐Phe‐OMe (2)—an oxygen analogue of For‐Met‐Leu‐Phe‐OMe (f MLP‐OMe) containing the O‐methyl‐L‐homoserine in place of the native methionine at position 1—is reported. The new analogue 2 adopts a conformation that is extended at the first two residues and folded at the C‐terminal phenylalanine. This conformation is different from that of the parent f MLP‐OMe and strikingly similar to that adopted by f MLP‐OBut. The side‐chain spatial orientation of 2 corresponds to that adopted by f MLP‐OH when cocrystallized with an immunoglobulin possessing binding properties similar to those of neutrophil receptors. When tested on human neutrophils the formylpeptide 2 is more active than the parent in the stimulation of directed mobility and maintains both the granule enzyme release activity an the superoxide anion production. © 1994 John Wiley & Sons, Inc.
Hydrodynamics and mass transfer coefficient in activated sludge aerated stirred column reactor: experimental analysis and modeling
Authors: Jin Bo , Lant Paul , Ge Xiangyu 
Published: May 2005

AbstractThe aerated stirred reactor (ASR) has been widely used in biochemical and wastewater treatment processes. The information describing how the activated sludge properties and operation conditions affect the hydrodynamics and mass transfer coefficient is missing in the literature. The aim of this study was to investigate the influence of flow regime, superficial gas velocity (UG), power consumption unit (P/VL), sludge loading, and apparent viscosity (μap) of activated sludge fluid on the mixing time (tm), gas hold‐up (ε), and volumetric mass transfer coefficient (kLa) in an activated sludge aerated stirred column reactor (ASCR). The activated sludge fluid performed a non‐Newtonian rheological behavior. The sludge loading significantly affected the fluid hydrodynamics and mass transfer. With an increase in the UG and P/VL, the ε and kLa increased, and the tm, decreased. The ε, kLa, and tm, were influenced dramatically as the flow regime changed from homogeneous to heterogeneous patterns. The proposed mathematical models predicted the experimental results well under experimental conditions, indicating that the UG, P/VL, and μap had significant impact on the tm, ε, and kLa. These models were able to give the tm, ε, and kLa values with an error around ±8%, and always less than ±10%. © 2005 Wiley Periodicals, Inc.
A general description of detachment for multidimensional modelling of biofilms
Authors: Xavier Joao de Bivar , Picioreanu Cristian , van Loosdrecht Mark C.M. 
Published: May 2005

AbstractA general method for describing biomass detachment in multidimensional biofilm modelling is introduced. Biomass losses from processes acting on the entire surface of the biofilm, such as erosion, are modelled using a continuous detachment speed function Fdet. Discrete detachment events, i.e. sloughing, are implicitly derived from simulations. The method is flexible to allow Fdet to take several forms, including expressions dependent on any state variables such as the local biofilm density. This methodology for biomass detachment was integrated with multidimensional (2D and 3D) particle‐based multispecies biofilm models by using a novel application of the level set method. Application of the method is illustrated by trends in the dynamics of biofilms structure and activity derived from simulations performed on a simple model considering uniform biomass (case study I) and a model discriminating biomass composition in heterotrophic active mass, extracellular polymeric substances (EPS) and inert mass (case study II). Results from case study I demonstrate the effect of applied detachment forces as a fundamental factor influencing steady‐state biofilm activity and structure. Trends from experimental observations reported in literature were correctly described. For example, simulation results indicated that biomass sloughing is reduced when erosion forces are increased. Case study II illustrates the application of the detachment methodology to systems with non‐uniform biomass composition. Simulations carried out at different bulk concentrations of substrate show changes in biofilm structure (in terms of shape, density and spatial distribution of biomass components) and activity (in terms of oxygen and substrate consumption) as a consequence of either oxygen‐limited or substrate‐limited growth. © 2005 Wiley Periodicals, Inc.
Developing high cell density fed‐batch cultivation strategies for heterologous protein production in Pichia pastoris using the nitrogen source‐regulated FLD1 Promoter
Authors: Resina David , Cos Oriol , Ferrer Pau , Valero Francisco 
Published: May 2005

AbstractA Pichia pastoris strain expressing a Rhizopus oryzae lipase gene under the transcriptional control of the promoter from the P. pastoris formaldehyde dehydrogenase 1 gene (PFLD) was utilized to study the feasibility of this expression system for recombinant protein production using methanol‐free fed‐batch high cell density cultivations. We have developed a simple and reliable fed‐batch strategy using the PFLD system based on the use of methylamine and sorbitol as nitrogen and carbon sources, respectively, for the induction phase. Three different fed‐batch fermentations were performed at three different constant growth rates, i.e., at a low growth rate (0.005/h), at an intermediate growth rate of (0.01/h), and at a constant residual sorbitol concentration of 8 g/L, i.e., allowing cells to grow at high (near µmax) growth rate (0.02/h). Important differences were observed between the lower and higher growth rate cultivation phases in terms of specific production rate (qp) profiles. In all three cases, maximum qp were reached soon after the start of the induction phase; after that maximum, an exponential decrease reaching final values close to zero were observed, except for the cells growing at near µmax. The best results in terms of YP/X, productivity and specific productivity were obtained when the microorganism was growing at the highest growth rate. Furthermore, such results were significantly better in relation to those obtained with the PAOX‐based system expressing the same protein. © 2005 Wiley Periodicals, Inc.
A continuous culture apparatus for the microbial utilization of hydrogen produced by electrolysis of water in closed‐cycle space systems
Authors: Foster John F. , Litchfield John H. 
Published: May 2005

AbstractTwo sources of oxygen for man in closed‐cycle space system environment have been considered in previous studies: (1) photosynthesis using algae, and (2) electrolysis of water. The latter system appears to be the most promising from the standpoints of energy and weight requirements and ability to operate in a zero gravity field. The surplus hydrogen produced by the electrolysis of water may be utilized together with waste carbon dioxide, part of the oxygen, and waste urea by bacteria of the genus Hydrogenomonas to produce cellular protein which might be used as a source of food. A continuous culture system for the propagation of hydrogen‐fixing bacteria consists of a baffled borosilicate glass culture vessel provided with an impeller, a reservoir vessel for the culture medium, and an overflow vessel for collecting the bacterial cells removed from the culture vessel. Complete feedback control of all parameters affecting growth can be provided by hydrogen, oxygen, and carbon dioxide sensors, and a pH electrode in the culture medium. In addition, total pressure is monitored. Cell density is controlled in the optimum range by means of a photoelectric cell which dictates the amount of fresh medium to be added and the amount of cells to be removed. Operating data indicate that some of the key parameters are the ratio of hydrogen, oxygen, and carbon dioxide in solution. The harvested bacterial substance is high in protein, which contains all the essential amino acids.
Enzymatic brominatioin of the thiazole ring
Authors: Neidleman S. L. , Cohen A. I. , Dean L. 
Published: May 2005

AbstractBromination of the thiazole ring by the enzyme chloroperoxidase, produced by the fungus Caldariomyces fumago, was demonstrated. Both 2‐acetoacetamido‐4‐methylthiazole and 2‐acetamidothiazole were brominated on C‐5 of the thiazole ring in the presence of chloroperoxidase, bromide, and hydrogen peroxide in 0.06 M Phosphate solution at pH 3.0. No reaction occurred in the absence of enzyme.