bluuebunny/crossref_metadata_2025 huggingface dataset:
Constrained ferroelectricity in the (001)-textured superlattices of PbZrO3∕BaZrO3
Authors: Wu Tai-Bor , Hung Cheng-Lung
Published: March 2005

A constrained ferroelectricity is found in the (001)-textured PbZrO3∕BaZrO3 superlattice films having an average composition of (Pb0.75Ba0.25)ZrO3, which is characterized by the linear dependence of remanent polarization (Pr) and coercive field (Ec) on the applied voltage and its stability against temperature change up to 100°C. A model based on equilibrium of electrostatic energy in dielectric stressing of the superlattice and polarization switching in the ferroelectric sublayer is proposed. The dielectric constant evaluated from a fitting of the measured Pr and Ec relations to the model is consistent to that obtained from impedance measurement. The thermal stability of this “linear” ferroelectricity can be also explained by the temperature-insensitive permittivity of the superlattice films, according to the proposed model.
Oxygen vacancy migration and time-dependent leakage current behavior of Ba0.3Sr0.7TiO3 thin films
Authors: Meyer R. , Liedtke R. , Waser R.
Published: March 2005

The leakage current response of high-permittivity columnar-grown (Ba,Sr)TiO3 thin films has been studied at elevated temperatures under dc load. We observe a thermally activated current prior to the onset of the resistance degradation with an activation energy of EA=1.1eV. A point defect model is applied to calculate the migration of electronic and ionic defects under the dc field as well as the current response of the system. We find that the peak in current is not caused by a space-charge-limited transient of oxygen vacancies, but related to a modulation of the electronic conductivity upon oxygen vacancy redistribution. Furthermore, we show that after the redistribution of electronic and ionic defects, no further increase in conductivity takes place in the simulation.
Postgrowth annealing of (Ga,Mn) As under As capping: An alternative way to increase TC
Authors: Adell M. , Ilver L. , Kanski J. , Stanciu V. , Svedlindh P. , Sadowski J. , Domagala J. Z. , Terki F. , Hernandez C. , Charar S.
Published: March 2005

In situ postgrowth annealing of (Ga,Mn)As layers under As capping is adequate for achieving high Curie temperatures (TC) in a similar way as ex situ annealing in air or in N2 atmosphere practiced earlier. Thus, the first efforts give an increase of TC from 68 to 145 K after 2 h annealing at 180 °C. These data, in combination with lattice parameter determinations and photoemission results, show that the As capping acts as an efficient sink for diffusing Mn interstitials.
Resonant x-ray scattering from a magnetic multilayer reflection grating
Authors: Michez L.-A. , Marrows C. H. , Steadman P. , Hickey B. J. , Arena D. A. , Dvorak J. , Zhang H.-L. , Bucknall D. G. , Langridge S.
Published: March 2005

We report the results of soft x-ray resonant magnetic scattering experiments conducted on Co∕Ru magnetic multilayers patterned into a reflection grating. Sample magnetization dependent scans of the in-plane wave vector transfer were performed to probe the relationship between the lateral physical and magnetic structures. Different Fourier components were found to dominate the sum and difference of these spectra, corresponding to different lateral wave forms for the structure-structure and structure-magnetism correlations.
Experimental demonstration of the slow group velocity of light in two-dimensional coupled photonic crystal microcavity arrays
Authors: Altug Hatice , Vučković Jelena
Published: March 2005

We recently proposed two-dimensional coupled photonic crystal microcavity arrays as a route to achieve a slow-group velocity of light (flat band) in all crystal directions. In this letter we present the experimental demonstration of such structures with a measured group velocity below 0.008c and discuss the feasibility of applications such as low-threshold photonic crystal lasers with increased output powers, optical delay components, and sensors.
Quantum cascade lasers with lateral double-sided distributed feedback grating
Authors: Golka S. , Pflügl C. , Schrenk W. , Strasser G.
Published: March 2005

Midinfrared single mode emission, up to 20°C, for a distributed feedback structure consisting of lateral index variation on both sides of a rib waveguide is achieved on a quantum cascade laser. Fabrication was made possible by a high density plasma process developed for high aspect ratio etching of GaAlAs∕GaAs structures. A lateral grating considerably enhances design freedom by decoupling the vertical waveguide structure from the grating strength. The grating coupling, now being mainly determined by waveguide width, can then be exploited for device applications.
Hydrogen sensing properties of a Pt-oxide-Al0.24Ga0.76As high-electron-mobility transistor
Authors: Cheng Chin-Chuan , Tsai Yan-Ying , Lin Kun-Wei , Chen Huey-Ing , Liu Wen-Chau
Published: March 2005

The interesting hydrogen sensing performances of a Pt-oxide-AlGaAs (MOS) high electron mobility transistor (HEMT) are studied and demonstrated. The effects of hydrogen adsorption on device performances such as the threshold voltage shift ΔVth, drain saturation current variation ΔIDS, and transient response are presented. ΔVth and ΔIDS decreased with increasing operating temperature. This suggests that, at higher temperature, less hydrogen atoms diffuse through the Pt bulk and reach the interface between the Pt metal and oxide layer resulting from the relatively faster formation rate of hydroxyl on the Pt surface. The response curves of the studied Pt-AlGaAs MOS HEMT show various profiles at different temperatures. The influences of hydrogen concentration and temperature on the interface sites occupied by adsorbed atoms are also studied.
Genomic imprinting of XX spermatogonia and XX oocytes recovered from XX↔XY chimeric testes
Authors: Isotani Ayako , Nakanishi Tomoko , Kobayashi Shin , Lee Jiyoung , Chuma Shinichiro , Nakatsuji Norio , Ishino Fumitoshi , Okabe Masaru
Published: March 2005

We produced XX↔XY chimeras by using embryos whose X chromosomes were tagged with EGFP (X*), making the fluorescent green female (XX*) germ cells easily distinguishable from their nonfluorescent male (XY) counterparts. Taking advantage of tagging with EGFP, the XX* “prospermatogonia” were isolated from the testes, and the status of their genomic imprinting was examined. It was shown that these XX cells underwent a paternal imprinting, despite their chromosomal constitution. As previously indicated in sex-reversal XXsxr testes, we also found a few green XX* germ cells developed as “eggs” within the seminiferous tubules of XX*↔XY chimeric testes. These cells were indistinguishable from XX* prospermatogonia at birth but resumed oogenesis in a testicular environment. The biological nature of the “testicular eggs” was examined by recovering the eggs from chimeric testes. The testicular eggs not only formed an egg-specific structure, the zona pellucida, but also were able to fuse with sperm. The collected testicular eggs were indicated to undergo maternal imprinting, despite the testicular environment. The genomic imprinting did not always follow the environmental conditions of where the germ cells resided; rather, it was defined by the sex that was chosen by the germ cells at early embryonic stage.
The Concept of Employability
Authors: McQuaid Ronald W. , Lindsay Colin
Published: March 2005

The concept of 'employability' plays a crucial role in informing labour market policy in the UK, the EU and beyond. This paper analyses current and previous applications of the term and discusses its value as an exploratory concept and a framework for policy analysis. It then traces the development of the concept, discusses its role in current labour market and training strategies (with particular reference to the UK) and seeks to identify an approach to defining employability that can better inform labour market policy, by transcending explanations of employment and unemployment that focus solely on either supply-side or demand-side factors. Although the literature offers a range of definitions of 'employability', many policy-makers have recently used the term as shorthand for 'the individual's employability skills and attributes'. It is argued that this 'narrow' usage can lead to a 'hollowing out' of the concept of employability. The paper concludes by presenting a broad framework for analysing employability built around individual factors, personal circumstances and external factors, which acknowledges the importance of both supply- and demand-side factors.
Employability, Skills Mismatch and Spatial Mismatch in Metropolitan Labour Markets
Authors: Houston Donald
Published: March 2005

The skills mismatch and spatial mismatch perspectives are often presented as competing explanations of the spatial distribution of unemployment within metropolitan areas. This paper argues that the spatial mismatch hypothesis addresses some of the shortcomings of the skills mismatch perspective, while not denying the importance of skills mismatch. The development of the spatial mismatch hypothesis in the US is traced, before considering its relevance in the British context. A framework in which to conceptualise and reconcile skills mismatch and spatial mismatch within metropolitan areas is developed, incorporating the operation of local housing and labour markets as well as the role of commuting. The paper concludes by arguing that skills and spatial mismatches reinforce each other and that the concept of employability offers some potential to help understand how job searchers and employers make decisions in situations of skills and/or spatial mismatch. The implications for future research are highlighted.
Employing the Unemployed: Some Case Study Evidence on the Role and Practice of Employers
Authors: Devins David , Hogarth Terence
Published: March 2005

Whilst there has been extensive research into the supply-side causal factors of spatial mismatch there is comparatively little commentary or analysis of the demand side. This paper seeks to make a contribution to the literature with particular reference to the human resources practices of employers. A three-stage model of recruitment is used to identify employer practices which we argue can (unwittingly) contribute to labour market mismatch. We conclude that, if recruitment from among the unemployed is to play a part in filling skills shortages, attention needs to be placed not only on the recruitment processes of employers but also on their retention and internal employee development practices.
Bryophyte colonisation in experimental microcosms: the role of nutrients, defoliation and vascular vegetation
Authors: Aude E. , Ejrnæs R.
Published: March 2005

A three‐year multi‐factorial microcosm experiment simulating fertilisation, defoliation and the composition of vascular vegetation in a dry grassland succession was used to test four hypotheses concerning the establishment and survival of bryophytes in grassland vegetation. H1: bryophyte cover may be used to predict bryophyte species richness. H2: bryophyte richness is suppressed at high nutrient levels and promoted by defoliation of vascular plants. H3: species richness of bryophytes is influenced by the species composition of the vascular vegetation. H4: bryophyte species richness is negatively correlated with vascular plant biomass.

The relationship between bryophyte richness and bryophyte cover was found to follow the classical species‐area richness curve. Bryophyte species richness responded positively to defoliation and negatively to fertilisation. The species composition of vascular vegetation had no significant effect on bryophyte richness. Bryophyte species richness was lower at high vascular plant biomass and vascular plant dry weight above 400 g m−2 appeared fatal to bryophytes. At high nutrient levels, defoliation increased bryophyte richness, but defoliation did not fully compensate for the negative effect of fertilisation. The study reinforces the concern for short lived shuttle bryophytes in the agricultural landscape.
Native harvester ants threatened with widespread displacement exert localized effects on serpentine grassland plant community composition
Authors: Peters Halton A. , Chiariello Nona R. , Mooney Harold A. , Levin Simon A. , Hartley Anne E.
Published: March 2005

Seed‐harvesting ants can influence the abundance and distribution of plant species through both the selective harvesting of seeds and the construction of nutrient‐rich nest mounds, but the relative contributions of these two mechanisms have not been addressed by previous studies. Furthermore, the impact of ant seed harvesting in California serpentine grasslands remains unresolved because of divergent results from several previous experiments. This study investigates the influence of harvester ants on serpentine grassland plant species composition by examining two potential signatures of seed harvesting ants on plant community composition: species composition on versus off ant nest mounds, and species abundance as a function of distance from nest mounds. Of the 28 plant species identified in this study, 22 exhibited spatial patterns consistent with effects of seed harvesting, nest construction, or both. Although most species showed significant gradients in abundance with distance from a nest, there were no clear relationships between plant species distributions and previously reported harvester ant seed foraging patterns. Harvester ant nest mounds supported plant communities that were distinct from the surrounding serpentine grassland, with notably higher densities of legumes and invasive annual grasses. Comparison of our results with those of previous studies indicates that the patterns we observed are generally consistent over time, but affect more species and a larger fraction of the grassland than previously reported. Unaffected areas of the grassland seem likely to serve as important refuges for some plant species.
Sex ratio of Parus major and P. caeruleus broods depends on parental condition and habitat quality
Authors: Stauss Michael , Segelbacher Gernot , Tomiuk Jürgen , Bachmann Lutz
Published: March 2005

Brood sex ratio was studied in 88 families of Parus caeruleus (blue tit) and 95 families of P. major (great tit) in deciduous and mixed forest habitats differing in food availability. As a food specialist, the blue tit is expected to be more sensitive to the nutritional differences between the habitats than a food generalist such as the great tit. A shift of brood sex ratio towards males was detected for great tits in the high quality habitat, but there was no significant impact of parental condition or the number of nestlings. In contrast, brood sex ratio of blue tits was not affected by habitat quality. In blue tits, male condition correlated positively with a male‐biased sex ratio. Habitat quality, however, affected the body mass differences of male and female blue tit siblings, and nestlings developed differently. The low quality habitat had a negative effect on the sexual dimorphism of siblings in male‐biased broods, and the condition of offspring was bad. Nevertheless, sexual dimorphism cannot explain the differences between great and blue tits with respect to the correlation of sex ratio and individual condition.
A comparative study of body size and clutch size across the parasitoid Hymenoptera
Authors: Traynor Ruth E. , Mayhew Peter J.
Published: March 2005

Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the “fast‐slow continuum” in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross‐species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically‐based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.
Bootstrap methods for estimating spatial synchrony of fluctuating populations
Authors: Lillegård Magnar , Engen Steinar , Sæther Bernt‐Erik
Published: March 2005

We describe and examine methods for estimating spatial correlations used in population ecology. We base our analyses on a hypothetical example of a species that has been censured at 30 different locations for 20 years. We assume that the population fluctuations can be described by a simple linear model on logarithmic scale. Stochastic simulations is utilized to check how seven different ways of resampling perform when the goal is to find nominal 95% confidence intervals for the spatial correlation in growth rates at given distances. It turns out that resampling of locations performs badly, with true coverage level as low as 30–40%, especially for small correlations at long distances. Resampling of timepoints performs much better, with coverage varying from 80 to 90%, depending on the strength of density regulation and whether the spatial correlation is estimated for the response variable or for the error terms in the model. Assuming that the underlying model is known, the best results are achieved for parametric bootstrapping, a result that strongly emphasize the importance of defining and estimating a proper population model when studying spatial processes.
Spatial diversity in mitochondrial cytochrome c oxidase in house flies
Authors: Cummings M. A. , Krafsur E. S.
Published: March 2005

Abstract.  DNA sequence analysis at mitochondrial gene COI was surveyed in 293 house flies, Musca domestica Linneaus (Diptera: Muscidae), in 29 populations from North, Central and South America, Europe, Asia, Africa, and the Western Pacific. Nei's gene diversity index (HS) was 0.47, the chance that two randomly chosen flies have different COI haplotypes. Haplotype diversity was greater in the Old World (HS = 0.58) than the New World (HS = 0.31). The hierarchical partition of the total diversity indicated substantial differentiation at all levels (GST = 0.30), and highly structured populations. All pairwise estimates of gene flow between zoogeographical regions were less than 0.70 reproducing females per generation. The results are compared to those of a similar study based on the single‐strand conformation polymorphism method. Probable colonization scenarios for house flies into the New World are discussed and it is concluded that house flies are a recent addition to the fauna of the Western Hemisphere.
Population differentiation andWolbachiaphylogeny in mosquitoes of theAedes scutellarisgroup
Authors: Behbahani A. , Dutton T. J. , Davies N. , Townson H. , Sinkins S. P.
Published: March 2005

Abstract. Mosquito species of theAedes(Stegomyia)scutellaris(Walker) group (Diptera: Culicidae) are distributed across many islands of the South Pacific and include major regional vectors of filariasis, such asAedes polynesiensis(Marks). Analysis of populations ofAe. polynesiensisat the extremes of its range, from Fiji and from Moorea, French Polynesia, using the rDNA ITS2 (internal transcribed spacer 2) region and six microsatellite markers showed considerable genetic differentiation between them (FST = 0.298–0.357). Phylogenetic analysis of theWolbachiaendosymbionts in three members of the complex revealed that based on thewspgene they are all very similar and belong to theMelsubgroup of the A clade, closely related to theWolbachiastrain present in the gall waspCallyrhytis glandium(Giraud) (Hymenoptera: Cynipidae). By contrast they are only distantly related to the A‐cladeWolbachiainAedes albopictus(Skuse), a species closely allied to theAe. scutellarisgroup. There was very low differentiation between theWolbachiain the Moorea and Fiji populations ofAe. polynesiensis.
Iraq, Afghanistan and the War on“Terror”
Authors: Byman Daniel , Scheuer Michael , Lieven Anatol , Lang W. Patrick
Published: March 2005

The following is an edited transcript of the thirty‐eighth in a series of Capitol Hill conferences convened by the Middle East Policy Council. The meeting was held on January 11, 2005, in the Dirksen Senate Office Building, with Chas. W. Freeman, Jr., moderating.
Evaluating The Bush Menu for Change in the Middle East
Authors: Cantori Louis J. , Norton Augustus Richard , Rosefsky Wickham Carrie , Yaphe Judith S. , Hudson Michael C. , Davis Eric
Published: March 2005

These contributions were presented at a roundtable of the Conference Group on the Middle East, “Evaluating the Bush Menu for Change in the Middle East,” at the American Political Science Association Annual Meeting, Chicago, September 5, 2004.
Influence of Salts on RNA Synthesis by DNA‐Dependent RNA‐Polymerase from Escherichia coli
Authors: Fuchs E. , Millette R. L. , Zillig W. , Walter G.
Published: March 2005

The effect of salt concentration on RNA synthesis by DNA‐dependent RNA‐polymerase from Escherichia coli has been investigated. For a double stranded template the following influences are observed: (1) Free enzyme and enzyme bound to DNA, but not synthesizing RNA, are inhibited above an ionic strength of about 0.15. (2) The rate of RNA‐synthesis, by those enzyme molecules which have started RNA chains, is stimulated by increasing the salt concentration up to an optimum. Magnesium salts cause a larger stimulation than monovalent cations. However, the optimal effect always occurs at an ionic strength of about 0.36. (3) This stimulatory effect is distinguished from the cofactor function which requires only low concentrations of divalent cations (Mg2+, Co2+, Mn2+). (4) RNA synthesis stops at low ionic strength (<0.2) due to a first order inactivation of the synthesizing enzyme. At high ionic strength synthesis continues over many hours at a slowly decreasing rate. Raising the ionic strength after RNA synthesis has stopped at low ionic strength causes an immediate resumption of synthesis. Mg2+ and spermidine are most effective in this action. However, Co2+ and Mn2+ are unable to reactivate the enzyme once it has stopped.

With single stranded DNA as template neither a first order inactivation of synthesizing enzyme at low ionic strength nor a stimulation of RNA synthesis by monovalent salts is observed. The effect of divalent cations on enzyme activity can be due to their cofactor function.
Synchronized Yeast Cells
Authors: Eckstein H. , Paduch V. , Hilz H.
Published: March 2005

Homogenates and extracts of yeast cells (Saccharomyces cerevisiae) exhibit DNA polymeras activity as revealed by incorporation of labeled dATP into DNAase‐sensitive, RNAase‐resistent acid‐insoluble material, the incorporation being dependent on the presence of all four deoxynucleotide triphosphates and primer DNA.

Extracts from synchronized yeast cells exhibit DNA polymerase activity in an oscillating manner during the cell cycle, maximum activity being found just before the onset of DNA replication. Degradation and resynthsis, or transformation to an inactive “zymogen” are discussed as possible mechanisms of the oscillating behavior of polymerase activity.

X‐irradiation brings about a dissociation of DNA replication and oscillating appearance of the polymerase. Whereas DNA replication is temporarily delayed, the rhythmic appearance of the enzyme is unaffected. However, the height of the activity maxima remains unchanged until DNA is reduplicated again. The observations are discussed with regard to the apparent intactness of the DNA template functions and to the persistence of the sequential transcription of genes in the proliferation‐inhibited irradiated yeast cells.
Studies on Phytosterol Biosynthesis
Authors: Goad L. J. , Willams B. L. , Goodwin T. W.
Published: March 2005

By the use of thin layer chromatography, gas‐liquid chromatography, the Liebermann‐Burchard reaction and mass‐spectrometry, 4α,14α‐dimethyl‐Δ8,24(28)‐ergostadien‐3β‐ol (obtusifoliol) and cycloeucalenol have been demonstrated in grapefruit peel. Gas‐liquid chromatography has also revealed the presence of these compounds in several other plant tissues.
The Role of Free Amino Groups in the Blood Group Activity of M and N Mucoids
Authors: Lisowska E. , Morawiecki A.
Published: March 2005

The M and N blood group substances were treated with different amino‐group reagents, such as: acetic‐, succinic‐, and phthalic‐anhydrides, benzyloxycarbonylchloride, dinitrofluorobenzene, nitrous acid and O‐methyl‐isourea.

It was shown that htese reagents blocked or destroyed 2–4 free amino groups (mainly lysine ɛ‐NH2 groups) per one subunit of M or N blood group substance of mol. wt. 30,000. No other effects were found under the conditions used.

The blocking or decomposition of amino groups, connected with the loss of their positive charge, lowered the blood activity of M and N mucoids and did not decrease their activity towards phytoagglutinins and the inhibitory activity of viral hemagglutination. The guanidylation of amino groups did not destroy the blood group activity of M and N mucoids.
Investigations on the Reaction of Metals with Collagen in vivo
Authors: Adam M. , Fietzek P. , Kühn K.
Published: March 2005

The effect of treatment in vivo with gold thiosulphate on the skin collagen of normal and lathyritic rats has been investigated. While the neutral‐salt‐soluble collagen is not affected by gold thiosulphate, the insoluble collagen content is increased. The solubility in urea of the insoluble collagen is lowered. The lathyritic effect is partly reversed. The gold thiosulphate thus reacts with the insoluble collagen introducing additional cross‐links. The biosynthesis of collagen does not appear to be affected.
A Polyribonucleotide Containing Alternating → P = O and → P = S Linkages
Authors: Matzura H. , Eckstein F.
Published: March 2005

The enzymatic synthesis of the polyribonucleotide by the use of RNA polymerase is described. Snake venom and spleen phosphodiesterase degrade this polymer at a very slow rate compared to poly r(A—U). The dinucleotide resulting from digestion with pancreatic ribonuclease is resistant to spleen phosphodiesterase.
On the Interaction of Bovine Cobalt Carbonic Anhydrase with Sulfonamides
Authors: Lindskog S. , Thorslund A.
Published: March 2005

The pH‐dependence of the inhibition of cobalt carbonic anhydrase by three different sulfonamides has been measured employing p‐nitrophenyl acetate as substrate. The binding of these inhibitors is linked to two ionizing groups. One of these seems to be identical to the group in the enzyme previously shown to control the catalytic activity. The pK of the second group is characteristic for the individual inhibitor and agrees with pK‐values obtained by titration of the sulfonamides.

Sulfanilamide and the anionic inhibitor, NO3−, appear to compete for one binding site on the enzyme.

When the sulfanilamide inhibition of the CO2‐hydration activity was studied by the stopped‐flow method, some anomalous behavior was observed. From the initial part of the reactions, apparent noncompetitive inhibition was obtained. The rates increased over a short time period, however, to give essentially a competitive pattern. The results can be explained by assuming that the substrate and the inhibitor are competitive, but that equilibration is not immediately achieved due to a comparatively slow rate of dissociation of the inhibitor from the enzyme.

The apparent second order rate constant for the formation of the enzyme‐sulfanilamide complex has been estimated as 7 × 104 M−1 sec−1 at pH 7.9 and 25°. In the presence of CO2, the reaction is slower to an extent which is compatible with a competition for a common binding site.

A simple, though not unique, mechanism for the sulfonamide inhibition of bovine cobalt carbonic anhydrase, accounting for both rate and equilibrium data, implies the formation of the enzyme‐inhibitor complex through a direct reaction of the ionized sulfonamide with the inactive, acid form of the enzyme.
Purification and some Properties of Lysyl Ribonucleic Acid Synthetase from Escherichia coli
Authors: Waldenström J.
Published: March 2005

The lysyl ribonucleic acid synthetase from Escherichia coli has been purified to apparent homogeneity as judged from polyacrylamide gel electrophoresis and sedimentation velocity centrifugation. A molecular weight of 100,000 has been calculated for the enzyme.
Organization of Fatty Acid Oxidation in Rat Kidney Mitochondria
Authors: ROSSI C. R. , ALEXANDRE A. , SARTORELLI L.
Published: March 2005

Long‐chain fatty acids are oxidized by intact rat kidney mitochondria under experimental conditions which permit the location of three long‐chain acyl‐CoA synthesizing systems.

Oleate oxidation which is 2,4‐dinitrophenol‐insensitive and which is inhibited by arsenate and excess phosphate, is probably energized by GTP. The isolation of the GTP‐dependent acyl‐CoA synthetase from sonicated kidney mitochondria supports this hypothesis.

Oleate oxidation which is insensitive to phosphate and arsenate and requires oligomycin, utilizes “endogenous” ATP and is not linked to added carnitine.

The third oleate oxidation system requires added ATP, CoA and phosphate and depends on a carnitine‐linked transport mechanism.
The Phosphoinositide Inositolphosphohydrolase of Guinea‐Pig Intestinal Mucosa
Authors: ATHERTON R. S. , HAWTHORNE J. N.
Published: March 2005

Some properties of the phosphoinositide inositolphosphohydrolase of guinea‐pig intestinal mucosa supernatant fraction are described. The enzyme has an absolute requirement for metal ions, the most efficient activator being Ca2+. The pH optimum is 5.3 in acetate buffer and 5.9 in maleate; activity is higher in the latter. The effects of detergents and various reagents are described. Corn phosphatidyl inositol is hydrolysed faster than brain phosphatidyl inositol; the fatty acid compositions of these lipids have been compared. The enzyme is remarkably specific for the phosphoinositides. The composition of the enzyme preparation has been studied. The enzyme appears to be widely distributed in animal tissues.
Zur Bildung von Chinolinalkaloiden in Pflanzen
Authors: COBET M. , LUCKNER M.
Published: March 2005

Last year it was shown that the quinoline nucleus of the furoquinolines dictamnine and skimmianine is biogenetically derived from anthranilic acid and acetate. The labelling pattern indicates that the C‐atoms 4,12,5–8 and 9 and the nitrogen arise from anthranilic acid whilst C‐10 and C‐11 come from the carboxylic and the methyl group of acetic acid, respectively. Until now no intermediates of this biosynthetic pathway were known.

To proof the activity of 2‐amino‐benzoylacetic acid and its amide 2,4‐dihydroxyquinoline (both compounds are in a pH dependent equilibrium) as precursors of the furoquinolines we have synthesised 2,4‐dihydroxy‐3‐14C‐quinoline. After feeding this compound to plants of Ruta graveolens L. Kokusaginine (4,6,7‐trimethoxy‐furoquinoline) was isolated. The high incorporation rate which was found leads to the conclusion that 2,4‐dihydroxyquinoline (and 2‐amino‐benzoylacetic acid) are direct precursors of this alkaloid.
Vergleich verschiedener Modifikationen von Glutaminsynthetase aus Escherichia coli
Authors: LIESS K. , VARRICCHIO F. , MECKE D. , HOLZER H.
Published: March 2005

The preparation of three forms of glutamine synthetase from Escherichia coli is described: 1. active glutamine synthetase (GSa) from derepressed cells, grown on an ammonia free medium, 2. glutamine synthetase inactivated in vivo [GSb(vv)] by addition of ammonium salts to the culture medium, 3. glutamine synthetase inactivated in vitro [GSb(vt)] by the “inactivating enzyme” in the presence of ATP, Mg2+, and glutamine. GSa has a high activity in the glutamine synthetase reaction as well as in the glutamyl transferase reaction, whereas GSb(vv) and GSb(vt) have low activities in the glutamine synthetase reaction and high activities in the glutamyl transferase reaction. GSb(vv) and GSb(vt) behave similarly in catalytic properties and in feedback inhibition. There are no differences between the two preparations of GSb in the sedimentation in the ultracentrifuge, in electrophoresis on agar gel or polyacrylamide and in chromatography on DEAE cellulose. These results indicate, that GSb(vv) and GSb(vt) are identical. This leads to the conclusion, that the in vitro inactivation and the in vivo inactivation are caused by the same reaction. The sedimentation constants as well as the optical rotatory dispersion of GSa and of the two forms of GSb are identical. No separation of the three modifications of GS were achieved by chromatography on DEAE‐cellulose or by electrophoresis. The effects of allosteric effectors in the synthetase reaction are the same although GSb has in this reaction only 5–10% of the activity of GSa. As compared to GSa the two GSb preparations exhibit in the UV spectrum a shift of the absorption maximum to shorter wavelenghts.
Metal Content of Cysteamine Oxygenase
Authors: CAVALLINI D. , DUPRÉ S. , SCANDURRA R. , GRAZIANI M. T. , COTTA‐RAMUSINO F.
Published: March 2005

Cysteamine oxygenase has been analysed for the presence of metals, by spectrographic analysis, and X‐ray fluorescence. Iron, copper, and zinc have been found in the enzyme in the quantity accounting for 1 atom of each metal per molecule of enzyme.

Passage of the enzyme through a chelating resin column did not appreciable change the specific activity but the metal content was decreased below the value of one atom per molecule of enzyme. Possible explanations for this finding are suggested.

The effect of several chelating agents on enzymic activity has been studied. All the chelating agents assayed were found inhibitory when tested in suitable concentration. The highest inhibition was observed with 8‐hydroxyquinoline, diethyldithiocarbamate and o‐phenanthroline. KCN also was a good inhibitor.

It is concluded that cysteamine oxygenase is a metal‐containing enzyme and that the metals should play a functional role.
Myo‐Inositol, a Cofactor in the Biosynthesis of Stachyose
Authors: TANNER W. , KANDLER O.
Published: March 2005

In extracts from Phaseolvs vulgaris seeds an enzyme has been found which transfers the galactosyl moiety of galactinol to raffinose giving rise to stachyose and myo‐inositol.

Two tests to measure the enzyme activity are described.

The reaction is reversible. An equilibrium constant of approximately 4 has been determined for . The enzyme catalyzes exchange reactions between galactinol and myo‐[14C]inositol and between stachyose and [14C]raffinose. Specifically labeled galactinol and stachyose can be prepared in this way.

The Km values for galactinol and for the two best galactosyl acceptors, raffinose and melibiose, have been measured.

Besides the galactinol: raffinose‐6‐galactosyl transferase the extract of the seeds also contains an α‐galactosidase, which separates from the transferase during the purification. The transferase is strongly inhibited by p‐chloromercuribenzoate.

Ripening seeds contain an enzyme which catalyzes the reaction UDP‐galactose + myoinositol → galactinol + UDP. However, no direct transfer of galactose from UDP‐galactose to raffinose has been observed.

The physiological importance of the results is discussed.
Isolement, purification et quelques caractéristiques physicochimiques de deux β‐hexosidases du suc digestif d'Helix pomatia
Authors: GOT R. , MARNAY A.
Published: March 2005

Two enzymes, G1 et G2, that hydrolyse o‐nitrophenyl‐β‐d‐galactopyranoside (ONPG), were isolated from the digestive juice of the snail Helix pomatia. Preparation involved precipitation with 30 vol.‐% acetone at pH 5.4 and −12°, filtration on Sephadex G‐200, precipitation with 2.8 M ammonium sulfate, chromatography on CM‐cellulose for G1 and on DEAE‐sephadex for G2; yield is approximately 7% for G1 and 25% for G2 from total activity.

Pure enzymes were free from β‐glucuronidase and N‐acetyl‐glucosaminidase activities. Their homogeneity was established by criteria such as ultracentrifugation, immunoelectrophoresis and electrophoresis on cellulose acetate and in polyacrylamide or starch gel.

Enzymes had a carbohydrate content of about 15‐16%, with galactose, mannose, glucose, fucose and glucosamine, but without sialic acid. Isoelectric points and electrophoretic mobilities of the two enzymes were also similar, but migration on starch gel and sedimentation coefficients (respectively 6.4 S and 10.4 S) were different. They had no immunological identity.

The pH optima, in constant ionic strength 0.1 M sodium phosphate‐citric acid buffers, for hydrolysis of ONPG and lactose were respectively 5.4 for G1 and 5.2 for G2. Both enzymes attacked cellobiose, p‐nitrophenyl‐β‐d‐glucopyranoside and p‐nitrophenyl‐β‐d‐fucoside at the same pH as lactose or ONPG. Michaelis constants were determined by the method of Eadie. Values were lower for G2 than for G1.

Evidences were produced that β‐galactosidase and β‐glucosidase activities reside in a single protein.
The Fractionation of the Histones of Group F2(b) from Calf Thymus
Authors: JOHNS E. W.
Published: March 2005

The histones of group F2(b) have been fractionated by acetone precipitation and by column chromatography on carboxymethylcellulose at pH 9.

The acetone precipitation method enables F2(b), prepared on a large scale by extraction methods, to be further purified in bulk, the resulting product having 84% N‐terminal proline.

The column chromatography on carboxymethylcellulose at pH 9 has given 5 main fractions, two of which contain over 25% acidic amino acids (or their amides) and over 24% basic amino acids.
Structure sous‐unitaire de la thyroglobuline de mouton
Authors: LISSITZKY S. , ROLLAND M. , REYNAUD J. , SAVARY J. , LASRY S.
Published: March 2005

Full reduction of the disulfide bridges of pure 19 S sheep thyroglobulin has been obtained by 2‐mercaptoethanol in 0.1 M Tris‐acetate pH 8.6 containing 8 M urea followed by alkylation (iodoacetate or iodoacetamide) of the thiol groups formed.

The S‐carboxymethylderivative is soluble only in the presence of concentrated urea or guanidine hydrochloride. Dissolved in the presence of 5 M or 6 M guanidine at pH 7.0 or 8.6 it sediments in the ultracentrifuge as a single homogeneous boundary.

In 5 M or 6 M guanidine at 20° and 25° the sedimentation constants extrapolated to zero concentration are: s°20, guan 6 M= 1.2 S; s°25, guan 5 M= 2.0 S. The values for the diffusion constant and for the intrinsic viscosity are: D°25, guan 5 M= 3.4; 100 [η]20, guan 6 M= 85; 100 [η]25, guan 5 M= 78.

Using these values, 0.705 for v and the values of s/D determined by equilibrium or approach‐to‐equilibrium sedimentation, the following molecular weight have been calculated: M1= 80 × 103 or 85 × 103 (equilibrium sedimentation), M2= 81 × 103 (approach‐to‐equilibrium in 0.017 M SDS at pH 8.6), M3= 70 × 103 (Svedberg equation). The molecular weight computed from the values of s and [η] in 5M and 6M guanidine were 160 × 103 and 114 × 103 respectively.

By gel filtration on Sephadex G‐200 in 0.1 M Tris‐acetate pH 8.6 containing 0.017 M sodium dodecylsulphate, the S‐carboxymethyl derivative of thyroglobulin is more retarded than γ‐globulin 7 S and serumalbumin. After correction for protein‐bound sodium dodecylsulphate the apparent molecular weight calculated for S‐carboxymethyl thyroglobulin by gel filtration agrees fairly well with the molecular weight (80 × 103) computed from the hydrodynamic properties. A similar value has been obtained by gel filtration on Sephadex G‐200 in Tris‐acetate 0.1 M pH 8.6 containing 5 M guanidine.

The discrepancy between the values of the molecular weight computed from the measurements of s and [η] on the one hand and by the measurement of s/D or s and D on the other hand is discussed in relation to data in the literature.

It is concluded that the 12 S subunit of thyroglobulin is most probably constituted by two different peptide chains (A = B = 80 × 103) in a proportion which remains to be determined.
Erreurs dans l'incorporation de certains amino‐acides après bromuration des RNA de transfert de levure
Authors: BAKES J. , EHRESMANN C. , BEFORT N. , WEIL J. H. , EBEL J. P.
Published: March 2005

Some amino acids, such as isoleucine, valine, glutamic acid and lysine, which normally are not transferred from the corresponding aminoacyl‐tRNA's into polypeptides in the presence of poly U, are transferred when they are carried by brominated tRNA's. These errors are also observed in the presence of natural messenger RNA's: In a non‐preincubated cell‐free system which has been saturated with normal isoleucyl‐tRNA, the addition of bromiated isoleucyl‐tRNA produces an extra incorporation of isoleucine, whereas the addition of normal isoleucyl‐tRNA does not cause any further incorporation of isoleucine. These experiments suggests that the brominated isoleucyl‐tRNA molecules can recognize other triplets than those which normally code for the aminoacid isoleucine.

In a non‐preincubated cell‐free system, in the presence of natural messenger RNA, there is a competition between normal phenylalanyl‐tRNA and brominated isoleucyl‐tRNA, and this suggests that the brominated isoleucyl‐tRNA molecules are able to recognize the UUU or UUC triplets. In the formation of the complex aminoacyl‐tRNA‐ribosomes‐poly U, the incorporation of brominated isoleucyl‐tRNA in the complex is greater than that of normal isoleucyl‐tRNA, and this is also in favor of the recognition of the UUU code words by brominated isoleucyl‐tRNA.
On the Fatty Acid and Hydrocarbon Hydroxylation in Rat Liver Microsomes
Authors: DAS M. L. , ORRENIUS S. , ERNSTER L.
Published: March 2005

The hydroxylation of heptane and laurate in rat liver microsomes has been studied with respect to catalytic components involved in the two reactions. The results have been compared with those obtained with aminopyrine and testosterone as substrates for microsomal hydroxylation. The hydroxylation of all four substrates was found to be inhibited by the oxidized form of cytochrome c and by carbon monoxide, as well as by NADP+ in a competitive manner. Treatment of rats with phenobarbital in vivo resulted in a similar increase in the rate of hydroxylation of all four substrates as measured with the isolated liver microsomes. It is concluded that the hydroxylation of heptane and laurate as well as the oxidative demethylation of aminopyrine and hydroxylation of testosterone proceeds by way of a common microsomal hydroxylation enzyme system involving the NADPH‐cytochrome c reductase and the cytochrome P‐450. The broad action spectrum of this enzyme system is discussed, and the possibility is considered that fatty acids like laurate, in addition to certain steroid hormones, may serve as the physiological substrates for this enzyme system.
Myeloperoxidase of Human Leukaemic Leucocytes
Authors: ZGLICZYŃSKI J. M. , STELMASZYŃSKA T. , OSTROWSKI W. , NASKALSKI J. , SZNAJD J.
Published: March 2005

Myeloperoxidase was isolated from leucocytes obtained from the blood of patients suffering from chronic granulocytic leukaemia. The enzyme was purified 850 fold and was homogeneous in ultracentrifuge and free boundary electrophoresis. The molecular weight of the enzyme was found to be about 160,000.

The enzyme forms a spectrally characteristic complex with hydrogen peroxide with absorption maximum at 458 mμ. The spectrum of the native enzyme has absorption maxima at 430 and 570 mμ. The reduced enzyme is characterized by a spectrum with absorption maxima at 472 and 637 mμ.

The investigated myeloperoxidase catalysed oxidation of amino acids by hydrogen peroxide. Products of the oxidation of amino acids were ammonia, carbon dioxide, and an aldehyde corresponding to the oxidized amino acid. The observed reaction of deamination and decarboxylation is activated by chloride ions. In the presence of the chloride ions the optimum of the reaction is shifted toward the higher pH values.

The velocity of the reaction was found to be dependent on the concentration of the amino acid studied. Km values for various amino acids increased in the range 3.4 × 10−4 to 10−3 M in proportion to rising hydrophobic properties of the substrates. Taurine was found to be a competitive inhibitor in the examined reaction, and Ki values were in the range of 2 to 3 × 10−4 M, for different amino acids.
Inhibition Studies on Liver Alcohol Dehydrogenase
Authors: EVANS N. , RABIN B. R.
Published: March 2005

The rate of reaction of liver alcohol dehydrogenase with iodoacetamide is independent of pH between pH 6–10. Orthophenanthroline, ADP‐ribose and ADP protect the enzyme against alkylation. For iodoacetate, the rate of alkylation decreases with increasing pH over the range 7–9 and reflects the titration of a group with a pK of 7.9. Imidazole enhances the rate of alkylation by both iodoacetamide and iodoacetate and renders the rate of alkylation by iodoacetate pH independent. The interactions of ADP‐ribose and imidazole with the enzyme are shown to be independent of each other. A mechanism is suggested in which the substrate and coenzyme are simultaneously bound to zine. Mechanisms for the activation of both reaction partners are presented.
Energy Requirements in the Incorporation of Choline by Isolated Rat Liver Mitochondria
Authors: BYGRAVE F. L. , KAISER W.
Published: March 2005

Optimal concentrations of ATP, CTP and ADP for the incorporation of 14C‐labelled choline into phospholipid by isolated rat liver mitochondria were 0.7 mM, 0.25 mM and 1.0 mM respectively. Higher concentrations markedly depressed the incorporation. Substitution of CTP for other nucleotide triphosphates led to lower rates of incorporation.

Inhibitors of electron transport and of oxidative phosphorylation inhibited the respiration‐supported but not the ATP‐supported incorporation of choline. It is concluded that high energy intermediates of oxidative phosphorylation are not obligatory for the incorporation process.
Incorporation of Glucose into an Insoluble Polyglycoside during Oscillatory Controlled Glycolysis in Yeast Cells
Authors: Betz A. , Hinrichs R.
Published: March 2005

In the first few minutes of oscillatory controlled glycolysis yeast cells convert 50% of all glucose taken up into ethanol and glycerol, and incorporate 80–90% of the rest into some in‐soluble polyglycoside.

Glucose uptake in glycolysing yeast cells is a pulsatory process which is in phase with fruc‐tose‐1,6‐diphosphate synthesis. The concentration of UDPG, an intermediate in polyglucoside synthesis, is oscillating in phase with glucose‐6‐phosphate.

The cells use 80–90% of all ATP synthesized in glycolysis for uptake and storage of glucose.