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  • Springer  (126)
  • 2000-2004  (126)
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  • 1
    ISSN: 1432-1327
    Keywords: Metal substitution Cerium binding Lactoferrin Crystal structure Transferrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Proteins of the transferrin family play a key role in iron homeostasis through their extremely strong binding of iron, as Fe3+. They are nevertheless able to bind a surprisingly wide variety of other metal ions. To investigate how metal ions of different size, charge and coordination characteristics are accommodated, we have determined the crystal structure of human lactoferrin (Lf) complexed with Ce4+. The structure, refined at 2.2 Å resolution (R=20.2%, R free=25.7%) shows that the two Ce4+ ions occupy essentially the same positions as do Fe3+, and that the overall protein structure is unchanged; the same closed structure is formed for Ce2Lf as for Fe2Lf. The larger metal ion is accommodated by small shifts in the protein ligands, made possible by the presence of water molecules adjacent to each binding site. The two Ce4+ sites are equally occupied, indicating that the known difference in the pH-dependent release of Ce4+ arises from a specific protonation event, possibly of the His ligand in one of the binding sites. Comparing the effects of binding Ce4+ with those for the binding of other metal ions, we conclude that the ability of transferrins to accommodate metal ions other than Fe3+ depends on an interplay of charge, size, coordination and geometrical preferences of the bound metal ion. However, it is the ability to accept the six-coordinate, approximately octahedral, site provided by the protein that is of greatest importance.
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  • 2
    ISSN: 1572-9591
    Keywords: Fusion energy ; international collaboration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This report was prepared by a Working Group at the request of the U.S. Department of Energy, Office of Fusion Energy Sciences in 1997. The report addresses technical opportunities for mutually beneficial collaboration between the United States and other international fusion research programs. A number of outstanding opportunities are discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 51 (2000), S. 166-172 
    ISSN: 1432-1432
    Keywords: Key words: Homoplasy — Microsatellites — Microsatellite evolution — Allele evolution — Apodemus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Microsatellite length variation was investigated at a highly variable microsatellite locus in four species of Apodemus. Information obtained from microsatellite allele sequences was contrasted with allele sizes, which included 18 electromorphs. Additional analysis of a 400-bp unique sequence in the flanking region identified 26 different haplotype sequences or ``true'' alleles in the sample. Three molecular mechanisms, namely, (1) addition/deletion of repeats, (2) substitutions and indels in the flanking region, and (3) mutations interrupting the repeat, contributed to the generation of allelic variation. Size homoplasy can be inferred for alleles within populations, from different populations of the same species, and from different species. We propose that microsatellite flanking sequences may be informative markers for investigating mutation processes in microsatellite repeats as well as phylogenetic relationships among alleles, populations, and species.
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  • 4
    ISSN: 1573-4846
    Keywords: fluorescence ; multidomain xerogels ; high-temperature processing ; fluorophore accessibility ; lifetimes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel processing methods offer novel pathways for tailoring glasses. Amongst the issues that have received the least attention are the effects of the curing temperature on the behavior and photophysics of a dopant molecule sequestered within a sol-gel-derived xerogel. Of particular interest to our group are the effects of processing variables on the ability of a dopant molecule, that is sequestered within a xerogel glass, to be accessed by an analyte and the distribution of the dopant sites within the xerogel. The thermal stability of the luminophore tris(4,7′-diphenyl-1,10′-phenanthroline) ruthenium (II) ([Ru(dpp)3]2+) provides a convenient way to address these issues and develop an understanding of how one might best exploit curing temperature to construct improved chemical sensors. This paper focuses on quantifying how the film curing temperature affects the spectroscopy and O2 quenching of ([Ru(dpp)3]2+) sequestered within sol-gel-derived xerogel thin films. Our quenching data on films once they have been cured demonstrate that there is a dramatic increase in the sensitivity of the ([Ru(dpp)3]2+) molecules to O2 quenching when the films have been cured at elevated temperatures. This arises primarily because there are two main types of ([Ru(dpp)3]2+) microenvironments within the glass and higher temperature curing leads to an increase in the bimolecular quenching rate between O2 and ([Ru(dpp)3]2+). This is accomplished as follows. Below a curing temperature of 100–150°C, ∼15% of the xerogel-doped ([Ru(dpp)3]2+) molecules are not accessed to any detectable degree by the O2 molecules during the ([Ru(dpp)3]2+) excited-state luminescence lifetime. However, as the xerogel is cured at or above 150°C, residual silanol-bound waters (or other impurities) dissociate from the xerogel and those ([Ru(dpp)3]2+) molecules that were initially inaccessible become accessible to O2. The dissociation of these water molecules, plus other events, also causes the originally inaccessible ([Ru(dpp)3]2+) population to ultimately exhibit a quenching rate that is greater than the fraction of initially accessible ([Ru(dpp)3]2+) molecules that were formed under ambient curing conditions.
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  • 5
    ISSN: 1573-4846
    Keywords: xerogels ; pyrene ; decay associated spectra ; oxygen quenching ; multiple domain types
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Steady-state and time-resolved fluorescence spectroscopy are used to determine the local microheterogeneity surrounding pyrene molecules sequestered within tetramethylorthosilicate-derived xerogels. After compensation for the intrinsic background emission from the xerogel, we find that the pyrene intensity decay kinetics are best described by a two-term rate law. This is consistent with the pyrene molecules distributing primarily into two microenvironments. Under ambient conditions, the individual pyrene microenvironments exhibit excited-state fluorescence lifetimes that differ by ∼100 ns. However, the pyrene I1 to I3 band ratios that are associated with each microenvironment are statistically equivalent to one another. These results show that the local dipolarity surrounding these pyrene microenvironments are similar, but the decay rates associated with each microenvironment are very different. The longer-lived pyrene species (Environment #1) constitutes ∼1/2 of the total fluorescence and it exhibits an O2 quenching sensitivity (Ksv1) of (5.19 ± 0.52 × 10−3 %O2 −1 and a bimolecular quenching constant (kq1) of (2.30 ± 0.23) × 104 %O2 −1 s−1. Environment #2, associated with the shorter-lived pyrene species, exhibits an O2 quenching sensitivity (Ksv2) of (2.31 ± 0.16) × 10−2 %O2 −1 and a bimolecular quenching constant (kq2) of (2.11 ± 0.23) × 105 %O2 −1 s−1. These results are interpreted as follows: Environment #1 consists of pyrene molecules sequestered within a relatively rigid siloxane network wherein non-radiative decay pathways are lessened, but these pyrene molecules are not quenched readily by O2. Environment #2 consists of pyrene molecules adsorbed onto surface silanols within the xerogel. These pyrene molecules are quenched by the silanols and they are simultaneously more accessible to O2 compared to Environment #1.
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  • 6
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thermal decomposition and electrical conductivity of oxide cathode emission materials used for cathode ray tubes (CRTs) have been studied under different heat treatment conditions for commercial sprayed cathode systems based on barium-strontium carbonate precursors. Conversion of the carbonate precursor commenced at temperatures above approximately 700 K in vacuum, evidenced by increases in conductivity, however, the rate of the conversion reaction increased dramatically as the temperature was increased. The corresponding chemical and microstructural changes have also been investigated by thermo-gravimetric analysis (TGA) and scanning electron microscopy (SEM), with multiple decomposition stages identified corresponding to the conversion of the carbonate precursor and separate activation steps associated with the reaction of barium oxide with the Mg and Al activating agents in the nickel cathode substrate. © 2000 Kluwer Academic Publishers
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  • 7
    ISSN: 1573-4919
    Keywords: transacylase ; platelet activating factor ; lysophospholipid ; lysophospholipase ; free fatty acid ; neuronal nuclei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract CoA-independent transacylase activities generating alkylacylglycerophosphocholine (AAGPC) from alkylglycerophosphocholine (1-alkyl GPC) were considerably enriched in neuronal nuclei isolated from rabbit cerebral cortex. Specific nuclear transacylation activities were 13 times the corresponding microsomal values. Several lysophospholipids, notably 1-acyl glycerophosphocholine (1-acyl GPC), 1-alkenyl GPC and 1-alkenyl GPE (1-alkenyl glycerophosphoethanolamine) inhibited the transacylation of 1-alkyl GPC. The inhibitory effects of 1-acyl GPC were seen in the presence of MAFP (methyl arachidonoylfluorophosphonate) or free oleate, compounds that inhibit neuronal nuclear lysophospholipase. When neuronal nuclei were preincubated with 1-alkyl GPC, the radioactive AAGPC product served as donor in transacylation reactions, to generate 1-alkyl GPC. In these nuclear reactions, 1-palmitoyl GPE and 1-palmitoyl GPC appeared to be poor acceptor substrates, when compared with corresponding 1-alkyl and 1-alkenyl analogues. The presence of free oleate or MAFP in the reactions containing 1-acyl GPC boosted the release of 1-alkyl GPC from AAGPC. These observations are of particular relevance to brain ischemia in which lysophospholipid, free fatty acid, and platelet-activating factor (PAF) levels rise dramatically. PAF can be made by the nuclear acetylation of 1-alkyl GPC, which is formed by nuclear transacylation mechanisms. Yet transacylase also removes 1-alkyl GPC, and thus this enzyme activity can regulate 1-alkyl GPC availability. Our observations indicate that lysophospholipids promote the formation of 1-alkyl GPC from nuclear AAGPC via transacylation, while free fatty acid likely prolongs the lifetime of 1-acyl lysophospholipids substrates by lysophospholipase inhibition. Similarly, once 1-alkyl GPC is formed, other lysophospholipids effectively compete with this 1-alkyl analogue and reduce its conversion back to AAGPC by transacylation. Free oleate, in this case, sustains 1-acyl lysophospholipid inhibitors of 1-alkyl GPC transacylation. Thus the cycle of transacylation may favour 1-alkyl GPC formation during ischemia, increasing levels of 1-alkyl GPC for nuclear acetylation reactions and PAF formation. The nuclear generation of PAF is of considerable importance as PAF can play regulatory roles in transcription events associated with inflammation.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Crop science 40 (2000), S. 655-658 
    ISSN: 1435-0653
    Keywords: K, Katepwa border G, Glenlea O, Oslo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Triticum aestivum L.) at Regina and Swift Current in 1995 and 1996. Interplot interference was evaluated with two spring wheat cultivars differing for height, Oslo (short) and Glenlea (tall). Interplot interference caused a 12% yield reduction in Oslo in the north–south rows, which was significantly greater than the 7% yield reduction in the east–west rows. The 7% yield reduction when spring-planted winter wheat separated the plots was significantly less than the 18% yield reduction when plots were adjacent. This study was conducted at fairly high latitudes and the conclusions should be restricted to higher latitudes. We conclude that spring wheat field trials with plots differing for height may have less interplot interference if rows are oriented east–west and separated with winter wheat.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Crop science 40 (2000), S. 7-12 
    ISSN: 1435-0653
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: H ) and in the subregion (H i ), and of the genotypic correlation between region and subregion means (r G′ ). r G′ depends on the magnitude of the genotype × subregion interaction (σ2 GS) relative to the genotypic variance (σ2 G). σ2 GS is the portion of the genotype × location interaction (σ2 GL) caused by local adaptation, rather than by random site-to-site variability in genotype means. Subdivision can increase heritability through the addition of σ2 GS to the numerator of H i , but this may be offset by reduced replication across locations within the subregion. Modeling using variance estimates from several cereal programs indicated that, unless σ2 GL is large relative to σ2 G and at least 30% of σ2 GL is due to σ2 GS, subdivision is unlikely to increase response. These results help explain the success of breeding programs that test broadly.
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  • 10
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The effects of pressure and oxygen fugacity (fO2) on trace element partitioning between pargasitic amphibole and alkali-basaltic melts have been determined at pressures from 1.5 to 2.5 GPa and oxygen fugacities at 2 log units above and below the nickel–nickel oxide buffer. Amphibole crystallization experiments were performed in a piston cylinder apparatus and partition coefficients between amphibole and quenched melt of large-ion-lithophile elements (LILE: Rb, Sr, Ba), high-field-strength elements (HFSE: Zr, Nb, Ta, Hf, U, Th) and rare-earth elements (REE: La to Lu; +Y) were measured with a LASER ablation inductively coupled plasma – mass spectrometer. Increasing pressure from 1.5 to 2.5 GPa at similar temperatures and approximately constant fO2 increases D Rb but decreases D Zr and D Hf and D REE (D La, D Ce, D Pr). An empirical relationship was observed between D Zr and (Ti/Al)M2 in the amphibole, which can be described by: Increasing the fO2 by ∼4 log units (∼NNO–2.0 to ∼NNO+2.2) at similar temperatures and constant pressure increases D Ba and D Nd but decreases D Ti. An increase in pressure or fO2 decreases the maximum partition coefficient (D o ), the Young's modulus (E) and the optimum ionic radius (r o ) of the A-, M2- and M4-lattice sites. The calculated r o values from the monovalent cations (Na, K, Rb) in the A site and the quadrivalent cations (Ti, Hf, Zr) in the M2 lattice sites suggests that amphiboles crystallized from alkaline basalt material have smaller 〈A-O〉 and 〈M2-O〉, mean bond-lengths than those formed from pargasitic materials at identical pressures and fO2's. The measured partition coefficients were used to calculate trace element concentrations in melts formed by partial melting of amphibole-bearing peridotite. This modeling demonstrates those changes in either the pressure or fO2 of melting can exert a significant effect on Rb/HFSE ratios in the melts and thus help explain the wide variations of these ratios sometimes observed in basaltic rock suites.
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