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  • Springer  (80)
  • Oxford University Press  (22)
  • 2000-2004  (102)
  • 2004  (35)
  • 2000  (67)
  • 1
    Electronic Resource
    Electronic Resource
    Metal substitution in transferrins: specific binding of cerium(IV) revealed by the crystal structure of cerium-substituted human lactoferrin (2000)
    Springer
    JBIC 5 (2000), S. 692-698 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750000157
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  • 2
    Electronic Resource
    Electronic Resource
    Technical Opportunities for International Collaborations by the U.S. Fusion Program (2000)
    Springer
    Journal of fusion energy 19 (2000), S. 65-79 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012281826821
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  • 3
    Electronic Resource
    Electronic Resource
    Variation of pollen limitation in the early flowering Mediterranean geophyte Narcissus assoanus (Amaryllidaceae) (2000)
    Springer
    Oecologia 124 (2000), S. 529-535 
    Details
    ISSN: 1432-1939
    Keywords: Key words Fruit and seed set ; Narcissus assoanus ; Pollen limitation ; Reproductive ecology ; Seed:ovule ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A recent literature review indicates that pollen limitation of female fertility is a common feature of flowering plants. Despite the ecological and evolutionary significance of pollen limitation, most studies have only examined fertility in a single population at one time. Here we investigate pollen limitation of fruit and seed set in five populations of Narcissus assoanus, a self- sterile, insect-pollinated geophyte, over 2–3 years in southern France. In common with many early spring flowering plants, pollinator visitation to N. assoanus is often infrequent. Supplemental hand-pollination of flowers with outcross pollen significantly increased overall fruit and seed set by 11% and 19%, respectively. Four of the five populations experienced some pollen limitation during the study. For a given year, there was significant variation in pollen limitation among populations. Two of the populations were pollen limited in one year but not in other years in which they were studied. Seed:ovule ratios for open- and hand-pollinated flowers averaged 0.29 and 0.33, respectively. While hand pollination significantly increased the seed:ovule ratio, the low value obtained indicates that the majority of ovules in flowers do not mature seeds despite hand pollination. The role of genetic and environmental factors governing low seed:ovule ratios in N. assoanus is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420000417
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  • 4
    Electronic Resource
    Electronic Resource
    Evolution of Microsatellite Alleles in Four Species of Mice (Genus Apodemus) (2000)
    Springer
    Journal of molecular evolution 51 (2000), S. 166-172 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002390010077
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  • 5
    Electronic Resource
    Electronic Resource
    Baer subgeometry partitions (2000)
    Springer
    Journal of geometry 67 (2000), S. 23-34 
    Details
    ISSN: 1420-8997
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract For any odd integern ≥3 and prime powerq, it is known thatPG(n−1, q2) can be partitioned into pairwise disjoint subgeometries isomorphic toPG(n−1, q) by taking point orbits under an appropriate subgroup of a Singer cycle ofPG(n−1, q2). In this paper, we construct Baer subgeometry partitions of these spaces which do not arise in the classical manner. We further illustrate some of the connections between Baer subgeometry partitions and several other areas of combinatorial interest, most notably projective sets and flagtransitive translation planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01220294
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  • 6
    Electronic Resource
    Electronic Resource
    Three-dimensional model of human TIP30, a coactivator for HIV-1 Tat-activated transcription, and CC3, a protein associated with metastasis suppression (2000)
    Springer
    Cellular and molecular life sciences 57 (2000), S. 851-858 
    Details
    ISSN: 1420-9071
    Keywords: Key words. HIV-1; Tat; metastasis; TIP30; CC3.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Human TIP30 is a cofactor that specifically enhances human immunodeficiency virus-1 (HIV-1) Tat-activated transcription. The sequence of TIP30 is identical to that of CC3, a protein associated with metastasis suppression. TIP30/CC3 is a member of the short-chain dehydrogenases/reductases (SDR) family. Of the several experimentally determined SDR structures, Escherichia coli uridine diphosphate (UDP) galactose-4 epimerase is most similar to TIP30/CC3. Because the direct sequence similarity between TIP30/CC3 and E. coli UDP galactose-4 epimerase is low, we used the transitive nature of homology and employed two Aquifex aeolicus proteins as intermediaries in the homology modeling process. Comparison of our structural model with that of known SDRs reveals that TIP30/CC3 contains several well-conserved features, including a βαβ fold at the amino terminus, which we predict binds NADP(H). TIP30/CC3 contains characteristic motifs at the catalytic site of SDRs, including a serine, tyrosine, and lysine that are important in catalyzing hydride transfer between substrate and cofactor. We also predict that a unique 20-amino acid sequence found at the amino terminus is an α-helix. Because this region contains several positively and negatively charged amino acids, it may dock TIP30/CC3 to other proteins. Our structural model points to this α-helix and the SDR-like part of TIP30/CC3 for mutagenesis experiments to elucidate its role in HIV-1 Tat-activated transcription, metastasis suppression, and other cellular functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050047
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  • 7
    Electronic Resource
    Electronic Resource
    Phosphatidylethanol stimulates calcium-dependent cytosolic phospholipase A2 activity of a macrophage cell line (RAW 264.7) (2000)
    Springer
    Journal of biomedical science 7 (2000), S. 311-316 
    Details
    ISSN: 1423-0127
    Keywords: Phosphatidylethanol ; Phosphatidic acid ; Ethanol ; Phospholipase A2, cytosolic ; Phospholipase D ; RAW 264.7 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The synthesis of inflammation mediators produced from arachidonic acid is regulated primarily by the cellular concentration of free arachidonic acid. Since intracellular arachidonic acid is almost totally present as phospholipid esters, the concentration of intracellular arachidonic acid is primarily dependent on the balance between the release of arachidonic acid from membrane phospholipids and are uptake of arachidonic acid into membrane phospholipids. Cytosolic phospholipase A2 is a calcium-dependent enzyme that catalyzes the stimulus-coupled hydrolysis of arachidonic acid from membrane phospholipids. Following exposure of macrophages to various foreign or endogenous stimulants, cytosolic phospholipase A2 is activated. Treatment with these compounds may also stimulate phospholipase D activity, and, in the presence of ethanol, phospholipase D catalyzes the synthesis of phosphatidylethanol. A cell-free system was used to evaluate the effect of phosphatidylethanol on cytosolic phospholipase A2 activity. Phosphatidylethanol (0.5 µM) added to 1-stearoyl-2-[3H]-arachidonoyl-sn-glycero-3-phosphocholine vesicles stimulated cytosolic phospholipase A2 activity. However, high concentrations (20–100 µM) of phosphatidylethanol inhibited cytosolic phospholipase A2 activity. Phosphatidic acid, the normal phospholipase D product, also stimulated cytosolic phospholipase A2 activity at 0.5 µM, but had an inhibitory effect on cytosolic phospholipase A2 activity at concentrations of 50 and 100 µM. Ethanol (20–200 mM), the precursor of phosphatidylethanol, added directly to the assay did not alter cytosolic phospholipase A2 activity. These results suggest that phosphatidylethanol alters the physical properties of the substrate, and at lower concentrations of anionic phospholipids the substrate is more susceptible to hydrolysis. However, at high concentrations, phosphatidylethanol either reverses the alterations in physical properties of the substrate or phosphatidylethanol may be competing as the substrate. Both interactions may result in lower cytosolic phospholipase A2 activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02253250
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  • 8
    Electronic Resource
    Electronic Resource
    A thousand year speleothem proxy record of North Atlantic climate from Scotland (2000)
    Springer
    Climate dynamics 16 (2000), S. 815-820 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Luminescent organic matter in stalagmites may form annual bands, allowing growth rate to be precisely determined. Stalagmite growth rate is controlled by precipitation, so annual bands can be used to derive long precipitation records. A continuously banded stalagmite from a cave in NW Scotland was used to provide a 1100 year high-resolution record of precipitation. The location of the cave means that precipitation is closely linked to the North Atlantic Oscillation, for which a record is also derived. This suggests that changes in the North Atlantic Oscillation state was an important control on European climate over the past millennium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820000077
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  • 9
    Electronic Resource
    Electronic Resource
    An Integrated Approach to Reservoir Management: The Williston Reservoir Case Study (2000)
    Springer
    Environmental management 25 (2000), S. 565-578 
    Details
    ISSN: 1432-1009
    Keywords: KEY WORDS: Reservoir; First Nations; Dust control; Native vegetation; Integrated resource management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002679910044
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  • 10
    Electronic Resource
    Electronic Resource
    Experimental investigation of large-ion-lithophile-element-, high-field-strength-element- and rare-earth-element-partitioning between calcic amphibole and basaltic melt: the effects of pressure and oxygen fugacity (2000)
    Springer
    Contributions to mineralogy and petrology 140 (2000), S. 233-250 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100000181
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