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  • phosphorus  (5)
  • bioactive conformation  (2)
  • 32P  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Seasonal dynamics of a cyanobacteria-dominated microbial community in surface sediments of a shallow, eutrophic lake (1989)
    Springer
    Aquatic sciences 51 (1989), S. 153-178 
    Details
    ISSN: 1420-9055
    Keywords: sediments ; cyanobacteria ; Microcystis ; bacterial biomass ; bacterial production ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The seasonal variation of microbial biomass and activity in the surface sediments (0–10 cm) of the shallow, eutrophic Lake Vallentunasjön was followed during one year. “Overwintering”Microcystis colonies dominated the microbial community during all seasons, constituting 60–90% of the total microbial biomass. Expressed on an areal basis, the benthic biomass was, throughout the year, larger than or similar to the planktonic biomass during the peak of the summer bloom, indicating an ability of the colonies to survive in the sediments for extended periods. Abundance of “other”, non-photosynthetic bacteria varied in the range 3.0–15.5 · 1010 cells g−1 d. w. over the year with minimum values in summer and maximum values in autumn in connection with the sedimentation of theMicrocystis bloom. A substantial part of the non-photosynthetic bacteria, up to circa 40%, was associated with the mucilage of healthyMicrocystis colonies. Bacterial production (3H-thymidine incorporation) appeared to be strongly temperature dependent and less influenced by the seasonal sedimentation pattern. Our data indicate an increasing proportion of non-growing cells in autumn and winter. Biomass-bound phosphorus constituted a significant portion, circa 10%, of the phosphorus content in Lake Vallentunasjön sediments. This pool has normally been overlooked in studies on phosphorus dynamics in lake sediments. Different mechanisms whereby organic phosphorus can be released from the sediments are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879300
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  • 2
    Electronic Resource
    Electronic Resource
    A pharmacophore model for dopamine D4 receptor antagonists (2000)
    Springer
    Journal of computer aided molecular design 14 (2000), S. 769-786 
    Details
    ISSN: 1573-4951
    Keywords: bioactive conformation ; conformational analysis ; dopamine D2 ; dopamine D4 ; D2/D4 selectivity ; enantioselectivity ; pharmacophore model ; solvation energies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A pharmacophore model for dopamine D4 antagonists has been developed on the basis of a previously reported dopamine D2 model. By using exhaustive conformational analyses (MM3* force field and the GB/SA hydration model) and least-squares molecular superimposition studies, a set of eighteen structurally diverse high affinity D4 antagonists have successfully been accommodated in the D4 pharmacophore model. Enantioselectivities may be rationalized by conformational energies required for the enantiomers to adopt their proposed bioactive conformations. The pharmacophore models for antagonists at the D4 and D2 receptor subtypes have been compared in order to get insight into molecular properties of importance for D2/D4 receptor selectivity. It is concluded that the bioactive conformations of antagonists at the two receptor subtypes are essentially identical. Receptor essential volumes previously identified for the D2 receptor are shown to be present also in the D4 receptor. In addition, a novel receptor essential volume in the D4 receptor, not present in the D2 receptor, has been identified. This feature may be exploited for the design of D4 selective antagonists. However, it is concluded that the major determinant for D2/D4 selectivity is the nature of the interactions between the receptor and aromatic ring systems. The effects of the electronic properties of these ring systems on the affinities for the two receptor subtypes differ substantially.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008198026843
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational energy penalties of protein-bound ligands (1998)
    Springer
    Journal of computer aided molecular design 12 (1998), S. 383-383 
    Details
    ISSN: 1573-4951
    Keywords: AMBER ; bioactive conformation ; conformational analysis ; GB/SA hydration model ; ligand–protein interactions ; MM3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformational energies required for ligands to adopt their bioactive conformations were calculated for 33 ligand–protein complexes including 28 different ligands. In order to monitor the force field dependence of the results, two force fields, MM3 and AMBER, were employed for the calculations. Conformational analyses were performed in vacuo and in aqueous solution by using the generalized Born/solvent accessible surface (GB/SA) solvation model. The protein-bound conformations were relaxed by using flat-bottomed Cartesian constraints. For about 70% of the ligand–protein complexes studied, the conformational energies of the bioactive conformations were calculated to be ≤3 kcal/mol. It is demonstrated that the aqueous conformational ensemble for the unbound ligand must be used as a reference state in this type of calculations. The calculations for the ligand–protein complexes with conformational energy penalties of the ligand calculated to be larger than 3 kcal/mol suffer from uncertainties in the interpretation of the experimental data or limitations of the computational methods. For example, in the case of long-chain flexible ligands (e.g. fatty acids), it is demonstrated that several conformations may be found which are very similar to the conformation determined by X-ray crystallography and which display significantly lower conformational energy penalties for binding than obtained by using the experimental conformation. For strongly polar molecules, e.g. amino acids, the results indicate that further developments of the force fields and of the dielectric continuum solvation model are required for reliable calculations on the conformational properties of this type of compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008007507641
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  • 4
    Electronic Resource
    Electronic Resource
    Phosphorus in sediments — speciation and analysis (1988)
    Springer
    Hydrobiologia 170 (1988), S. 91-101 
    Details
    ISSN: 1573-5117
    Keywords: phosphorus ; sediments ; fractionation ; forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Characterization of sediment phosphorus is commonly based on sequential chemical extractions, in which phosphorus is supposed to be selectively removed from different compounds in the sediments. The first extraction schemes were designed to quantify discrete chemical or mineralogical compounds. As extraction schemes have been tested on different sediments, several systematic errors have been detected and the schemes have been modified and simplified accordingly. Other chemical extractions or treatments have attempted to determine phosphorus bound to particles with a certain strength or binding energy, the purpose being to determine the labile, loosely bound, exchangeable, mobile or algal-available fraction of sediment phosphorus. All extraction procedures yield operationally defined fractions and cannot be used for identification of discrete phosphorus compounds. The many methodological modifications make it necessary to be cautious when comparing results from the literature in this field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024900
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  • 5
    Electronic Resource
    Electronic Resource
    Bioavailability of different phosphorus forms in freshwater systems (1988)
    Springer
    Hydrobiologia 170 (1988), S. 133-155 
    Details
    ISSN: 1573-5117
    Keywords: bioavailability ; phosphorus ; dissolved ; particulate ; bioassay ; 32P
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The recent literature on the bioavailability of different forms of P in freshwater systems is reviewed. Bioavailable P is defined as the sum of immediately available P and the P that can be transformed into an available form by naturally occurring processes. Methods used to estimate the bioavailable P pool, which vary between studies largely depending on the time perspective applied, are critically evaluated. Most studies on particulate P aim to determine the potentially available P pool. Potential bioavailability of particulate P is normally analysed in bioassays with algal yield determinations and the available P fraction is characterized from interpretations of results of sequential chemical extractions. NaOH-extractable P is in most studies the most algal-available P fraction. For soil samples and tributary water particulate matter, NaOH-P has often been found to be equal to algal extractable P. In other studies depletions of NaOH-P have accounted for the algal P uptake, but only a minor proportion of the fraction has been utilized. Organic P in lake water particulate matter and bed sediments of eutrophic lakes can also be algal-available to a significant extent. Studies on the bioavailability of dissolved P have often been concerned with immediate availability, or the minimum amount of available P. Such studies need other types of experimental design and normally assays with radiotracers are used. Immediately available P is frequently found to be less than P chemically assessed as dissolved reactive P (DRP) at low (〈 10 µg DRP·l-1) concentrations. However, immediate availability may also approach or exceed DRP concentrations, especially at higher concentrations. Potential bioavailability, assayed as for particulate P, may generally render higher bioavailability than P assayed as immediately available. Large fractions of dissolved P remain unutilized and are primarily found in the high molecular weight fraction of dissolved P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024902
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  • 6
    Electronic Resource
    Electronic Resource
    Exchange of phosphorus across the sediment-water interface (1988)
    Springer
    Hydrobiologia 170 (1988), S. 229-244 
    Details
    ISSN: 1573-5117
    Keywords: phosphorus ; sediments ; retention ; release ; microbial processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO3 precipitation to phosphorus retention in calcareous lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024907
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Coupling between benthic biomass of Microcystis and phosphorus release from the sediments of a highly eutrophic lake (1992)
    Springer
    Hydrobiologia 235-236 (1992), S. 375-385 
    Details
    ISSN: 1573-5117
    Keywords: Microcystis ; microbial activity ; sediment ; phosphorus ; internal loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Variations in microbial biomass and activity in the sediments of hypereutrophic Lake Vallentunasjön were followed during a period of 5 years. The data were compared to the calculated release of phosphorus from the sediments during the same period. A strong co-variation was found between biomass of Microcystis, heterotrophic bacterial activity in the sediments and internal phosphorus loading. These parameters exhibited mainly a declining trend during the investigation period. A pronounced stability of the sediment chemistry, including the fractional composition of the sediment phosphorus, during the studied period indicates that microbial activity affected the phosphorus release from the sediments. Calculations of the percentage of sediment bacteria that was associated to the mucilage of Microcystis colonies imply, together with the specific bacterial production, that Microcystis in the sediment stimulates bacterial production. In the highly phosphorus-saturated sediments of Lake Vallentunasjön this would ultimately lead to an increased release of phosphorus from the sediment. Lake Vallentunasjön does not follow the common pattern of recovery after reduction of external phosphorus loading. The large biomasses and long survival of Microcystis in the sediment are probably important reasons for the delayed recovery of the lake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026227
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