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  • molecular dynamics  (3)
  • Loosdrecht lakes  (2)
  • 1990-1994  (5)
  • 1920-1924
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 191 (1990), S. 241-248 
    ISSN: 1573-5117
    Keywords: Loosdrecht lakes ; eutrophication ; Prochlorothrix hollandica ; growth kinetics of algae ; continuous cultures ; light attenuation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phytoplankton growth in the shallow, turbid Lake Loosdrecht (The Netherlands) is importantly influenced by light availability, and thus the concentrations of the various light-attenuating materials. The system is highly eutrophic and supports an algal biomass of ca. 160 mg Chl m−3. A model is proposed here which predicts algal growth in the lake as a function of the light received and subsequent attenuation in the water column by phytoplankton, tripton and background colour. The model is based on an energy balance which relates growth rate to the ‘true’ growth yield on light energy and the energy demand for cell maintenance. The coefficients for energy conversion (Y = 0.002 gDW kJ−1) and cell maintenance (µe = 0.031 day−1) were determined from steady state growth kinetics of Prochlorothrix hollandica in light-limited laboratory flow systems with the same depth as the lake and receiving summer average conditions of irradiance. Light attenuation by phytoplankton and tripton were quantified using specific attenuation coefficients: 0.011 m2 mg−1 Chl for the phytoplankton and 0.23 m2 g−1 DW for tripton. The growth studies demonstrated that Lake Loosdrecht can support a much higher algal biomass in the absence of non-algal particulate matter. The proposed model is used to predict chlorophyll a concentrations in dependence on growth rate and levels of tripton. Since approximately 75% of the sestonic dry weight in Lake Loosdrecht may be attributed to tripton, it is concluded that the algal biomass is markedly lowered by the abundance of tripton in the water column. A knowledge of the sources and fate of tripton in the lake is thus of fundamental importance in modelling phytoplankton dynamics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5117
    Keywords: Loosdrecht lakes ; eutrophication ; underwater light ; resuspension ; wind effect ; Prochlorothrix hollandica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake Loosdrecht (The Netherlands) is shallow, highly eutrophic and subject to frequent wind-induced resuspension of settled algae and detritus. The summer phytoplankton consists of filamentous prokaryotic species. Chlorophyll a levels are rather stable over the summer at a concentration of ca. 160 mg m−3; losses due to grazing and sinking are small. Epipelic chlorophyll a concentrations range from 0 to 250, but ca. 50 mg m−2 is typical. In situ rates of change of chlorophyll a in the water column were related to specific growth rates predicted by a model for light-limited growth. In the model, incident light is partitioned among algae, tripton and background colour, to determine the light available for algal growth and cell maintenance. Model coefficients were derived primarily from laboratory studies of the growth of Prochlorothrix hollandica, an abundant species in the lake in summer. Presuming constant rates of loss due to grazing and sinking, for summers 1985 and 1986 some 56% of the variation in the chlorophyll a in the lake water was explained by change in light conditions alone and 77% by light and wind-driven resuspension of epipelic chlorophyll a together. These factors had little influence on the phytoplankton biomass in 1983 and 1984; other environmental conditions, e.g. phosphorus availability, may have been important. Also, the laboratory-derived growth kinetics of P. hollandica may not have been equally suitable for modelling in the four summers.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 174-182 
    ISSN: 0887-3585
    Keywords: molecular dynamics ; docking ; computer simulation ; substrate docking ; immunoglobulin ; rational drug design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A simple method is described to perform docking of subtrates to proteins or probes to receptor molecules by a modification of molecular dynamics simulations. The method consists of a separation of the center-of-mass motion of the substrate from its internal and rotational motions, and a separate coupling to different thermal baths for both types of motion of the substrate and for the motion of the receptor. Thus the temperatures and the time constants of coupling to the baths can be arbitrarily varied for these three types of motion, allowing either a frozen or a flexible receptor and allowing control of search rate without disturbance of internal structure. In addition, an extra repulsive term between substrate and protein was applied to smooth the interaction. The method was applied to a model substrate docking onto a model surface, and to the docking of phosphocholine onto immunoglobulin McPC603, in both cases with a frozen receptor. Using transrational temperatures of the substrate in the range of 1300-1700 K and room temperature for the internal degrees of freedom of the substrate, an efficient nontrapping exploratory search (“helicopter view”) is obtained, which visits the correct binding sites. Low energy conformations can then be further investigated by separate search or by dynamic simulated annealing. In both cases the correct minima were identified. The possibility to work with flexible receptors is discussed. © 1994 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 17 (1993), S. 412-425 
    ISSN: 0887-3585
    Keywords: normal modes ; constraint dynamics ; molecular dynamics ; lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Analysis of extended molecular dynamics (MD) simulations of lysozyme in vacuo and in aqueous solution reveals that it is possible to separate the configurational space into two subspaces: (1) an “essential” subspace containing only a few degrees of freedom in which anharmonic motion occurs that comprises most of the positional fluctuations; and (2) the remaining space in which the motion has a narrow Gaussian distribution and which can be considered as “physically constrained.” If overall translation and rotation are eliminated, the two spaces can be constructed by a simple linear transformation in Cartesian coordinate space, which remains valid over several hundred picoseconds. The transformation follows from the covariance matrix of the positional deviations. The essential degrees of freedom seem to describe motions which are relevant for the function of the protein, while the physically constrained subspace merely describes irrelevant local fluctuations. The near-constraint behavior of the latter subspace allows the separation of equations of motion and promises the possibility of investigating independently the essential space and performing dynamic simulations only in this reduced space. © 1993 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 451-464 
    ISSN: 0887-3585
    Keywords: protein force field ; protein crystal ; protein hydration ; Ca2+ binding site ; molecular dynamics ; subtilisin ; computer simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this paper we present a molecular dynamics (MD) simulation of subtilisin BPN′ in a crystalline environment containing four protein molecules and solvent. Con-formational and dynamic properties of the molecules are compared with each other and with respect to the X-ray structure to test the validity of the force field. The agreement between simulated and experimental structure using the GROMOS force field is better than that obtained in the literature using other force fields for protein crystals. The overall shape of the molecule is well preserved, as is the conformation of α-helices and β-strands. Structural differences are mainly found in loop regions. Solvent networks found in the X-ray structure were reproduced by the simulation, which was unbiased with respect to the crystalline hydration structure. These networks seem to play an important role in the stability of the protein; evidence of this is found in the structure of the active site. The weak ion binding site in the X-ray structure of subtilisin BPN′ is occupied by a monovalent ion. When a calcium ion is placed in the initial structure, three peptide ligands are replaced by 5 water ligands, whereas a potassium ion retains (in part) its original ligands. Existing force fields yield a reliable method to probe local structure and short-time dynamics of proteins, providing an accuracy of about 0.1 nm. © 1992 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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