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  • 1
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    Inhibitors of the nonmevalonate pathway of isoprenoid biosynthesis as antimalarial drugs (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-09-08
    Description: A mevalonate-independent pathway of isoprenoid biosynthesis present in Plasmodium falciparum was shown to represent an effective target for chemotherapy of malaria. This pathway includes 1-deoxy-D-xylulose 5-phosphate (DOXP) as a key metabolite. The presence of two genes encoding the enzymes DOXP synthase and DOXP reductoisomerase suggests that isoprenoid biosynthesis in P. falciparum depends on the DOXP pathway. This pathway is probably located in the apicoplast. The recombinant P. falciparum DOXP reductoisomerase was inhibited by fosmidomycin and its derivative, FR-900098. Both drugs suppressed the in vitro growth of multidrug-resistant P. falciparum strains. After therapy with these drugs, mice infected with the rodent malaria parasite P. vinckei were cured.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jomaa, H -- Wiesner, J -- Sanderbrand, S -- Altincicek, B -- Weidemeyer, C -- Hintz, M -- Turbachova, I -- Eberl, M -- Zeidler, J -- Lichtenthaler, H K -- Soldati, D -- Beck, E -- New York, N.Y. -- Science. 1999 Sep 3;285(5433):1573-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Biochemistry, Academic Hospital Centre, Justus-Liebig-University, Friedrichstrasse 24, D-35392 Giessen, Germany. hassan.jomaa@biochemie.med.uni-giessen.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10477522" target="_blank"〉PubMed〈/a〉
    Keywords: Aldose-Ketose Isomerases/*antagonists & inhibitors/chemistry/genetics/metabolism ; Amino Acid Sequence ; Animals ; Antimalarials/*pharmacology ; Cloning, Molecular ; Enzyme Inhibitors/pharmacology ; Fosfomycin/*analogs & derivatives/pharmacology ; Genes, Protozoan ; *Hemiterpenes ; Malaria/*drug therapy/parasitology ; Malaria, Falciparum/drug therapy/parasitology ; Mevalonic Acid/metabolism ; Mice ; Molecular Sequence Data ; Multienzyme Complexes/*antagonists & inhibitors/chemistry/genetics/metabolism ; Organelles/drug effects/metabolism ; Organophosphorus Compounds/metabolism ; Oxidoreductases/*antagonists & inhibitors/chemistry/genetics/metabolism ; Pentosephosphates/*metabolism ; Plasmodium falciparum/*drug effects/genetics/metabolism ; Recombinant Proteins/antagonists & inhibitors/metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Terpenes/*pharmacology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Growth and alkaloid contents in leaves of Tabernaemontana pachysiphon Stapf (Apocynaceae) as influenced by light intensity, water and nutrient supply (1996)
    Springer
    Oecologia 107 (1996), S. 160-169 
    Details
    ISSN: 1432-1939
    Keywords: Monoterpene indole alkaloids ; Tropical trees ; Abiotic factors ; Growth ; C/N balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of Tabernaemontana pachysiphon (Apocynaceae) plants and the alkaloid content of leaves were investigated in the greenhouse at three levels of nutrient supply under two contrasting water and light regimes. We determined height increment, above-ground biomass production, leaf size, specific leaf weight and the content of the alkaloids apparicine, A2, isovoacangine, tubotaiwine and tubotaiwine-N-oxide. The effects of major controlling factors such as light, water and nutrient supply could be directly correlated with growth and were largely independent of each other. In contrast, leaf-alkaloid contents were influenced by interdependencies among the main factors and individually affected in a synergistic or antagonistic manner which deviated from the effects on growth. The following general trends could be identified with respect to the quantitatively predominant alkaloids apparicine, tubotaiwine and isovoacangine. Increasing nutrient supply had a positive effect on both growth and alkaloid content. Drought increased alkaloid content, but retarded growth. High light intensity lowered alkaloid content but promoted growth. We investigated the relationship between primary production and the production of secondary metabolites with respect to relative and total alkaloid content as well as in relation to the leaves' nitrogen status. Our results showed that under conditions of low nutrient supply, higher proportions of leaf nitrogen were allocated to alkaloids than at moderate or high nutrient supply. Under conditions of drought and low light, all plants allocated almost equal proportions of leaf nitrogen to alkaloids, regardless of fertiliser. Total alkaloid content per plant, however, increased with fertilisation. With respect to the N-allocation strategy, we found no indication of a trade-off between primary production and the production of secondary metabolites in this species. Rather, our results are in accordance with the carbon nutrient balance hypothesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327899
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  • 3
    Electronic Resource
    Electronic Resource
    Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.). II. Seasonal changes in the fluidity of thylakoid membranes (1998)
    Springer
    Planta 204 (1998), S. 201-206 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Electron paramagnetic resonance ; Frost hardening ; Membrane fluidity ; Photoperiod ; Scots pine ; Thylakoid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The fluidity of chloroplast thylakoid membranes of frost-tolerant and frost-sensitive needles of␣three- to four-year-old Scots pine (Pinus sylvestris L.) trees, of liposomes produced from the lipids of the thylakoids of these needles, and of liposomes containing varying amounts of light-harvesting complex (LHC) II protein was investigated by means of electron paramagnetic resonance (EPR) measurements using spin-labelled fatty acids as probes. Broadening of the EPR-resonance signals of 16-doxyl stearic acid in chloroplast membranes of frost-sensitive needles and changes in the amplitudes of the peaks were observed upon a decrease in temperature from +30 °C to −10 °C, indicating a drastic loss in rotational mobility. The lipid molecules of the thylakoid membranes of frost-tolerant needles exhibited greater mobility. Moderate frost resistance could be induced in Scots pine needles by short-day treatment (Vogg et al., 1997, Planta, this issue), and growth of the trees under short-day illumination (9 h) resulted in a higher mobility of the chloroplast membrane lipids than did growth under long-day conditions (16 h). The EPR spectrum of thylakoids from frost-tolerant needles at −10 °C was typical of a spin label in highly fluid surroundings. However, an additional peak in the low-field range appeared in the subzero temperature range for the chloroplast membranes of frost-sensitive needles, which represents spin-label molecules in a motionally restricted surrounding. The EPR spectra of thylakoids and of liposomes of thylakoid lipids from frost-hardy needles were identical at +30 °C and −10 °C. The corresponding spectra from frost-sensitive plants revealed an additional peak for the thylakoids, but not for the pure liposomes. Hence, the domains with restricted mobility could be attributed to protein-lipid interactions in the membranes. Broadening of the spectrum and the appearance of an additional peak was observed with liposomes of pure distearoyl phosphatidyl glycerol modified to contain increasing amounts of LHC II. These results are discussed with respect to a loss of chlorophyll and chlorophyll-binding proteins in thylakoids of Scots pine needles under winter conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050247
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  • 4
    Electronic Resource
    Electronic Resource
    Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function (1998)
    Springer
    Planta 204 (1998), S. 193-200 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Chlorophyll ; Chlorophyll-binding protein ; Frost hardening ; Photosynthesis ; Pinus (frost hardening)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Photosynthetic CO2 uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO2 with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050246
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis and properties of a cellulose exchanger with the crown ether diaminodibenzo-17-crown-5 as anchor group (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 227 (1995), S. 101-110 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein Cellulose- Austauscher wurde aus “o-Aminophenol-Cellulose” durch Diazotieren und Kuppeln mit Diaminodibenzo-17-krone-5 hergestellt. Die Verteilungskoeffizienten für Ca2+, Sr2+, Ba2+, Na+ und K+ wurden in Wasser/Methanol-Mischungen als Funktion des Wassergehaltes bestimmt. Die Trennung von Ca2+, Na+ und K+ und die Fraktionierung der Calciumisotope 48Ca und 40Ca wurde untersucht. Der Anreicherungsfaktor ε = 4.9 · 10-3 für 48Ca2+ ist merklich größer als der für Kationenaustauscher mit SO3H-Gruppen gefundene, aber niedriger als der in der Literatur für bestimmte Kryptanden angegebene Wert.
    Notes: A new cellulose exchanger was synthesized from “o-aminophenolcellulose” by diazotation and coupling with diaminodibenzo-17-crown-5. The distribution coefficients for Ca2+, Sr2+, Ba2+, Na+ and K+ were determined in water/methanol mixtures as a function of the water content. Separation of Ca2+, Na+ and K+ and fractionation of the calcium isotopes 48Ca and 40Ca were investigated. The enrichment factor ε = 4.9 · 10-3 for 48Ca2+ is appreciably higher than that found for cation exchange resins with —SO3H groups, but lower than that reported for certain cryptands.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052270110
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  • 6
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    The oxygen and carbon dioxide compensation points of C3 plants: possible role in regulating atmospheric oxygen. (1995)
    National Academy of Sciences
    Details
    Publication Date: 1995-11-21
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Infrared detection of aliphatic organics on a cometary nucleus (2020)
    Springer Nature
    Details
    Publication Date: 2020
    Electronic ISSN: 2397-3366
    Topics: Physics
    Published by Springer Nature
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  • 8
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    Hydrogen plasma chemical cleaning of metallic substrates and silicon wafers (1995)
    Elsevier
    Details
    Publication Date: 1995-12-01
    Print ISSN: 0257-8972
    Electronic ISSN: 1879-3347
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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  • 9
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    CO and HCN isotopologue ratios in the outflows of AGB stars (2020)
    EDP Sciences
    Details
    Publication Date: 2020-06-01
    Description: Context. Isotopologue line intensity ratios of circumstellar molecules have been widely used to trace the photospheric elemental isotopic ratios of evolved stars. However, depending on the molecular species and the physical conditions of the environment, the isotopologue ratio in the circumstellar envelope (CSE) may deviate considerably from the stellar atmospheric value. Aims. In this paper, we aim to examine how the 12CO/13CO and H12CN/H13CN abundance ratios vary radially due to chemical reactions in the outflows of asymptotic giant branch (AGB) stars and the effect of excitation and optical depth on the resulting line intensity ratios. We study both carbon-rich (C-type) and oxygen-rich (O-type) CSEs. Methods. We performed chemical modeling to derive radial abundance distributions of our selected species in the CSEs over a wide range of mass-loss rates (10−8 〈 Ṁ 〈 10−4 M⊙ yr−1). We used these as input in a non-local thermodynamic equilibrium radiative transfer code to derive the line intensities of several ground-state rotational transitions. We also test the influence of stellar parameters, physical conditions in the outflows, the intensity of the interstellar radiation field, and the importance of considering the chemical networks in our model results. Results. We quantified deviations from the atmospheric value for typical outflows. We find that the circumstellar value of 12CO/13CO can deviate from its atmospheric value by up to 25–94% and 6–60% for C- and O-type CSEs, respectively, in radial ranges that depend on the mass-loss rate. We show that variations of the intensity of the interstellar radiation field and the gas kinetic temperature can significantly influence the CO isotopologue abundance ratio in the outer CSEs of both C-type and O-type. On the contrary, the H12CN/H13CN abundance ratio is stable throughout the CSEs for all tested mass-loss rates. The radiative transfer modeling shows that the integrated line intensity ratio I12CO/I13CO of different rotational transitions varies significantly for stars with mass-loss rates in the range from 10−7 to 10−6 M⊙ yr−1 due to combined chemical and excitation effects. In contrast, the excitation conditions for the HCN isotopologues are the same for both isotopologues. Conclusions. We demonstrate the importance of using the isotopologue abundance profiles from detailed chemical models as inputs to radiative transfer models in the interpretation of isotopologue observations. Previous studies of circumstellar CO isotopologue ratios are based on multi-transition data for individual sources and it is difficult to estimate the errors in the reported values due to assumptions that are not entirely correct according to this study. If anything, previous studies may have overestimated the circumstellar 12CO/13CO abundance ratio. The use of the HCN molecule as a tracer of C isotope ratios is affected by fewer complicating problems, but we note that the corrections for high optical depths are very large in the case of high-mass-loss-rate C-type CSEs; and in O-type CSEs the H13CN lines may be too weak to detect.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 10
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    DEATHSTAR: Nearby AGB stars with the Atacama Compact Array (2020)
    EDP Sciences
    Details
    Publication Date: 2020-08-01
    Description: Context. This is the first publication from the DEATHSTAR project. The overall goal of the project is to reduce the uncertainties of the observational estimates of mass-loss rates from evolved stars on the Asymptotic Giant Branch (AGB). Aim. The aim in this first publication is to constrain the sizes of the 12CO emitting region from the circumstellar envelopes around 42 mostly southern AGB stars, of which 21 are M-type and 21 are C-type, using the Atacama Compact Array (ACA) at the Atacama Large Millimeter/submillimeter Array. The symmetry of the outflows is also investigated. Methods. Line emission from 12CO J = 2→1 and 3→2 from all of the sources were mapped using the ACA. In this initial analysis, the emission distribution was fit to a Gaussian distribution in the uv-plane. A detailed radiative transfer analysis will be presented in a future publication. The major and minor axis of the best-fit Gaussian at the line center velocity of the 12CO J = 2→1 emission gives a first indication of the size of the emitting region. Furthermore, the fitting results, such as the Gaussian major and minor axis, center position, and the goodness of fit across both lines, constrain the symmetry of the emission distribution. For a subsample of sources, the measured emission distribution is compared to predictions from previous best-fit radiative transfer modeling results. Results. We find that the CO envelope sizes are, in general, larger for C-type than for M-type AGB stars, which is as expected if the CO/H2 ratio is larger in C-type stars. Furthermore, the measurements show a relation between the measured (Gaussian) 12CO J = 2→1 size and circumstellar density that, while in broad agreement with photodissociation calculations, reveals large scatter and some systematic differences between the different stellar types. For lower mass-loss-rate irregular and semi-regular variables of both M- and C-type AGB stars, the 12CO J = 2→1 size appears to be independent of the ratio of the mass-loss rate to outflow velocity, which is a measure of circumstellar density. For the higher mass-loss-rate Mira stars, the 12CO J = 2→1 size clearly increases with circumstellar density, with larger sizes for the higher CO-abundance C-type stars. The M-type stars appear to be consistently smaller than predicted from photodissociation theory. The majority of the sources have CO envelope sizes that are consistent with a spherically symmetric, smooth outflow, at least on larger scales. For about a third of the sources, indications of strong asymmetries are detected. This is consistent with what was found in previous interferometric investigations of northern sources. Smaller scale asymmetries are found in a larger fraction of sources. Conclusions. These results for CO envelope radii and shapes can be used to constrain detailed radiative transfer modeling of the same stars so as to determine mass-loss rates that are independent of photodissociation models. For a large fraction of the sources, observations at higher spatial resolution will be necessary to deduce the nature and origin of the complex circumstellar dynamics revealed by our ACA observations.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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