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  • 1
    ISSN: 1615-6102
    Keywords: Bacteroids ; Mitochondria ; Respiration ; Root nodules ; Soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A method for the separation and purification of bacteroids and mitochondria from nodules of soybean roots is described. Cross contamination between these two oxidative fractions was easily assessible by using NADH oxidase and β-hydroxybutyrate dehydrogenase respectively as specific mitochondrial and bacteroid markers. Bacteroid respiration was characterized by substantial endogenous respiration which could be reduced by keeping plants in the dark prior to isolation, and stimulated by uncoupler or organic acids. Nodule mitochondria readily oxidized external NADH and a range of tricarboxylic acid cycle intermediates, with good respiratory control. A major difference between nodule and root mitochondria was the former's high sensitivity to the inhibitors rotenone and cyanide. This indicates a reduced capacity for non-phosphorylating electron transport in nodule mitochondria, which may be related to the large energy demand during ammonia assimilation in nodule cells.
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  • 2
    ISSN: 1615-6102
    Keywords: Salticid spiders ; Principal retinae ; Receptor tiering ; Receptor mosaics ; Telephoto optics ; Visual acuity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Retinal mosaics of the four tiers of receptors (layers I–IV) in the principal eyes of two species of salticid spider known to exhibit high visual acuity are described at the ultrastructural level. The four tiers of receptors have been previously classified byLand (1969 a) andBlest et al. (1981). Only the tier (layer I) farthest from the dioptric system has a mosaic quality capable of sustaining the visual discriminations that have been demonstrated by behavioural experiments. More distal layers are of poor to negligible mosaic organization. It is shown that rhabdoms of layer I are disposed with respect to their surrounds in such a way as to enable them to act as light-guides: the ultrastructure of layer I receptors appears to be designed to minimize optical cross-talk between receptors. The cytoplasm of the more distal layers is packed with mitochondria which have been shown to equilibrate the refractive indices of the rhabdoms and the material that surrounds them. It is argued that the mitochondria show no evidence of metabolic activity, and that an optical role may be their only one. Their effect will be to minimize the degradation of images received by layer I.
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  • 3
    ISSN: 1573-4846
    Keywords: Molecular Dynamics ; Density Functional Theory ; sol-gel solutions ; silica clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Density Functional Theory is used to study water, methanol, ethanol, TMOS, and TEOS molecules and the most important silica clusters participating in sol-gel processes. Calculated bond lengths, bond angles and electric dipole moments compare well with experimental data. The energy of these molecules is reported and used to discuss the energetics of the hydrolysis and condensation reactions. Molecular Dynamics is employed to simulate liquid water, methanol, ethanol, TMOS, TEOS and experimental sol-gel solutions. Calculated densities and enthalpies of vaporisation compare well with experimental data. Preliminary results are presented for MD simulations of sol-gel solutions.
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  • 4
    ISSN: 1573-1561
    Keywords: Attractants ; human ; mosquito ; collection ; concentration ; Aedes aegypti ; Anopheles quadrimaculatus ; Diptera ; Culicidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The residue left on glass surfaces by human hands was found to be attractive to femaleAedes aegypti (L.) andAnopheles quadrimaculatus Say mosquitoes. The material lost half of its activity in 1 hr. A solvent wash technique was developed to recover and concentrate the residuum from handled glass beads. The residuum could be recovered effectively with absolute ethanol and less effectively with several other solvents. More mosquitoes were attracted to heated than to unheated residuum, an indication of its volatility. Also, attraction of the residuum decreased with decreasing concentration or dose. Concentrated residuum collections, stored under refrigeration and tested for longevity, showed no appreciable loss of attractiveness up to 60 days of storage.
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  • 5
    ISSN: 1615-6102
    Keywords: ATPase cytochemistry ; Chara corallina ; Plasmalemma ; Proton efflux ; Plasmalemmasome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytochemical adenosine triphosphatase (ATPase) activity is localised on the plasmalemma and in the tubules of plasmalemmasomes (PLSs) of cells ofChara corallina. Results obtained with centrifuged cells, with only the plasmalemma remaining, tend to confirm that this membrane is the major source of ATPase activity. X-ray microanalysis indicates that ATPase reaction deposits are most likely lead phosphate. ATPase activity is also evident on the chloroplast envelope, the mitochondrial outer membrane, the tonoplast and associated vesicles and commonly throughout the cytoplasm. Results are discussed in relation to the possibilities that the plasmalemma ATPase is a proton pumping ATPase and that the PLS may play a role in enhanced proton efflux.
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  • 6
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Transmission electron microscopy revealed that optically homogenous pleonastes occurring in titanomagnetites had been oxidised. The pleonastes had decomposed by a discontinuous mechanism to give an intergrowth of a spinel and an intermediate phase, whose structure was based on a spinel superlattice. The intermediate phase was similar to one previously found in oxidised chromites from Rhum.
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  • 7
    ISSN: 1432-2021
    Keywords: Key words Forsterite ; Atomistic simulation ; Adsorption of water ; Surface reactivity ; Morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  We describe the application of atomistic simulation techniques to investigate the effect of associative and dissociative adsorption of water on the structures and stabilities of the low-index surfaces of forsterite. All surfaces are amenable to associative adsorption of water, while dissociative adsorption is energetically favourable on all but the non-dipolar {1 0 0} surface. Often, otherwise unstable (dipolar) surfaces are stabilised to a large extent by hydration, e.g. the dipolar {0 1 0} surface. However, on thermodynamic grounds we do not expect associatively adsorbed water to dissociate on all surfaces, as the energies released for dissociative adsorption of water on the non-dipolar {0 1 0} and {1 0 0} surfaces are less than those released for associative adsorption. As such, there is no energetic incentive for the associatively adsorbed water molecules to dissociate. The stabilities of the two terminations of the {0 1 0} surface, the main cleavage plane of forsterite, are reversed when hydroxylated, indicating that some dissolution of the magnesium ions may occur upon hydration, which is shown to be an exothermic process for both surface terminations. The equilibrium morphology was calculated as a way of assessing the change in surface energies. The experimental morphology of forsterite is adequately reproduced, suggesting that the relative stabilities of the surfaces, both unhydrated and hydroxylated, are calculated correctly.
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  • 8
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract We have used a newly developed ab initio constant-pressure molecular dynamics with variable cell shape technique to investigate the zero temperature behaviour of high pressure clinoenstatite (MgSiO3-C2/c) from 0 up to 30 GPa. The optimum structure at 8 GPa, as well as structural trends under pressure, compare very well with experimental data. At this pressure, we find noticeable “fluctuations” in the chain configuration which suggests the structure is on the verge of a mechanical instability. Two distinct compressive behaviours then appear: one below and another above 8 GPa. This phenomenon may be related to the observed transition to a lower symmetry P21/c phase which involves a reconfiguration of the silicate chains, and suggests that the C2/c structure at low pressures found here, may be an artifact of the dynamical algorithm which preserves space group in the absence of symmetry breaking fluctuations. Comparison with calculations in other magnesium silicate phases, indicates that the size and shape of the silicate units (isolated and/or linked tetrahedra and octahedra) are generally well described by the local density approximation; however, the weaker linkages provided by the O-Mg-O bonds, are not as well described. This trend suggests that, as in the recently studied case of H2O-ice, the structural properties of more inhomogeneous systems, like enstatite, may be improved by using gradientcorrected density functionals.
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  • 9
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The structure and electronic properties of trigonal and orthorhombic boric oxide (B2O3) are studied using periodic ab initio Hartree-Fock method. The optimised structural parameters for two B2O3 polymorphs are in good agreement with experimental data. The analyses of their electronic structures provide insights into the chemical nature of the B–O bond and the way in which it changes with the coordination number around boron and oxygen. Our quantum-chemical study suggests that the orthorhombic form is more ionic than the trigonal form and that the coordination number of boron around oxygen plays a more dominant role than that of oxygen around boron in B2O3 crystals.
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  • 10
    ISSN: 1432-0878
    Keywords: Photoreceptor membrane turnover ; Acid phosphatases ; Autophagy ; GERL ; Nocturnal spider, Dinopis subrufus L. Koch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ultrastructural localisation of acid phosphatases (AcPhs) during the normal daily breakdown of rhabdomere membrane in Dinopis has been examined using β-glycerophosphate and p-nitrophenyl phosphate as substrates. Results are related to the classification of organelles in the receptors given by Blest, Powell and Kao (1978). Weak and infrequent reactions are obtained in multivesicular bodies (mvbs) and multilamellar bodies (mlbs) derived from them. Residual bodies (rbs) begin to react strongly as they lyse. Source of AcPhs is endoplasmic reticulum which has barely differentiated towards the GERL configuration; it becomes reactive as it is incorporated into secondary lysosomes. GERL tubules, Y-bodies and vesicles respond erratically and weakly, and are also incorporated into rbs. No evidence was found for a significant participation of Golgi bodies in these processes, and acid phosphatase cytochemistry fails to reveal a topographical relationship between GERL in these cells and Golgi saccules. Coated vesicle clusters found in the predawn receptive segments are AcPh-negative; this implies that their previous identification as GERL-derived “Nebenkerne” carrying hydrolytic enzymes to newly-formed mvbs (Blest, Kao and Powell, 1978) is dubious. Isolation bodies and autophagic vacuoles enclosing other organelles in pathological receptors give strong reactions while adjacent secondary lysosomes derived from rhabdomere membrane and associated GERL give weak ones. It is concluded that rhabdomere-derived rb lysis is more tightly regulated than other autophagic processes, and it is suggested that a high degree of control is necessary in a receptor which may repeat the autophagy of a large mass of transductive membrane at least 60–100 times in the course of its working life.
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