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  • 1995-1999  (139)
  • 1
    Electronic Resource
    Electronic Resource
    A multi-factorial experiment on heart rate variations in the intertidal crab Pachygrapsus marmoratus (1999)
    Springer
    Marine biology 135 (1999), S. 341-345 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A multi-factorial experiment was designed to investigate the effect of the following factors on the cardiac activity of the intertidal crab Pachygrapsus marmoratus: respiratory medium (air, water), temperature (four levels, 10, 17.5, 25, 32.5 °C), season (winter, summer) and body size (two levels, carapace ≤21 mm and carapace 〉21 mm). The results showed that the heart rate of P. marmoratus increased linearly with temperature and decreased when the specimens were exposed to air rather than water. Moreover, the heart rate values in summer were lower than those in winter at the corresponding temperature and body size. The summer heart rate–temperature regression line was laterally (to the right) shifted with respect to the winter line, suggesting a seasonal acclimation. Body size affected heart rate only at the acclimation temperature (17.5 °C), while no significant effect was detected at lower or higher temperatures. During the reproductive season a separate experiment was carried out to assess the effect of sex and reproductive status on heart rate. No significant difference was found among mean values of males, berried females and females without eggs. The results of the present study confirm the high physiological plasticity of this species, suggesting that P. marmoratus is a truly amphibious crab, able to deal with both water- and air-breathing during its activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050632
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  • 2
    Electronic Resource
    Electronic Resource
    Factors affecting variability of foraging excursions in a population of the limpet Patella vulgata (Mollusca, Gastropoda) (1995)
    Springer
    Marine biology 122 (1995), S. 265-270 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Paths moved by the limpet Patella vulgata L. were monitored on a sheltered vertical rocky shore in North Wales using time-lapse photography throughout nocturnal low tides in April and November 1992, roughly corresponding to periods of minimum and maximum gonad ripeness, respectively. Various motion parameters, including total duration, total length, and maximum distance reached from home were computed from 124 complete foraging routes obtained from 18 higher-zoned and 18 lower-zoned limpets. P. vulgata typically performed a single loop per night (average total length, ca. 70 cm), moving from the individual home scar to graze the surrounding algal grounds (average maximum distance, ca. 25 cm), then following its own trail back home. On the average, limpets moved from the home scar during three of four available nocturnal low tides and exploited about half the emersion time. Evidence for size-related variability in behaviour was found, as a positive correlation was assessed between both total duration and legth of the excursions, and shell length. In addition, zonation was proved to affect the limpets' foraging behaviour, since low-shore limpets moved faster and covered greater distances than high-shore ones. Moreover, consistent seasonal variation in foraging behaviour emerged, since in April the excursions were longer and longer-lasting than in November, but limpets exploited a larger fraction of potential activity phases in November than in April. The within-population variability in the temporal and spatial characteristics of the foraging excursions is discussed in relation to the available data on zonal and seasonal variation of food resources and in relation to physiological changes due to reproductive cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348939
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  • 3
    Electronic Resource
    Electronic Resource
    A versatile computer-controlled pulsed nuclear quadrupole resonance spectrometer (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4676-4681 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new, pulsed nuclear quadrupole resonance (NQR) spectrometer capable of performing a variety of pulsed and swept experiments is described. The spectrometer features phase locked, superheterodyne detection using a commercial spectrum analyzer and a fully automatic, computer-controlled tuning and matching network. The tuning and matching network employs stepper motors which turn high power air gap capacitors in a "moving grid" optimization strategy to minimize the reflected power from a directional coupler. In the duplexer circuit, digitally controlled relays are used to switch different lengths of coax cable appropriate for the different radio frequencies. A home-built pulse programmer card controls the timing of radio frequency pulses sent to the probe, while data acquisition and control software is written in Microsoft Quick Basic. Spin-echo acquisition experiments are typically used to acquire the data, although a variety of pulse sequences can be employed. Scan times range from one to several hours depending upon the step resolution and the spectral range required for each experiment. Pure NQR spectra of NaNO2 and 3-aminopyridine are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150131
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  • 4
    Electronic Resource
    Electronic Resource
    NarJ is a specific chaperone required for molybdenum cofactor assembly in nitrate reductase A of Escherichia coli (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The formation of active membrane-bound nitrate reductase A in Escherichia coli requires the presence of three subunits, NarG, NarH and NarI, as well as a fourth protein, NarJ, that is not part of the active nitrate reductase. In narJ strains, both NarG and NarH subunits are associated in an unstable and inactive NarGH complex. A significant activation of this complex was observed in vitro after adding purified NarJ-6His polypeptide to the cell supernatant of a narJ strain. Once the apo-enzyme NarGHI of a narJ mutant has become anchored to the membrane via the NarI subunit, it cannot be reactivated by NarJ in vitro. NarJ protein specifically recognizes the catalytic NarG subunit. Fluorescence, electron paramagnetic resonance (EPR) spectroscopy and molybdenum quantification based on inductively coupled plasma emission spectroscopy (ICPES) clearly indicate that, in the absence of NarJ, no molybdenum cofactor is present in the NarGH complex. We propose that NarJ is a specific chaperone that binds to NarG and may thus keep it in an appropriate competent-open conformation for the molybdenum cofactor insertion to occur, resulting in a catalytically active enzyme. Upon insertion of the molybdenum cofactor into the apo-nitrate reductase, NarJ is then dissociated from the activated enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00795.x
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  • 5
    Electronic Resource
    Electronic Resource
    Integrable dynamics of a discrete curve and the Ablowitz–Ladik hierarchy (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 1259-1273 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is shown that the following elementary geometric properties of the motion of a discrete (i.e., piecewise linear) curve select the integrable dynamics of the Ablowitz–Ladik hierarchy of evolution equations: (i) the set of points describing the discrete curve lie in the sphere S3; (ii) the distance between any two subsequent points does not vary in time; (iii) the equations of the dynamics do not depend explicitly on the radius of the sphere. These results generalize to a discrete context the previous work on continuous curves [A. Doliwa and P. M. Santini, Phys. Lett. A 185, 373 (1994)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531119
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  • 6
    Electronic Resource
    Electronic Resource
    Involvement of the narJ and mob gene products in distinct steps in the biosynthesis of the molybdoenzyme nitrate reductase in Escherichia coli (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 20 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Escherichia coli mob locus is required for synthesis of active molybdenum cofactor, molybdopterin guanine dinucleotide. The mobB gene is not essential for molybdenum cofactor biosynthesis because a deletion of both mob genes can be fully complemented by just mobA. Inactive nitrate reductase, purified from a mob strain, can be activated in vitro by incubation with protein FA (the mobA gene product), GTP, MgCl2, and a further protein fraction, factor X. Factor X activity is present in strains that lack MobB, indicating that it is not an essential component of factor X, but over-expression of MobB increases the level of factor X. MobB, therefore, can participate in nitrate reductase activation. The narJ protein is not a component of mature nitrate reductase but narJ mutants cannot express active nitrate reductase A. Extracts from narJ strains are unable to support the in vitro activation of purified mob nitrate reductase: they lack factor X activity. Although the mob gene products are necessary for the biosynthesis of all E. coli molybdoenzymes as a result of their requirement for molybdopterin guanine dinucleotide, NarJ action is specific for nitrate reductase A. The inactive nitrate reductase A derivative in a narJ strain can be activated in vitro following incubation with cell extracts containing the narJ protein. NarJ acts to activate nitrate reductase after molybdenum cofactor biosynthesis is complete.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02525.x
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  • 7
    Electronic Resource
    Electronic Resource
    Enzymatic and physiological properties of the tungsten-substituted molybdenum TMAO reductase from Escherichia coli (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 32 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The trimethylamine N-oxide (TMAO) reductase of Escherichia coli is a molybdoenzyme that catalyses the reduction of the TMAO to trimethylamine (TMA) with a redox potential of + 130 mV. We have successfully substituted the molybdenum with tungsten and obtained an active tungsto-TMAO reductase. Kinetic studies revealed that the catalytic efficiency of the tungsto-substituted TMAO reductase (W-TorA) was increased significantly (twofold), although a decrease of about 50% in its kcat was found compared with the molybdo-TMAO reductase (Mo-TorA). W-TorA is more sensitive to high pH, is less sensitive to high NaCl concentration and is more heat resistant than Mo-TorA. Most importantly, the W-TorA becomes capable of reducing sulphoxides and supports the anaerobic growth of a bacterial host on these substrates. The evolutionary implication and mechanistic significance of the tungsten substitution are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01340.x
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  • 8
    Electronic Resource
    Electronic Resource
    Potential receptor function of three homologous components, TatA, TatB and TatE, of the twin-arginine signal sequence-dependent metalloenzyme translocation pathway in Escherichia coli (1998)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 30 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.01095.x
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  • 9
    Electronic Resource
    Electronic Resource
    Cytoskeletal rearrangement in K562 erythroleukaemic cells forced to grow on a positively charged polymer surface (1999)
    Springer
    Journal of materials science 10 (1999), S. 613-620 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We have recently demonstrated that if human K562 erythroleukaemic cells, which normally grow in suspension, are grown on a positively-charged surface composed of polylysine, a transient reorganization of CD54 (ICAM-1), CD58 (LFA-3) and ανβ3 (vitronecin receptor), three important CAMs located on the cell membrane, takes place. In addition, changes of longer duration in membrane conductivity (ionic transport across the cell membrane) and membrane permittivity (static distribution of charges across the cell membrane), indicating more permanent structural as well as functional alterations in the cell membrane, were also observed [2]. Because of the close interrelationship which exists between the cell membrane, CAMs and the cytoskeleton, changes in this intracellular network as well as in the surface morphology of K562 cells grown on the positively-charged polymer, polylysine, were examined. In particular, actin and tubulin were investigated qualitatively and quantitatively by immunofluorescence microscopy and flow cytometry, respectively, while the cell surface was studied by scanning electron microscopy (SEM). The data indicate that when K562 cells are grown onto polylysine no quantitative changes occurred to the cytoskeletal elements even if these were rearranged and that the cell membrane surface is also greatly altered. These results are discussed in light of the pivotal role played by CAMs and the cell cytoskeleton in transducing environmental stimuli, in this case those provided by a positive charge, from the cell membrane to the inside of the cell. © 1999 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008983623840
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  • 10
    Electronic Resource
    Electronic Resource
    Positively charged polymer polylysine-induced cell adhesion molecule redistribution in K562 cells (1998)
    Springer
    Journal of materials science 9 (1998), S. 755-760 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We have recently demonstrated that if human K562 erythroleukemic cells, which normally grow in suspension, are grown in polylysine-coated culture flasks for 48 h, they adhere to these flasks and grow in an anchorage-dependent like manner. Important changes in both membrane conductivity (ionic transport across the cell membrane) and membrane permittivity (static distribution of charges across the cell membrane) were also observed, indicating perturbations in membrane lipids, proteins and polysaccharides. In order to better understand the changes occurring in K562 cells exposed to polylysine and because of the important role played by cell adhesion molecules (CAMs) in cell/cell and cell/substratum interactions, and in cellular adaptation to the surrounding environment, the possible redistribution of these molecules after exposure to polylysine were investigated. In particular, the CD54 (ICAM-1), CD58 (LFA-3) and αVβ3 (vitronectin receptor) molecules were investigated at different times of growth both quantitatively and qualitatively utilizing flow cytometry and immunofluorescence microscopy, respectively. The data indicate that there were no significant quantitative variations in the CAMs examined at all the times tested. In addition, no qualitative changes were observed at 48 h (as well as 24 h) of exposure. However, shorter treatment times (30 min, 1 and 2 h) did induce important CAM reorganization. The results seem to demonstrate that this cycle of CAM redistribution may, in part, be responsible for cellular adaptation to the new growth environment of K562 cells and for the variations in membrane electrical properties observed. © 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008915305681
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