Diuretic factors and second messengers stimulate secretion of the organic cation TEA by the Malpighian tubules of Drosophila melanogaster

This study showed that four factors which stimulate transepithelial fluid secretion and inorganic ion transport across the main segment of the Malpighian tubules of Drosophila melanogaster also stimulate transepithelial secretion of the prototypical organic cation tetraethylammonium (TEA). TEA fluxes across the Malpighian tubules and gut were measured using a TEA-selective self-referencing (TEA-SeR) microelectrode. TEA flux across isolated Malpighian tubules was also measured using a TEA-selective microelectrode positioned in droplets of fluid secreted by tubules set up in a modified Ramsay assay. TEA flux was stimulated by the intracellular second messengers cAMP and cGMP, which increase the lumen-positive transepithelial potential (TEP), and also by tyramine and leucokinin-I (LK-I), which decrease TEP. The largest increase was measured in response to 1 micromol l-1 LK-I which increased transepithelial TEA flux by 72%. TEA flux in the lower tubule was stimulated slightly (13%) by 1 micromol l-1 tyramine but not by any of the other factors. TEA flux across the midgut was unaffected by cAMP, cGMP or tyramine. This is the first study to demonstrate the effects of insect diuretic factors and second messengers on excretion of organic cations.     

Morphologies and conformation transition of lentinan in aqueous NaOH solution

Molecular morphologies and conformation transition of lentinan, a beta-(1-->3)-D-glucan from Lentinus edodes, were studied in aqueous NaOH solution by atomic force microscopy (AFM), viscometry, multiangle laser light scattering, and optical rotation measurements. The results revealed that lentinan exists as triple-helical chains and as single random-coil chains at NaOH concentration lower than 0.05M and higher than 0.08M, respectively. Moreover, the dramatic changes in weight-average molecular weight Mw, radius of gyration [s2](1/2), intrinsic viscosity [eta], as well as specific optical rotation at 589 nm [alpha]589 occurred in a narrow range of NaOH concentration between 0.05 and 0.08M NaOH, indicating that the helix-coil conformation transition of lentinan was carried out more easily than that of native schizophyllan and scleroglucan, and was irreversible. For the first time, we confirmed that the denatured lentinan molecule, which was dissolved in 0.15M NaOH to be disrupted into single coil chains, could be renatured as triple helical chain by dialyzing against abundant water in the regenerated cellulose tube at ambient temperature (15 degrees C). In view of the AFM image, lentinan in aqueous solution exhibited the linear, circular, and branched species of triple helix compared with native linear schizophyllan or scleroglucan.     

Inactivated enzymes as probes of the structure of arabinoxylans as observed by atomic force microscopy

The complex structures of water-soluble wheat arabinoxylans have been mapped along individual molecules, and within populations, using the visualisation of the binding of inactivated enzymes by atomic force microscopy (AFM). It was demonstrated that site-directed mutagenesis (SDM) can be used to produce inactive enzymes as structural probes. For the SDM mutants AFM has been used to compare the binding of different xylanases to arabinoxylans. Xylanase mutant E386A, derived from the Xyn11A enzyme (Neocallimastrix patriciarium), was shown to bind randomly along arabinoxylan molecules. The xylanase binding was also monitored following Aspergillus niger arabinofuranosidase pre-treatment of samples. It was demonstrated that removal of arabinose side chains significantly altered the binding pattern of the inactivated enzyme. Xylanase mutant E246A, derived from the Xyn10A enzyme (Cellvibrio japonicus), was found to show deviations from random binding to the arabinoxylan chains. It is believed that this is due to the effect of a small residual catalytic activity of the enzyme that alters the binding pattern of the probe. Control procedures were developed and assessed to establish that the interactions between the modified xylanases and the arabinoxylans were specific interactions. The experimental data demonstrates the potential for using inactivated enzymes and AFM to probe the structural heterogeneity of individual polysaccharide molecules.     

Phase separation of cholesterol from phosphatidylserine-cholesterol mixtures in the presence of the local anesthetic tetracaine

Addition of the local anesthetic tetracaine (TTC) to multilamellar dispersions of natural phosphatidylserine (PS) causes changes in the thermotropic properties of the membrane, which can be detected by differential scanning calorimetry, and in the structure of the membrane as detected by X-ray diffraction. At molar ratio [PS]/[TTC]8.5, the melting temperature of the phospholipid shifts downwards by approximately 2.5 °C. The melting endotherm is broadened; however, there is little change in the enthalpy of melting. In ternary mixtures (PS–TTC–cholesterol), the thermotropic changes are enhanced. At [PS]/[TTC]13, the onset of phase separation of cholesterol crystals from PS in the liquid crystalline state occurs at molar fraction cholesterol (X_chol)0.28, marginally smaller than that found in the absence of the anesthetic.     

Confocal and video imaging of cytoskeleton dynamics in the leech zygote

Ooplasmic segregation in the late interphase zygote of the leech Theromyzon trizonare is accomplished by reorganization of an ectoplasmic cytoskeleton formed by polar rings and meridional bands. The dynamic properties of this cytoskeleton were explored by time-lapse confocal and video microscopy. Cytoskeleton assembly was investigated in zygotes pulse-labeled with microinjected fluorophore-tagged or biotin-tagged dimeric tubulin and G-actin. Cytoskeleton disassembly was studied by comparing the linear dimensions of the cytoskeleton at different time points during late interphase. The relative distributions of F- and-G-actin were determined after microinjection of rhodamine-labeled actin and fluorescein-labeled DNase I. Results showed that labeled precursors were readily incorporated into a network of microtubules or actin filaments. Bipolar translocation of the rings and meridional bands was accompanied by the rapid assembly and disassembly of microtubules and actin filaments. Because labeled microtubules and microfilaments gradually decreased, the rate of cytoskeleton disassembly was greater than the rate of cytoskeleton assembly. Hence, ooplasmic segregation was accompanied by the rapid turnover of cytoskeletal components. Co-distribution of F- and-G-actin during mid and late interphase may favor polymer-monomer interchange. We conclude that cytoskeleton reorganization during foundation of cytoplasmic domains can be conveniently studied in the live leech zygote after microinjection of labeled precursors.     

Structural elements involved in electron-coupled proton transfer in cytochrome c oxidase

Haem-copper oxidases are the last components of the respiratory chains in aerobic organisms. These membrane-bound enzymes energetically couple the electron transfer (eT) reactions associated with reduction of dioxygen to water, to proton pumping across the membrane. Even though the mechanism of proton pumping at the molecular level still remains to be uncovered, recent progress has presented us with the structural features of the pumping machinery and detailed information about the eT and proton-transfer reactions associated with the pumping process.     

The G protein-coupled receptor rhodopsin in the native membrane

The higher-order structure of G protein-coupled receptors (GPCRs) in membranes may involve dimerization and formation of even larger oligomeric complexes. Here, we have investigated the organization of the prototypical GPCR rhodopsin in its native membrane by electron and atomic force microscopy (AFM). Disc membranes from mice were isolated and observed by AFM at room temperature. In all experimental conditions, rhodopsin forms structural dimers organized in paracrystalline arrays. A semi-empirical molecular model for the rhodopsin paracrystal is presented validating our previously reported results. Finally, we compare our model with other currently available models describing the supramolecular structure of GPCRs in the membrane.     

Spectroscopic characterization of mononuclear, binuclear, and insoluble polynuclear oxovanadium(IV)-Schiff base complexes and their oxidation catalysis

The objective was to prepare mononuclear, binuclear, and insoluble polynuclear oxovanadium(IV)-Schiff base complexes and to use them for sulfoxidation and epoxidation of organic substrates. [VO(salen)] (complex 1) with tetradentate salen(salicylideneethylenediamine) being coordinated in the equatorial plane of oxovanadium(IV), [VO(salap)] (complex 2), and [(VO)₂(sal₂-dhdabp)] (complex 3) with tridentate salap(salicylideneorthoaminophenol) and sal₂-dhdabp(salicylidene-3,3^′-dihydroxy-4,4^′-diaminobiphenyl) being bound, respectively, in the equatorial plane, of which polynuclear complexes were constituted as monomer units, were prepared and spectroscopically characterized. A sulfide and olefins were oxidized by use of complexes 1 and 2 (mononuclear), complex 3 (binuclear), and the polynuclear complexes (poly-1 and poly-3) synthesized with 1 and 3, respectively. The reaction rates for poly-1 and -3 were a little lower than those of the corresponding 1 and 3. On oxidation of sulfides, poly-3 exhibited lowering of activity by about 15% in three cycles, while poly-1 showed significant lose of activity with each use. Poly-3 was efficient for the oxidation of the olefins only in the first cycle. It was suggested that the loss of activity depends not only on the coordination geometry of the oxovanadium complex, but also on the kind of the substrate.     

Habitat use of nightjar (Caprimulgus europaeus) in an Austrian pine forest

The Steinfeld in Lower Austria supports a population of European Nightjar (Caprimulgus europaeus) which was extensively studied during 1997 and 1998. The study area encompassed a pine forest of 20 km². The population densities of 1.05 and 1.25 territories/km², respectively, lies within the range found in central European populations. Annual monitoring until 2001 has shown the population to be stable. To gain an insight into habitat use of the species, various habitat-related parameters were measured inside and outside the territories, namely structure of trees, density of trees, structure of undergrowth vegetation and structure of clearings. Discriminant analysis was applied to assess the factors responsible for habitat choice of the Nightjar population. The findings showed that the Nightjars territories were frequently centered on a large clearing with an area of at least 0.7 ha. Clearings less than 50 m wide were not colonized. The requirement for a minimum width of a clearing in addition to a minimum area probably relates to better hunting conditions. Nightjars prefer trees where the lower edge of the crown is on average 4.38 m higher than at control points so that males can churr from dead branches immediately below the canopy. Such trees were found on the edge of clearings in the forest, and the edge of a clearing thus had a pronounced effect on the quality of a territory. In contrast to reports in the literature, neither the proportion of bare patches of ground nor the average height of undergrowth vegetation was found to be decisive for territory selection.     

Charles Darwin’s bird collection and ornithological knowledge during the voyage of H.M.S. “Beagle”, 1831–1836

This paper analyses Charles Darwins bird collection and the ornithological knowledge he derived from it during the voyage of H.M.S. Beagle. Darwin collected 468 bird skins, 10 detached parts of the lesser rhea, and the nests and eggs of 16 different taxa as well as 14 whole birds and 4 parts of birds which he preserved in spirit. He labelled these specimens with a number tag only, cross-referring the number to a notebook entry. Partly because of his limited ornithological knowledge and partly because he was confronted at times with entirely unknown birds, Darwin was often unable to apply the correct generic designations and gave his South American specimens English and Spanish names from literature and the local tongues, as well as the scientific generic names of European birds. Back home, it was John Gould, the prominent ornithologist of the Zoological Society of London, who made sense of Darwins collection, among his many other scientific achievements correctly identifying the Galápagos finches as a group of closely related birds. Darwins bird collection did not receive much attention in the latter part of the 19th century. Most of the specimens had their original labels removed and replaced by ones of the custodian institution. Today, original Darwin specimens stemming from the Beagle voyage are to be found in at least eight different institutions, but almost half of the bird specimens Darwin collected on the Beagle voyage are not accounted for. The appendix to this paper lists for the first time all the birds which Darwin collected during the voyage. Darwins famous book On the origin of species hardly draws upon any ornithological examples from his voyage on the Beagle. Nevertheless, Darwin contributed much to ornithology. His collection contained 39 new species and subspecies of birds, mainly described by Gould, and some birds from populations now extinct, and he also made a few very good field observations, published in the sections of The Zoology of the Voyage of H.M.S. Beagle dedicated to birds.