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排序方式: 共有1659条查询结果,搜索用时 15 毫秒
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T. R. Shankar Raman 《Journal of biosciences》1997,22(2):203-218
Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in relation to habitat. Predictions of hypotheses relating animal density,
rainfall, habitat structure, and breeding seasonality, to changes in chital group size were assessed simultaneously using
multiple regression models of monthly data collected over a 2 yr period in Guindy National Park, in southern India. Over 2,700
detections of chital groups were made during four seasons in three habitats (forest, scrubland and grassland). In scrubland
and grassland, chital group size was positively related to animal density, which increased with rainfall. This suggests that
in these habitats, chital density increases in relation to food availability, and group sizes increase due to higher encounter
rate and fusion of groups. The density of chital in forest was inversely related to rainfall, but positively to the number
of fruiting tree species and availability of fallen litter, their forage in this habitat. There was little change in mean
group size in the forest, although chital density more than doubled during the dry season and summer. Dispersion of food items
or the closed nature of the forest may preclude formation of larger groups. At low densities, group sizes in all three habitats
were similar. Group sizes increased with chital density in scrubland and grassland, but more rapidly in the latter—leading
to a positive relationship between openness and mean group size at higher densities. It is not clear, however, that this relationship
is solely because of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard antler)
was positively related to mean group size in forest and scrubland, probably reflecting the increase in group size due to solitary
males joining with females during the rut. The fission-fusion system of group formation in chital is thus interactively influenced
by several factors. Aspects that need further study, such as interannual variability, are highlighted. 相似文献
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Adaptation to hypoxia, defined as a condition of inadequate oxygen supply, has enabled humans to successfully colonize high altitude regions. The mechanisms attempted by organisms to cope with short-term hypoxia include increased ATP production via anaerobic respiration and stabilization of Hypoxia Inducible Factor 1α (HIF-1α). However, less is known about the means through which populations adapt to chronic hypoxia during the process of development within a life time or over generations. Here we show that signaling via the highly conserved Wnt pathway impacts the ability of Drosophila melanogaster to complete its life cycle under hypoxia. We identify this pathway through analyses of genome sequencing and gene expression of a Drosophila melanogaster population adapted over >180 generations to tolerate a concentration of 3.5–4% O2 in air. We then show that genetic activation of the Wnt canonical pathway leads to increased rates of adult eclosion in low O2. Our results indicate that a previously unsuspected major developmental pathway, Wnt, plays a significant role in hypoxia tolerance. 相似文献
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Summary Amyloglucosidase (exo-1, 4- -D-glucosidase, EC 3.2.1.3), was coupled to glutaraldehyde activated Indion 48-R (a cross-linked macroporous anion exchanger) by Schiff base reaction. Immobilization brought about a marginal increase in the apparent Km. The bound enzyme exhibited increased stability towards urea and metal ions, but was less stable in the presence of guanidine hydrochloride. Immobilized amyloglucosidase could be stored at 4°C (in wet state) for 6–8 months without any apparent loss of activity. 相似文献
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S Swaminathan G Ravishanker D L Beveridge R Lavery C Etchebest H Sklenar 《Proteins》1990,8(2):179-193
A new procedure for the graphic analysis of molecular dynamics (MD) simulations on proteins is introduced, in which comprehensive visualization of results and pattern recognition is greatly facilitated. The method involves determining the conformational and helicoidal parameters for each structure entering the analysis via the method "Curves," developed for proteins by Sklenar, Etchebest, and Lavery (Proteins: Structure, Function Genet. 6:46-60, 1989) followed by a novel computer graphic display of the results. The graphic display is organized systematically using conformation wheels ("dials") for each torsional parameter and "windows" on the range values assumed by the linear and angular helicoidal parameters, and is present in a form isomorphous with the primary structure per se. The complete time evolution of dynamic structure can then be depicted in a set of four composite figures. Dynamic aspects of secondary and tertiary structure are also provided. The procedure is illustrated with an analysis of a 50 psec in vacuo simulation on the 58 residue protein, bovine pancreatic trypsin inhibitor (BPTI), in the vicinity of the local minimum on the energy surface corresponding to a high resolution crystal structure. The time evolution of 272 conformational and 788 helicoidal parameters for BPTI is analyzed. A number of interesting features can be discerned in the analysis, including the dynamic range of conformational and helicoidal motions, the dynamic extent of 2 degrees structure motifs, and the calculated fluctuations in the helix axis. This approach is expected to be useful for a critical analysis of the effects of various assumptions about force field parameters, truncation of potentials, solvation, and electrostatic effects, and can thus contribute to the development of more reliable simulation protocols for proteins. Extensions of the analysis to present differential changes in conformational and helicoidal parameters is expected to be valuable in MD studies of protein complexes with substrates, inhibitors, and effectors and in determining the nature of structural changes in protein-protein interactions. 相似文献
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The structure and internal motions of the protein hen egg white lysozyme are studied by analysis of simulation and experimental data. A molecular dynamics simulation and an energy minimization of the protein in vacuum have been made and the results compared with high-resolution structures and temperature factors of hen egg white lysozyme in two different crystal forms and of the homologous protein human lysozyme. The structures obtained from molecular dynamics and energy minimization have root-mean-square deviations for backbone atoms of 2.3 Å and 1.1–1.3 Å, respectively, relative to the crystal structures; the different crystal structures have root-mean-square deviations of 0.73–0.81 Å for the backbone atoms. In comparing the backbone dihedral angles, the difference between the dynamics and the crystal structure on which it is based is the same as that between any two crystal structures. The internal fluctuations of atomic positions calculated from the molecular dynamics trajectory agree well with the temperature factors from the three structures. Simulation and crystal results both show that there are large motions for residues involved in exposed turns of the backbone chain, relatively smaller motions for residues involved in the middle of helices or β-sheet structures, and relatively small motions of residues near disulfide bridges. Also, both the simulation and crystal data show that side-chain atoms have larger fluctuations than main-chain atoms. Moreover, the regions that have large deviations among the x-ray crystal structures, which indicates flexibility, are found to have large fluctuations in the simulation. 相似文献
10.
Freshly harvested seeds of soybean and barley were artificially aged. The progeny showed a marked decrease in mitotic index and chromosomal aberrations of various types increased at both mitosis and meiosis, resulting in a significant loss of pollen viability as the ageing advanced. Studies on the types and frequencies of chlorophyll deficients and phenodeviants also showed an overall increase, suggesting that ageing mimics irradiation effects and produces alterations in the gene complexes resulting in the segregation of different kinds of phenotypic mutations. 相似文献