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1.
Biogeographical change in the tiger, Panthera tigris 总被引:2,自引:0,他引:2
2.
Inhibition of dehydration-induced fusion between liposomal membranes by carbohydrates as measured by fluorescence energy transfer 总被引:7,自引:1,他引:6
The relative abilities of a number of naturally occurring carbohydrates to inhibit dehydration-induced fusion between palmitoyloleoylphosphatidylcholine:phosphatidylserine (85:15) large unilamellar vesicles have been studied. Fusion events were quantified using a fluorescence resonance energy transfer technique. Trehalose was most effective at inhibiting fusion (0.4 g/trehalose/g lipid showed 30% probe intermixing), followed by maltose (60% intermixing), fructose (60%), sucrose (70%), glucose (80%), cellobiose, glycerol, raffinose, and myo-inositol (90%). The relative abilities of these carbohydrates to inhibit fusion correlate directly with their abilities to interact with phospholipids, maintain bilayer fluidity, and preserve biological membranes. The results are discussed in relation to the crystalline structure of the carbohydrates and their possible influence on level of interaction with phosphate head groups. 相似文献
3.
Single unit recordings have been made from the muscle spindles of the extensor digitorum brevis I muscle of the chelonian emys orbicularis. The responses to ramp-type mechanical stretches (up to 5 mm s?1 velocity and up to 1.6 mm extension) were compared to those of spindles from other groups. It is found that the spindles have lower rates of firing than those from the other groups with the exception of the snake spindles. Generally the spindles behaved like the secondary ending of mammalian spindles or the tonic type of snake spindle in terms of their response to the velocity of stretch. The results are consistent with the view that the tonic response arises from intrafusal muscle fibres in which the sensory region has a structure which is fairly uniform and similar to that of the polar regions and not interrupted by accumulations of nuclei. 相似文献
4.
Effects of urbanization on streams of the Melbourne region, Victoria, Australia. I. Benthic macroinvertebrate communities 总被引:11,自引:0,他引:11
Christopher J. Walsh rew K. Sharpe Peter F. Breen & Jason A. Sonneman 《Freshwater Biology》2001,46(4):535-551
1. Macroinvertebrate community composition was assessed in small streams of the Melbourne region to test the effects of (a) urban density (catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).
2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high-EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.
3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.
4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams. 相似文献
2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high-EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.
3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.
4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams. 相似文献
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In studies that employ matched pair analysis to identify environmental exposures important for a disorder, criteria for discordant pairs are seldom discussed. Yet several assumptions concerning the definition of discordancy may have considerable influence over what results are found. Problems are exacerbated when age of onset for a disorder is late in life. We propose a new set of criteria for defining discordant pairs in studies of dementia, taking into account duration of discordance and competing causes of mortality, and evaluate the consequences of choosing alternative definitions of discordancy. 相似文献
8.
The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras 总被引:1,自引:0,他引:1
Jeannie S. Wallace Allan J. Hayle Allan J. Syms Margaret Cairney Ben Tutty rew Gazzard Mark F. Evans Kenneth A. Fleming David Tarin 《Differentiation; research in biological diversity》1989,41(3):208-215
Transfection of cells with cloned genes or total genomic DNA offers a means for studying aspects of neoplastic behaviour. We have used this method to examine whether incorporation of the cloned 6.6-kilobase (kb) fragment of DNA containing the mutant c-Ha-ras human oncogene can confer metastatic capability on murine NIH 3T3 cells. Cells co-transfected with the mutated ras gene and the neomycin resistance marker pSV2neo were selected by culture in neomycin. On subcutaneous inoculation into MF 1 nude mice, these cells proved to be tumourigenic with short latent periods (approximately 14 days)--nude mice were used to circumvent immunological rejection of the mouse cells expressing the product of the human oncogene. Transfectants were capable of lung colonisation after intravenous injection, but there was no evidence of spontaneous metastasis at autopsy, or on histological examination of the lungs and other organs, 90 days after inoculation. Incorporation of the transfected oncogene was confirmed by Southern blotting and its expression by dot-blot hybridisation and immunoprecipitation. The results in this experimental system indicate that transfection of a mutated human ras oncogene into non-neoplastic 3T3 cells can confer part of the metastatic phenotype, namely lung colonisation, but is not by itself sufficient to induce spontaneous metastatic behaviour. 相似文献
9.
Proton and sucrose transport in isolated tonoplast vesicles from sugarcane stalk tissue 总被引:1,自引:0,他引:1
Tonoplast vesicles prepared from immature sugarcane ( Saccharum spp., hybrid cv. H65–7052) tissue and purified on a discontinuous dextran gradient take up sucrose. Uptake was stimulated by MgATP. Evidence that the mechanism is linked to proton transport is derived from "pH jump'data and from inhibition of ATP-stimulated sucrose transport by the protonophore carbonyl cyanide m -chlorophenylhydrazone (CCCP) and by the proton-channel blocker of proton-linked ATPases. N. N '-dicyclo-hexylcarbodiimide (DCCD). A saturable phase of sucrose uptake was found at low substrate concentrations, and a linear phase characterized uptake at higher concentrations. Uptake was specific for sucrose, as demonstrated by competition experiments with various sugars. Sucrose uptake by the vesicle fraction was inhibited by KNO3 , protonophores and protein modifying reagents, whereas sodium orthovanadate had no effect. Overall, the evidence suggests an ATP-hydrolysis-dependent tonoplasl antiport for sucrose transport, although a more direct influence of ATP on conformational changes in relevant tonoplast proteins cannot be ruled out. 相似文献
10.
Ann E. Wakefield Sarah E. Peters Suneale Banerji Paul D. Bridge Geoffrey S. Hall David L. Hawksworth Lynden A. Guiver rew G. Allen Julian M. Hopkin 《Molecular microbiology》1992,6(14):1903-1911
Pneumocystis carinii causes life-threatening pneumonia in T-lymphocyte-immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies show P. carinii to be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogen P. carinii is closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne spores. 相似文献