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排序方式: 共有191条查询结果,搜索用时 15 毫秒
1.
haemolysin of Escherichia coli: Comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins 总被引:3,自引:0,他引:3
Roland Benz reas Döbereiner Albrecht Ludwig Werner Goebel 《FEMS microbiology letters》1992,105(1-3):55-62
Abstract Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli . The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes. 相似文献
2.
Andrea Streit reas Faissner Bernd Gehrig Melitta Schachner 《Journal of neurochemistry》1990,55(5):1494-1506
The monoclonal L5 antibody reacts with an N-glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na2 35SO4 and a 3H-amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [35S]methionine-labeled L5 proteoglycan from cultured astrocytes with proteinase-free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores. 相似文献
3.
4.
Expression of Biologically Active Basic Fibroblast Growth Factor by Genetically Modified Rat Primary Skin Fibroblasts 总被引:1,自引:0,他引:1
Jasodhara Ray Joanna Hogg reas S. Beutler Hideichi Takayama Andrew Baird Fred H. Gage 《Journal of neurochemistry》1995,64(2):503-513
Abstract: Basic fibroblast growth factor (FGF-2) is normally expressed as a cell-associated protein, and accordingly it is not clear how it exerts its action on target cells in vivo. It has been proposed that cells release, by death or other mechanisms, small amounts of FGF-2 that then acts in an autocrine manner. To address the question of whether it is necessary that FGF-2 remain cell associated or needs to be secreted from cells to have biological activity, we expressed the 18-kDa form of FGF-2 in primary fibroblasts as a cell-associated (FGF-2-B) or as a secreted (FGF-2-S) protein. FGF-2 protein is detected in cell lysates and membrane fractions of both cell types, whereas it is present in significant amounts only in the conditioned medium of FGF-2-S cells. No FGF-2 is detected in control (untransfected) cells. FGF-2-S cells also grow faster than the control or FGF-2-B cells. Yet, when evaluated for their ability to promote the survival of embryonic hippocampal neurons in vitro, both the cell types are active, establishing the activity of the transgene product. We conclude that FGF-2 is active when engineered to be expressed as a cell-associated form or secreted from cells. 相似文献
5.
Microdistribution of butterflies in a mosaic-like habitat: The role of nectar sources 总被引:7,自引:0,他引:7
The microdistribution of five butterfly species through their flying season was analyzed in a mosaic-like habitat, brought about by secondary succession In order to explain the patterns observed, activity patterns and the use and distribution of nectar sources were determined Emphasis was laid on the changing allocation of visits to flower species and changing abundances of flowers during the season The use of nectar sources was basically limited to three flower species, Centaurea scabiosa, C bracteata and Serratula tinctoria As a consequence, niche breadth values were generally low and niche overlaps generally high Some butterflies changed their patterns of flower visits during the season and therefore reduced niche overlap with the other butterfly species The microdistribution of Melanargia galathea, Lysandra condon, Ochlodes venatus and Lictoria achilleae was strongly influenced by the distribution of their preferred nectar sources as well as by areas generally rich in flowers Changing flower preferences of Melanargia galathea and Lysandra coridon males during the course of the season were also expressed by changes in the correlations between the distribution of these butterflies and their nectar plants The distribution of nectar sources was not found to be of importance for Coenonympha arcanta, a species which rarely visited flowers 相似文献
6.
Dispersal failure contributes to plant losses in NW Europe 总被引:1,自引:0,他引:1
Wim A. Ozinga Christine Römermann Renée M. Bekker reas Prinzing Wil L. M. Tamis Joop H. J. Schaminée Stephan M. Hennekens Ken Thompson Peter Poschlod Michael Kleyer Jan P. Bakker Jan M. van Groenendael 《Ecology letters》2009,12(1):66-74
The ongoing decline of many plant species in Northwest Europe indicates that traditional conservation measures to improve the habitat quality, although useful, are not enough to halt diversity losses. Using recent databases, we show for the first time that differences between species in adaptations to various dispersal vectors, in combination with changes in the availability of these vectors, contribute significantly to explaining losses in plant diversity in Northwest Europe in the 20th century. Species with water- or fur-assisted dispersal are over-represented among declining species, while others (wind- or bird-assisted dispersal) are under-represented. Our analysis indicates that the 'colonization deficit' due to a degraded dispersal infrastructure is no less important in explaining plant diversity losses than the more commonly accepted effect of eutrophication and associated niche-based processes. Our findings call for measures that aim to restore the dispersal infrastructure across entire regions and that go beyond current conservation practices. 相似文献
7.
Johansson LC Arnlund D White TA Katona G Deponte DP Weierstall U Doak RB Shoeman RL Lomb L Malmerberg E Davidsson J Nass K Liang M Andreasson J Aquila A Bajt S Barthelmess M Barty A Bogan MJ Bostedt C Bozek JD Caleman C Coffee R Coppola N Ekeberg T Epp SW Erk B Fleckenstein H Foucar L Graafsma H Gumprecht L Hajdu J Hampton CY Hartmann R Hartmann A Hauser G Hirsemann H Holl P Hunter MS Kassemeyer S Kimmel N Kirian RA Maia FR Marchesini S Martin AV Reich C Rolles D Rudek B Rudenko A Schlichting I 《Nature methods》2012,9(3):263-265
X-ray free electron laser (X-FEL)-based serial femtosecond crystallography is an emerging method with potential to rapidly advance the challenging field of membrane protein structural biology. Here we recorded interpretable diffraction data from micrometer-sized lipidic sponge phase crystals of the Blastochloris viridis photosynthetic reaction center delivered into an X-FEL beam using a sponge phase micro-jet. 相似文献
8.
Anabaenopsis spp. are heterocytous cyanobacteria commonly found in tropical, subtropical, and temperate water bodies. So far, the knowledge
about the phylogeny of this genus is poor. Therefore, we have isolated 15 Anabaenopsis spp. strains from Kenyan and Mexican alkaline and saline water bodies and from a Ugandan freshwater body and studied the
morphology and phylogeny in a polyphasic approach. Morphologically, the investigated strains could be discriminated in two
groups. One group was containing six Anabaenopsis abijatae and A. cf. abijatae strains with up to more than 500 vegetative cells in one filament, mostly single intercalary heterocyte formation, and the
ability to branch out. The other group comprised nine strains of Anabaenopsis elenkinii with short filaments with up to 38 vegetative cells, intercalary heterocytes in pairs, and no ability to branch out. The
morphological differences were reflected in the two distinct clusters, which were found in the phylogenetic trees of 16S rDNA
and PC-IGS. While the high 16S rDNA similarity values >97.5% found between all investigated A. abijatae and A. elenkinii strains support the assignment of these two species to one single genus, the morphological differences and the low similarity
values (<87.3) found in PC-IGS sequences between the two clusters indicate two separate genera. A close morphological and
phylogenetic relationship was found for A. abijatae and Anabaenopsis (Cyanospira) rippkae. 相似文献
9.
Philipp Wagner Jörn Köhler reas Schmitz Wolfgang Böhme 《Journal of Biogeography》2008,35(8):1349-1361
Aim The Kakamega Forest, western Kenya, has been biogeographically assigned to both lowland and montane forest biomes, or has even been considered to be unique. Most frequently it has been linked with the Guineo‐Congolian rain forest block. The present paper aims to test six alternative hypotheses of the zoogeographical relationships between this forest remnant and other African forests using reptiles as a model group. Reptiles are relatively slow dispersers, compared with flying organisms (Aves and Odonata) on which former hypotheses have been based, and may thus result in a more conservative biogeographical analysis. Location Kakamega Forest, Kenya, Sub‐Saharan Africa. Methods The reptile diversity of Kakamega Forest was evaluated by field surveys and data from literature resources. Faunal comparisons of Kakamega Forest with 16 other African forests were conducted by the use of the ‘coefficient of biogeographic resemblance’ using the reptile communities as zoogeographic indicators. Parsimony Analysis of Endemism and Neighbour Joining Analysis of Endemism were used to generate relationship trees based on an occurrence matrix with paup *. Results The analysis clearly supports the hypothesis that the Kakamega Forest is the easternmost fragment of the Guineo‐Congolian rain forest belt, and thus more closely related to the forests of that Central–West African complex than to any forest further east, such as the Kenyan coastal forests. Many Kenyan reptile species occur exclusively in the Kakamega Forest and its associated forest fragments. Main conclusions The Kakamega Forest is the only remnant of the Guineo‐Congolian rain forest in the general area. We assume that the low degree of resemblance identified for the Guineo‐Congolian forest and the East African coastal forest reflect the long history of isolation of the two forest types from each other. Kenyan coastal forests may have been historically connected through forest ‘bridges’ of the southern highlands with the Congo forest belt, allowing reptile species to migrate between them. The probability of a second ‘bridge’ located in the region of southern Tanzanian inselbergs is discussed. Although not particularly rich in reptile species, the area should be considered of high national priority for conservation measures. 相似文献
10.