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排序方式: 共有112条查询结果,搜索用时 31 毫秒
1.
Free and polymerized tubulin in cultured bone cells and Chinese hamster ovary cells: the influence of cold and hormones 总被引:1,自引:1,他引:0
A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to- cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron- transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer. 相似文献
2.
A potentially important source of cholesterol secreted in bile is cholesterol-rich lipoproteins. However, the fate of the cholesterol carried in these lipoproteins after hepatic uptake has not been investigated. We harvested an apoE- and cholesterol-rich lipoprotein fraction (d 1.02-1.06 g/ml) from hypercholesterolemic rats and examined the acute effects of these lipoproteins on hepatic cholesterol metabolism, very low density lipoprotein (VLDL) secretion, and biliary lipid secretion. Administration of a lipoprotein bolus (20 mg of cholesterol) to rats resulted in a significant decrease in 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and a significant increase in acyl-coenzyme A:cholesterol acyltransferase activity over controls at 1 hr. Hepatic cholesteryl ester content increased 400% with no change in hepatic free cholesterol content or biliary cholesterol secretion. These cholesterol-rich lipoproteins delivered in the isolated perfused liver effected a fivefold increase in hepatic VLDL secretion with no change in composition. Therefore, cholesterol-rich lipoproteins do not acutely alter biliary cholesterol secretion. Rather, the majority of the cholesterol delivered to the liver in these lipoproteins is either esterified and stored as cholesteryl ester or resecreted as free and esterified cholesterol in hepatic VLDL. 相似文献
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The Mu Transposable Elements of Maize: Evidence for Transposition and Copy Number Regulation during Development 总被引:14,自引:8,他引:6 下载免费PDF全文
The Mu transposon of maize exists in a highly mutagenic strain called Robertson's Mutator. Plants of this strain contain 10-50 copies of the Mu element, whereas most maize strains and other plants have none. When Mutator plants are crossed to plants of the inbred line 1S2P, which does not have copies of Mu, the progeny plants have approximately the same number of Mu sequences as did their Mutator parent. Approximately one-half of these copies have segregated from their parent and one-half have arisen by transposition and are integrated into new positions in the genome. This maintenance of copy number can be accounted for by an extremely high rate of transposition of the Mu elements (10-15 transpositions per gamete per generation). When Mutator plants are self-pollinated, the progeny double their Mu copy number in the first generation, but maintain a constant number of Mu sequences with subsequent self-pollinations. Transposition of Mu and the events that lead to copy number maintenance occur very late in the development of the germ cells but before fertilization. A larger version of the Mu element transposes but is not necessary for transposition of the Mu sequences. The progeny of crosses with a Mutator plant occasionally lack Mutator activity; these strains retain copies of the Mu element, but these elements no longer transpose. 相似文献
5.
Variants of a cloned laboratory stock of the trypanosomatid parasite Crithidia luciliae have been distinguished from "parental type" organisms. These variants accumulated spontaneously over time as the protozoan was maintained by continuous passage in a chemically defined medium. Cloned lines of these variants have been isolated by plating on nutrient agar and partially characterized on the basis of their growth characteristics in culture, their colony and cellular morphology as well as their surface protein expression. One cloned line consisted of motile, flagellated forms which, unlike "parental type" organisms, did not adhere to the surface of culture flasks. Another cloned line was composed of non-adherent, nonmotile, amastigote-like forms which were further distinguished from "parental type" cells by virtue of their constitutive expression, in nutrient-replete medium, of high levels of a surface membrane associated 3'-nucleotidase/nuclease (3'-N'ase) activity. Both the motile, flagellated and amastigote-like variants, like the "parental type" organisms, exhibited elevated levels of the 3'-N'ase activity upon exposure to purine starvation conditions. The variants described are of potential importance in elucidating the mechanism of induction of the highly regulated 3'-N'ase activity as well as for understanding the cytoskeletal systems and the surface properties of these protozoa. 相似文献
6.
Movements and associations of ribosomal subunits in a secretory cell during growth inhibition by starvation 下载免费PDF全文
In Chironomus tentans salivary gland cells, the cytoplasm can be dissected into concentric zones situated at increasing distances from the nuclear envelope. After RNA labeling, the newly made ribosomal subunits are found in the cytoplasm mainly in the neighborhood of the nucleus with a gradient of increasing abundance towards the periphery of the cell. The gradient for the small subunit lasts for a few hours and disappears entirely after treatment with puromycin. The large subunit also forms a gradient but one which is only partially abolished by puromycin. The residual gradient which which is resistant to the addition of the drug is probably due to the binding of some large ribosomal units to the membranes of the endoplasmic reticulum (J.-E. Edstrom and u. Lonn. 1976. J. Cell Biol. 70:562-572, and U. Lonn and J.-E. Edstrom. 1976. J. Cell. Biol. 70:573-580). If growth is inhibited by starvation, only the puromycin-sensitive type gradient is observed for the large subunit, suggesting that the attachment of these newly made subunits to the endoplasmic reticulum membranes will not occur. If, on the other hand, the drug-resistant gradient is allowed to form in feeding animals, it is conserved during a subsequent starvation for longer periods than in control feeding animals. This observation provides a further support for an effect of starvation on the normal turnover of the large subunits associated with the endoplasmic reticulum. These results also indicate a considerable structural stability in the cytoplasm of these cells worth little or no gross redistribution of cytoplasmic structures over a period of at least 6 days. 相似文献
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Baart GJ Zomer B de Haan A van der Pol LA Beuvery EC Tramper J Martens DE 《Genome biology》2007,8(7):R136
Background
Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. In general, most of the recent work on N. meningitidis focuses on potential antigens and their functions, immunogenicity, and pathogenicity mechanisms. Very little work has been carried out on Neisseria primary metabolism over the past 25 years. 相似文献9.
Eoghan M Cunnane John JE Mulvihill Hilary E Barrett Michael T Walsh 《Biomedical engineering online》2015,14(Z1):S7
Background
Due to the limited number of experimental studies that mechanically characterise human atherosclerotic plaque tissue from the femoral arteries, a recent trend has emerged in current literature whereby one set of material data based on aortic plaque tissue is employed to numerically represent diseased femoral artery tissue. This study aims to generate novel vessel-appropriate material models for femoral plaque tissue and assess the influence of using material models based on experimental data generated from aortic plaque testing to represent diseased femoral arterial tissue.Methods
Novel material models based on experimental data generated from testing of atherosclerotic femoral artery tissue are developed and a computational analysis of the revascularisation of a quarter model idealised diseased femoral artery from a 90% diameter stenosis to a 10% diameter stenosis is performed using these novel material models. The simulation is also performed using material models based on experimental data obtained from aortic plaque testing in order to examine the effect of employing vessel appropriate material models versus those currently employed in literature to represent femoral plaque tissue.Results
Simulations that employ material models based on atherosclerotic aortic tissue exhibit much higher maximum principal stresses within the plaque than simulations that employ material models based on atherosclerotic femoral tissue. Specifically, employing a material model based on calcified aortic tissue, instead of one based on heavily calcified femoral tissue, to represent diseased femoral arterial vessels results in a 487 fold increase in maximum principal stress within the plaque at a depth of 0.8 mm from the lumen.Conclusions
Large differences are induced on numerical results as a consequence of employing material models based on aortic plaque, in place of material models based on femoral plaque, to represent a diseased femoral vessel. Due to these large discrepancies, future studies should seek to employ vessel-appropriate material models to simulate the response of diseased femoral tissue in order to obtain the most accurate numerical results.10.