排序方式: 共有44条查询结果,搜索用时 250 毫秒
11.
The preservation of ultrastructure in saturated phosphatidyl cholines by tannic acid in model systems and type II pneumocytes 下载免费PDF全文
The preservation for electron microscopy of saturated phospholipids in general, and phosphatidyl choline (PC)in particular, remains and unsolved problem since OsO(4) and glutaraldehyde are incapable of interacting with PC directly. However, by introducing tannic acid preceding osmication, we were able to demonstrate highly ordered, preserved lamellar structures in model experiments with saturated PC, and in vivo experiments type II pneumocytes of lung tissue. The secretory bodies of the latter are known to contain a high proportion of these saturated phospholipids. In both cases, the repeating periodicity approximated 45 A. It was determined that tannic acid interacts with the choline component of PC to form a "complex," which then could be stabilized by treatment with OsO(4). In the absence of osmication, the PC-tannic acid complex acid did not survive conventional dehydration techniques, but osmication permitted conventional Epon embedment. Sphingomyelin (SPH), which contains choline, behaved similarly in model experiments. But there was no evidence of a comparable reaction with tannic acid using phosphatidyl ethanolamine (PEA), phosphatidyl serine (PS), or phosphstidy inositol (PI). Chemical studies indicted a high pH dependency for the formation of the PC- tannic acid complex. Also, experiments demonstrated its dissociation in various organic solvents. Sharp delineation and great contrast of the polar zones in the ordered lamellar structures was achieved by additional staining with lead citrate thus leading to the conclusion that tannic acid serves as a multivalent agent, capable of simultaneous interaction with saturated PC, OsO(4), and lead citrate stains. 相似文献
12.
Cyclic amp-induced morphological transformation of cells infected by temperature-sensitive mouse sarcoma virus: Expression of transformation-associated markers 下载免费PDF全文
Normal rat kidney (NRK) cells infected with a temperature-sensitive (ts) mutant of mouse sarcoma virus (NRK [MSV-1b]) express the transformed phenotype when grown under permissive conditions, but acquire the normal phenotype when grown under restrictive conditions. Addition of 3', 5' cyclic adenosine monophosphate (cAMP) to NRK (MSV-1b) cells grown at the restrictive temperature results in morphological transformation. To determine whether other markers associated with the transformed phenotype were coordinately expressed after cAMP exposure, concanavalin A (Con A) agglutinability, hexose transport rate, and incorporation of radioactively labeled fucose into fucolipid III and fucolipid IV (FL III and FL IV ) of the cells were examined. NRK cells transformed by wild-type MSV or NRK(MSV- 1b) grown under permissive conditions were agglutinated by low concentrations of Con A and exhibited relatively high maximal agglutination levels which were specifically inhibited by α-methyl-D-mannoside. In contrast, NRK (MSV-1b) cells grown under restrictive conditions were weakly agglutinated by Con A and exhibited reduced maximal agglutination levels, similar to uninfected NRK cells. Treatment of NRK (MSV-1b) cells at the restrictive temperature with cAMP resulted in morphological transformation and a change in the pattern of incorporation of labeled fucose inot FL III and FL IV to one comparable to that of NRK (MSV-1b) cells at the permissive temperature or to NRK cells transformed by wild-type MSV. In contrast, cAMP treatment resulted in no increase in Con A agglutinability or 2 deoxy-D- [(3)H]glucose transport relative to mock treated cultures. The results demonstrate that cAMP-induced morphological transformation and altered fucolipid composition of NRK (MSV-1b) cells are not correlated with alterations in hexose transport rate or Con A agglutinability. 相似文献
13.
In situ hybridization at the electron microscope level: hybrid detection by autoradiography and colloidal gold 总被引:14,自引:4,他引:10 下载免费PDF全文
In situ hybridization has become a standard method for localizing DNA or RNA sequences in cytological preparations. We developed two methods to extend this technique to the transmission electron microscope level using mouse satellite DNA hybridization to whole mount metaphase chromosomes as the test system. The first method devised is a direct extension of standard light microscope level using mouse satellite DNA hybridization to whole mount metaphase chromosomes as the test system. The first method devised is a direct extension of standard light microscope in situ hybridization. Radioactively labeled complementary RNA (cRNA) is hybridized to metaphase chromosomes deposited on electron microscope grids and fixed in 70 percent ethanol vapor; hybridixation site are detected by autoradiography. Specific and intense labeling of chromosomal centromeric regions is observed even after relatively short exposure times. Inerphase nuclei present in some of the metaphase chromosome preparations also show defined paatterms of satellite DNA labeling which suggests that satellite-containing regions are associate with each other during interphase. The sensitivity of this method is estimated to at least as good as that at the light microscope level while the resolution is improved at least threefold. The second method, which circumvents the use of autoradiogrphic detection, uses biotin-labeled polynucleotide probes. After hybridization of these probes, either DNA or RNA, to fixed chromosomes on grids, hybrids are detected via reaction is improved at least threefold. The second method, which circumvents the use of autoradiographic detection, uses biotin-labeled polynucleotide probes. After hybridization of these probes, either DNA or RNA, to fixed chromosomes on grids, hybrids are detected via reaction with an antibody against biotin and secondary antibody adsorbed to the surface of over centromeric heterochromatin and along the associated peripheral fibers. Labeling is on average ten times that of background binding. This method is rapid and possesses the potential to allow precise ultrastructual localization of DNA sequences in chromosomes and chromatin. 相似文献
14.
Vetting MW Bareich DC Yu M Blanchard JS 《Protein science : a publication of the Protein Society》2008,17(10):1781-1790
The three ribosomal proteins L7, S5, and S18 are included in the rare subset of prokaryotic proteins that are known to be N(alpha)-acetylated. The GCN5-related N-acetyltransferase (GNAT) protein RimI, responsible for the N(alpha)-acetylation of the ribosomal protein S18, was cloned from Salmonella typhimurium LT2 (RimI(ST)), overexpressed, and purified to homogeneity. Steady-state kinetic parameters for RimI(ST) were determined for AcCoA and a peptide substrate consisting of the first six amino acids of the target protein S18. The crystal structure of RimI(ST) was determined in complex with CoA, AcCoA, and a CoA-S-acetyl-ARYFRR bisubstrate inhibitor. The structures are consistent with a direct nucleophilic addition-elimination mechanism with Glu103 and Tyr115 acting as the catalytic base and acid, respectively. The RimI(ST)-bisubstrate complex suggests that several residues change conformation upon interacting with the N terminus of S18, including Glu103, the proposed active site base, facilitating proton exchange and catalysis. 相似文献
15.
Effect of oxygen tension on human peripheral blood leukocytes: lysosomal enzyme release and metabolic responses during phagocytosis 总被引:2,自引:0,他引:2 下载免费PDF全文
JL Skosey DC Chow S Nusinow J May V Gestautas Y Niwa 《The Journal of cell biology》1981,88(2):358-363
We found that nonlethal lysosomal enzyme release from human peripheral blood leukocytes during phagocytosis of opsonized zymosan in vitro was modified by the oxygen tension under which the cells were incubated; with decreasing Po(2), zymosan-induced release of lysosomal enzymes was potentiated. The effect on enzyme release could not be attributed secondarily to an effect on phagocytosis, because, as others have reported, Po(2) had little effect on that response. Metabolic responses that accompany phagocytosis were also modified by oxygen tension. Stimulation of oxidation by way of the pentose cycle was further enhanced by increasing Po(2). Conversely, anaerobic glycolysis was promoted by decreasing oxygen tension. ATP levels fell as a function of time and concentration of phagocytic stimulus, mirroring lysosomal enzyme release as modified by Po(2). Cyclic AMP levels fell during phagocytosis and lysosomal enzyme release, a change that could act to facilitate lysosomal enzyme release. However, the fall in nucleotide level was greatest with highest Po(2) (i.e., when lysosomal enzyme release was least). The inverse relationship between oxidative metabolism and enzyme release suggested that a product of oxidative metabolism might adversely influence enzyme release. Sulfhydryl antioxidants (Cysteine, glutathione) and scavengers of oxygen-derived reactants (superoxide dismutase, catalase, benzoate, hypoxanthine, xanthine, histidine, azide) all potentiated zymosan- stimulated enzyme release. These findings are consistent with the interpretation that one or more factors (e.g., superoxide anion, hydrogen peroxide, hydroxyl radical, singlet oxygen), generated in association with the burst of oxidative metabolism which accompanies phagocytosis, acts to inhibit lysosomal enzyme release. 相似文献
16.
Yang W Moore IF Koteva KP Bareich DC Hughes DW Wright GD 《The Journal of biological chemistry》2004,279(50):52346-52352
The tetracycline antibiotics block microbial translation and constitute an important group of antimicrobial agents that find broad clinical utility. Resistance to this class of antibiotics is primarily the result of active efflux or ribosomal protection; however, a novel mechanism of resistance has been reported to be oxygen-dependent destruction of the drugs catalyzed by the enzyme TetX. Paradoxically, the tetX genes have been identified on transposable elements found in anaerobic bacteria of the genus Bacteroides. Overexpression of recombinant TetX in Escherichia coli followed by protein purification revealed a stoichiometric complex with flavin adenine dinucleotide. Reconstitution of in vitro enzyme activity demonstrated a broad tetracycline antibiotic spectrum and a requirement for molecular oxygen and NADPH in antibiotic degradation. The tetracycline products of TetX activity were unstable at neutral pH, but mass spectral and NMR characterization under acidic conditions supported initial monohydroxylation at position 11a followed by intramolecular cyclization and non-enzymatic breakdown to other undefined products. TetX is therefore a FAD-dependent monooxygenase. The enzyme not only catalyzed efficient degradation of a broad range of tetracycline analogues but also conferred resistance to these antibiotics in vivo. This is the first molecular characterization of an antibiotic-inactivating monooxygenase, the origins of which may lie in environmental bacteria. 相似文献
17.
Concentric electrodes have been fabricated from 304 stainless steel in which a small anode (0.031 cm2) and large cathode (4.87 cm2) are induced by the application of a current density of 11A cm–2 at the anode. It has previously been shown that reproducible pitting and maintenance of a galvanic current occurs only in the presence of a consortium of bacteria containing sulphate-reducing bacteria (SRB). Actively corroding systems that had maintained a galvanic current for at least 24 h after the applied current was removed were treated with inhibitors of the SRB. The only inhibitor tested which had any marked effect on the galvanic current was sodium molybdate which is a known inhibitor of corrosion as well as SRB. 相似文献
18.
The montane forests of northern Mozambique’s isolated massifs are inhabited by numerous range-restricted and threatened bird species, but until recently were extremely little-known. We report on a first avifaunal survey of the isolated montane habitats of Mt Mecula (1 442 m), Niassa National Reserve, notable as the only currently protected montane area in northern Mozambique. Mount Mecula’s moist forest is small (approximately 136 ha in total) and patchy, and although known botanically to have some montane affinities, was found to support an avifauna more typical of riparian forests of medium to low altitude. The only montane forest species recorded was Lemon Dove Aplopelia larvata. Other montane elements included Vincent’s Bunting Emberiza (capensis) vincenti, one of six species recorded new to the Niassa National Reserve list. Overall, it appears that despite its intermediate location, Mt Mecula does not represent a biogeographical ‘stepping stone’ for montane forest bird species. This probably owes to its remoteness from the Eastern Arc Mountains of Tanzania to the north and the massifs of other parts of northern Mozambique, to the south and west. 相似文献
19.
Angela CM Luyf Barbera DC van Schaik Michel de Vries Frank Baas Antoine HC van Kampen Silvia D Olabarriaga 《BMC bioinformatics》2010,11(1):598
Background
Bioinformatics is confronted with a new data explosion due to the availability of high throughput DNA sequencers. Data storage and analysis becomes a problem on local servers, and therefore it is needed to switch to other IT infrastructures. Grid and workflow technology can help to handle the data more efficiently, as well as facilitate collaborations. However, interfaces to grids are often unfriendly to novice users. 相似文献20.
Ornella J Rullo Jennifer MP Woo Miriam F Parsa Alice DC Hoftman Paul Maranian David A Elashoff Timothy B Niewold Jennifer M Grossman Bevra H Hahn Maureen McMahon Deborah K McCurdy Betty P Tsao 《Arthritis research & therapy》2013,15(1):R18