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191.
192.
Mesenchymal cells (fibroblasts, smooth muscle cells) and endothelial cells were shown to interact with elastin fibers. The strong adhesion of elastin fibers to these cells is mediated by a cell membrane complex with a major glycoprotein component of 120 kDa designated as elastonectin. This interaction was studied by transmission electron microscopy (TEM) and immunocytochemical techniques using antibodies raised against the elastin adhesive proteins. When fibroblasts and smooth muscle cells were cultured in presence of elastin fibers, TEM showed an adhesion mechanism that takes place over several sites along the plasma membrane of these cells. Endothelial cells showed a very close association with elastin, emitting “pseudopodia” that embody the fibers. TEM, indirect immunofluorescence, immunoperoxidase, and confocal microscopy showed the presence and localization of cell membrane components synthesized in large quantities when cells were incubated in presence of elastin. Cells without elastin fibers barely revealed the adhesive membrane complex. These results confirm and extend previous findings concerning the presence of an inducible cell membrane complex that mediates the adhesion of elastin fibers to these cell types. © 1994 Wiley-Liss, Inc.  相似文献   
193.
Abstract: The excitatory amino acid analogues l -glutamate ( l -Glu), l -aspartate ( l -Asp), d -Asp, and trans -(±)-1-amino-1,3-cyclopentanedicarboxylate ( trans -ACPD) stimulate the hydrolysis of phosphoinositides (PI). In the present studies, the effects of noncompetitive and competitive inhibitors on PI hydrolysis stimulated by excitatory amino acid analogues were examined. When agonist and inhibitor were added simultaneously to hippocampal tissue, the noncompetitive inhibitor l -2-amino-3-phosphonopropionate ( l -AP3) did not block the effects of l -Glu, l -Asp, or d -Asp at concentrations that block the effects of trans -ACPD by more than 80%. When tissue was pre-incubated with l -AP3, the effects of l -Glu, l -Asp, or d -Asp were blocked (IC50 values between 65 and 210 µ M ). Unlike l -AP3, l -aspartate-β-hydroxamate ( l -AβHA) inhibited PI hydrolysis stimulated by trans -ACPD, l -Glu, l -Asp, or d -Asp when agonist and inhibitor were added simultaneously in hippocampus; its effects were not time-dependent. In cerebellum, both l -AP3 and l -AβHA had agonist activity. Inhibition by the recently identified competitive inhibitor (+)-α-methyl-4-carboxyphenylglycine [(+)-MCPG] of PI hydrolysis was also examined. (+)-MCPG blocked PI hydrolysis stimulated by trans -ACPD, l -Asp, or d -Asp in both hippocampus and cerebellum (IC50 values between 220 and 1,700 µ M ). The effects of (+)-MCPG were consistent with a competitive mechanism of action. (+)-MCPG (up to 3 m M ) blocked PI hydrolysis stimulated by l -Glu by less than 25% in both hippocampus and cerebellum.  相似文献   
194.
Louis Trabaud 《Oecologia》1994,99(3-4):379-386
The effects of burning on plant nutrient budgets and rates of carbonic gas and particulate matter emission during fires were evaluated in aQuercus coccifera (garrigue) shrubland. Nutrient levels were determined in field-collected pre-fire vegetation and combustion residues. The losses (increased elemental transfer) were calculated as the difference between the quantity of an element in the fuel (combustible standing vegetation plus litter) before burning and that present in the postfire residues (ash). Weight losses of elements are correlated with weight losses of burnt plant biomass. The relative order of nutrient losses was: N>C>Na>Ca>P>K>Mg. Estimated losses of N, C and P from combustible plant matter exceeded 98, 97 and 79% respectively. Copious N, C and P volatilization during burning was promoted by high concentrations of these elements in foliage and fine woody biomass of the aboveground vegetation and leaf litter of the garrigue. Elements were principally removed in the smoke. The quantities of gaseous emissions of CO2, CO and particulate matter produced were estimated.  相似文献   
195.
EPR spectroscopy is a powerful tool to identify at a molecular level, the different steps of catalyst preparation, and of catalytic reactions:
  1. Deposition of paramagnetic transition metal ions onto a support is monitored, and the coordination sphere of the metallic center is characterized by EPR.
  2. The catalyst is also characterized after activation (thermal oxidation or reduction):
  • - the distribution among the different sites in zeolites can be determined;
  • - the dispersion of the active phase may be appreciated;
  • - the unsaturation degree of the active site may be evaluated using probe molecules such as water or13C enriched carbon monoxide.
    1. The catalytic mechanisms can be investigated by studying the elementary steps of the catalytic reaction, as illustrated for methanol oxidation over Mo/SiO2 catalysts whose EPR results have extended the reaction mechanism proposed on the basis of kinetic data. In addition, reaction intermediates may be isolated inquasi-in situ conditions as in the case of olefin oligomerization catalyzed by Ni/SiO2 systems.
      相似文献   
    196.
    Envelope glycoproteins of human immunodeficiency viruses (HIV-1and HIV-2) can interact with high-mannose glycans and with themannosyl or N-acetylglucosaminyl core of complex-type oligosaccharidicstructures. HIV-1 glycoproteins also specifically bind sulphatedpolysaccharides such as dextran sulphate (DS) and heparin. Here,we show that the latter property is shared by HIV-2 recombinantgp140 (rgpl40) precursor glycoprotein. Binding of rgpl40 andof corresponding rgp160 of HIV-1 to heparin- and DS-substituted(sulphated dextran beads; SDB) affinity matrices was inhibitedby the soluble specific ligand and also by fetuin, asialofetuinor the anionic simple carbohydrate derivative manncsse-6-phosphate(M6P). Interaction of HIV-1 rgpl20 subunit with the two affinitymatrices was also inhibited by M6P, but only rgpl20 bindingto heparin-agarose, and not that to SDB, was affected by fetuinand asialofetuin. These results suggest that HIV-1 and HIV-2envelope glycoproteins presumably display different sulphatedpolysaccharide and carbohydrate recognition sites. Some of thesemay be common or in close proximity: with respect to rgpl60,for example, the sites may be common on the gp41 moiety and/orin a region of gp120 which would be more accessible when expressedon rgpl60 than on processed gpl20, while they may be distincton the cleaved gpl20 subunit. Finally, because M6P is a markerof lysosomal enzymes, we verified that HIV-1 and HIV-2 envelopeglycoproteins could specifically bind in a M6P-inhibitable mannerto a representative lysosomal enzyme, bovine liver ß-glucuronidasecoupled to agarose, suggesting that they may possibly interferewith lysosomal enzyme sorting in HIV-infected cells. env glycoproteins HIV lectin mannose-6-phosphate sulphated polysaccharides  相似文献   
    197.
    Most species of the genus Aeromonas produce the siderophore amonabactin, although two species produce enterobactin, the siderophore of many enteric bacteria. Both siderophores contain 2,3-dihydroxybenzoic acid (2,3-DHB). Siderophore genes (designated aebC, -E, -B and -A, for aeromonad enterobactin biosynthesis) that complemented mutations in the enterobactin genes of the Escherichia coli 2,3-DHB operon, entCEBA(P15), were cloned from an enterobactin-producing isolate of the Aeromonas spp. Mapping of the aeromonad genes suggested a gene order of aebCEBA, identical to that of the E. coli 2,3-DHB operon. Gene probes for the aeromonad aebCE genes and for amoA (the entC-equivalent gene previously cloned from an amonabactin-producing Aeromonas spp.) did not cross-hybridize. Gene probes for the E. coli 2,3-DHB genes entCEBA did not hybridize with Aeromonas spp. DNA. Therefore, in the genus Aeromonas, 2,3-DHB synthesis is encoded by two distinct gene groups; one (amo) is present in the amonabactin-producers, while the other (aeb) occurs in the enterobactin-producers. Each of these systems differs from (but is functionally related to) the E. coli 2,3-DHB operon. These genes may have diverged from an ancestral group of 2,3-DHB genes.  相似文献   
    198.
    Human Genetics - Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Analysis of DNA from a pancreatic sufficient patient by means of...  相似文献   
    199.
    200.
    Abstract Release of lipopolysaccharide from E. coli was studied in the presence of sub-minimal inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA). In untreated cells no release was detected with 50 mM Mg2+ in the medium, but a steady release of over 50% of the synthesized lipopolysaccharide was observed with 0.1 mM Mg2+. EDTA at MIC/8 led to a 2- to 3-fold higher release, presumably by an adjustment of the concentration of unchelated Mg2+ to a value still sustaining normal growth but giving rise to a highly unstable outer membrane. No structural difference was observed between cell-bound and released lipopolysaccharide.  相似文献   
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