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排序方式: 共有393条查询结果,搜索用时 15 毫秒
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A homeomorphic mathematical model of cell surface insulin receptor regulation is developed. The overall structure of the model is based on molecular mechanisms suggested by in vivo and in vitro experimental evidence from many different cell types. Model parameters correspond to cellular processes which are constrained by known boundry value conditions. As an example, computer simulation results are compared with published data from BC3H-1 myocytes in culture. With appropriate parameter choice, this model is able to simulate data from other cell types. Cellular processes which are explicitly represented in the model include: bound and unbound receptor endocytosis, receptor recycling, intracellular receptor degradation, and state-dependent receptor synthesis. Most of these processes are represented as first-order events. Using more complex representations of the model structure with higher order rate constants or saturable pathways does not qualitatively improve simulation results. Simulations are able to reproduce ligand-induced down and up regulation of receptors as well as the initial spontaneous display of surface insulin receptors. To demonstrate the behavior of our model and illustrate its utility for explaining insulin receptor regulation for a variety of conditions, simulations for which experimental data is unavailable for direct comparison are also shown. We believe the structure of our model is sufficient to explain insulin receptor regulation in a wide variety of cell types. In addition our model may aid in understanding the receptor component of insulin resistance (decreased sensitivity or responsiveness to insulin) seen in pathological states such as obesity and diabetes mellitus. Finally, this model may be applicable to the study of the regulation of other polypeptide hormone receptors. 相似文献
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Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells
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A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species. 相似文献
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Deep-level diagnostic value of the rDNA-ITS region 总被引:14,自引:0,他引:14
The similarity of certain reported angiosperm rDNA internal transcribed
spacer (ITS) region sequences to those of green algae prompted our analysis
of the deep-level phylogenetic signal in the highly conserved but short
5.8S and hypervariable ITS2 sequences. We found that 5.8S sequences yield
phylogenetic trees similar to but less well supported than those generated
by a ca. 10-fold longer alignment from rDNA-18S sequences, as well as
independent evidence. We attribute this result to our finding that,
compared to 18S, the 5.8S has a higher proportion of sites subject to vary
and greater among-site substitution rate homogeneity. We also determined
that our phylogenetic results are not likely affected by intramolecular
compensatory mutation to maintain RNA secondary structure nor by evident
systematic biases in base composition. Despite historical homology, there
appears to be no ITS2 primary sequence similarity shared sufficient
similarity to cluster correctly on the basis of alignability. Our results
indicate that groups, however, share sufficient similarity to cluster
correctly on the basis of alignability. Our results indicate that ITS
region sequences can diagnose organismal origins and phylogenetic
relationships at many phylogenetic levels and provide a useful paradigm for
molecular evolutionary study.
相似文献
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Production of Serine Proteases by the Oyster Pathogen Perkinsus marinus (Apicomplexa) In Vitro 总被引:1,自引:1,他引:0
JEROME F. LA PEYRE DORIS Y. SCHAFHAUSER ESAM H. RIZKALLA MOHAMED FAISAL 《The Journal of eukaryotic microbiology》1995,42(5):544-551
ABSTRACT. Analysis of the cell-free supernatants of Perkinsus marinus cultures by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining revealed the presence of as many as 17 bands ranging in molecular weight from 239 to 32 kDa. These bands were not present in un-inoculated medium. Moreover, P. marinus produces extracellular proteins that possess proteolytic activities; the cell-free supernatants of P. marinus cultures could digest a variety of proteins including gelatin, casein, fibronectin and laminin. Oyster plasma was also digested by cell-free culture supernatants. The proteolytic activity in cell-free culture supernatants was detected 24 h post-inoculation, while no proteolytic activity could be detected in cell lysates. The proteolytic activities were characterized using substrate-impregnated sodium dodecylsulfate-polyacrylamide gels and had approximate molecular weights ranging from 55 to 35 kDa. The proteolytic activity of cell-free culture supernatants was inhibited by the serine protease inhibitors phenylmethylsulphonyl fluoride, 3,4-dichloroisocoumarin and soybean trypsin inhibitor. In contrast, inhibitors (i.e. trans-epoxysuccinyll-leucylamido(4-guanidino)-butane, 1, 10-phenanthroline, captopril, ethylenediaminetetracetic acid, pepstatin A or diazoacetyl-DL-norleucine methyl ester) from the other three classes of proteases had no effect. It was concluded that the P. marinus proteases in cell-free culture supernatants are serine proteases. 相似文献
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