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排序方式: 共有91条查询结果,搜索用时 15 毫秒
1.
Complement proteins C5b-9 induce transbilayer migration of membrane phospholipids. 总被引:2,自引:0,他引:2
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Transbilayer migration of membrane phospholipid arising from membrane insertion of the terminal human complement proteins has been investigated. Asymmetric vesicles containing pyrene-labeled phosphatidylcholine (pyrenePC) concentrated in the inner monolayer were prepared by outer monolayer exchange between pyrenePC-containing large unilamellar vesicles and excess (unlabeled) small unilamellar vesicles, using bovine liver phosphatidylcholine-specific exchange protein. After depletion of pyrenePC from the outer monolayer, the asymmetric large unilamellar vesicles were isolated by gel filtration and exposed to the purified C5b-9 proteins at 37 degrees C. Transbilayer exchange of phospholipid between inner and outer monolayers during C5b-9 assembly was monitored by changes in pyrene excimer and monomer fluorescence. Membrane deposition of the C5b67 complex (by incubation with C5b6 + C7) caused no change in pyrenePC fluorescence. Addition of C8 to the C5b67 vesicles resulted in a dose-dependent decrease in the excimer/monomer ratio. This change was observed both in the presence and absence of complement C9. No change in fluorescence was observed for control vesicles exposed to C8 (in the absence of membrane C5b67), or upon C5b-9 addition to vesicles containing pyrenePC symmetrically distributed between inner and outer monolayers. These data suggest that a transbilayer exchange of phospholipid between inner and outer monolayers is initiated upon C8 binding to C5b67. The fluorescence data were analyzed according to a "random walk" model for excimer formation developed for the case where pyrenePC is asymmetrically distributed between lipid bilayers. Based on this analysis, we estimate that a net transbilayer migration of approximately 1% of total membrane phospholipid is initiated upon C8 binding to C5b67. The potential significance of this transbilayer exchange of membrane phospholipid to the biological activity of the terminal complement proteins is considered. 相似文献
2.
Pollen precedence and stigma closure: a mechanism of competition for pollination between Delphinium nelsonii and Ipomopsis aggregata 总被引:1,自引:0,他引:1
Summary Previous experiments showed that the sympatric herbs Delphinium nelsonii and Ipomopsis aggregata compete for hummingbird pollination and that deleterious effects of the former species on seed set of the latter involve interspecific pollen transfer. However, seed set was not reduced when pollen of both species was applied simultaneously to I. aggregata stigmas. Hence a competitive effect may require arrival of foreign pollen before conspecific pollen. To explore this possibility we subjected I. aggregata flowers to a competition treatment in which they received D. nelsonii pollen 6 h before I. aggregata pollen, or to a control in which they received only the conspecific pollen. Foreign pollen precedence decreased mean seed set by almost 50%, which is consistent with effects observed in previous experiments. Reduced seed set can be explained by the fact that foreign pollen often caused stigma lobes to close together within 1.5–6 h, reducing subsequent receptivity. Stigma closure was also elicited by conspecific pollen, but not by mechanical stimulation, and was influenced by size of the pollen load and identity of the plant being pollinated. 相似文献
3.
Dr AR Holmes RD Cannon HF Jenkinson 《Journal of industrial microbiology & biotechnology》1995,15(3):208-213
The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed. 相似文献
4.
Cytoplasmic domain of P-selectin (CD62) contains the signal for sorting into the regulated secretory pathway. 总被引:29,自引:3,他引:26
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M Disdier J H Morrissey R D Fugate D F Bainton R P McEver 《Molecular biology of the cell》1992,3(3):309-321
P-selectin (CD62), formerly called GMP-140 or PADGEM, is a membrane protein located in secretory storage granules of platelets and endothelial cells. To study the mechanisms responsible for the targeting of P-selectin to storage granules, we transfected its cDNA into COS-7 and CHO-K1 cells, which lack a regulated exocytic pathway, or into AtT20 cells, which are capable of regulated secretion. P-selectin was expressed on the plasma membrane of COS-7 and CHO-K1 cells but was concentrated in storage granules of AtT20 cells. Immunogold electron microscopy indicated that the electron-dense granules containing P-selectin in AtT20 cells also stored the endogenous soluble hormone ACTH. Activation of AtT20 cells with 8-Br-cAMP increased the surface expression of P-selectin, consistent with agonist-induced fusion of granule membranes with the plasma membrane. Deletion of the last 23 amino acids of the 35-residue cytoplasmic domain resulted in delivery of P-selectin to the plasma membrane of AtT20 cells. Replacement of the cytoplasmic tail of tissue factor, a plasma membrane protein, with the cytoplasmic domain of P-selectin redirected the chimeric molecule to granules. We conclude that the cytoplasmic domain of P-selectin is both necessary and sufficient for sorting of membrane proteins into the regulated pathway of secretion. 相似文献
5.
Control of cell volume in the J774 macrophage by microtubule disassembly and cyclic AMP 总被引:8,自引:5,他引:3
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We have explored the possibilities that cell volume is regulated by the status of microtubule assembly and cyclic AMP metabolism and may be coordinated with shape change. Treatment of J774.2 mouse macrophages with colchicine caused rapid microtubule disassembly and was associated with a striking increase (from 15-20 to more than 90 percent) in the proportion of cells with a large protuberance at one pole. This provided a simple experimental system in which shape changes occurred in virtually an entire cell population in suspension. Parallel changes in cell volume could then be quantified by isotope dilution techniques. We found that the shape change caused by colchicine was accompanied by a decrease in cell volume of approximately 20 percent. Nocodozole, but not lumicolchicine, caused identical changes in both cell shape and cell volume. The volume loss was not due to cell lysis nor to inhibition of pinocytosis. The mechanism of volume loss was also examined. Colchicine induced a small but reproducible increase in activity of the ouabain-sensitive Na(+), K(+)-dependent ATPase. However, inhibition of this enzyme/transport system by ouabain did not change cell volume nor did it block the colchicines-induced decrease in volume. One the other hand, SITS (4’acetamido, 4-isothiocyano 2,2’ disulfonic acid stilbene), an inhibitor of anion transport, inhibited the effects of colchicines, thus suggesting a role for an anion transport system in cell volume regulation. Because colchicine is known to activate adenylate cyclase in several systems and because cell shape changes are often induced by hormones that elevate cyclic AMP, we also examined the effects of cyclic AMP on cell volume. Agents that act to increase syclic AMP (cholera toxin, which activates adenylate cyclase; IBMX, and inhibitor of phosphodiesterase; and dibutyryl cyclic AMP) all caused a volume decrease comparable to that of colchicine. To define the effective metabolic pathway, we studied two mutants of J774.2, one deficient in adenylate cyclase and the other exhibiting markedly reduced activity of cyclic AMP-dependent protein kinase. Cholera toxin did not produce a volume change in either mutant. Cyclic AMP produced a decrease in the cyclase-deficient line comparable to that in wild type, but did not cause a volume change in the kinase- deficient line. This analysis established separate roles for cyclic AMP and colchicine. The volume decrease induced by cyclic AMP requires the action of a cyclic AMP-dependent protein kinase. Colchicine, on the other hand, induced a comparable volume change in both mutants and wild type, and thus does not require the kinase. 相似文献
6.
Relative rates of repair of single-strand breaks and postirradiation DNA degradation in normal and induced cells of Escherichia coli.
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Labeled DNA from irradiated Excherichia coli cells has been studied on an alkaline sucrose gradient without acid precipitation of the DNA. This enables the observation of both DNA repair and DNA degradation. The use of a predose of ultraviolet light (UV) causes induction of an inhibitor of postirradiation DNA degradation in lex+ strains. The effect of this induction on both the repair of single-strand breaks and DNA degradation has been followed in strains WU3610 (uvr+) and WU3610-89 (uvr-). The repair process is more rapid than the degradation, and when degradation is inhibited more repair is apparent. Cells that are lex- (Bs-1 and AB2474) cannot be induced for inhibition of degradation. Nevertheless, by observation at short times repair can be seen clearly. This repaired DNA is degraded, suggesting that the signal for DNA degradation is not a single-strand break. 相似文献
7.
Membrane behavior of exocytic vesicles: II in fate of the trichocyst membranes in paramecium after induced trichocyst discharge
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A specific exocytic process, the discharge of spindle trichocysts of paramecium caudatum was examined by means of the electron microscope. This exocytosis is induced by an electric shock simultaneously in nearly all of the trichocysts (ca. 6,000-8,0000 of a single cell. Single paramecia were subjected to the shock and then fixed at defined times after the shock so that the temporal sequence of the pattern of changes of the trichocyst membranes after exocytosis could be studied. The trichocyst vacuoles fuse with the plasma membrane only for that length of time required for expulsion to take place. After exocytosis, the membrane of the vacuole does not become incorporated into the plasma membrane; rather, the collapsed vacuole is pinched off and breaks up within the cytoplasm. The membrane vesiculates into small units which can no longer be distinguished from vesicles of the same dimensions that exist normally within the cell's cytoplasm. the entire process is completed within 5-10 min. These results differ from the incorporation of mucocyst membranes into the plasma membrane as proposed for tetrahymena. 相似文献
8.
METTE SERINE WESMAJERVI TEKLE TAFESE J
RGEN STENVIK KJERSTI TURID FJALESTAD B
RGE DAMSGRD MADJID DELGHANDI 《Molecular ecology resources》2007,7(1):138-140
One hundred and fifty random clones from an enriched genomic library of Atlantic cod were sequenced. Primer pairs were designed for 15 microsatellites containing perfect di‐, tri‐, tetra‐ and hexanucleotide repeats and characterized in 96 unrelated fish. Eight markers were successfully amplified, with the number of alleles ranging from two to nine per locus and observed heterozygosity ranging from 0.341 to 0.977. Loci Gmo‐G13 and Gmo‐G14 had a significant excess of homozygotes. All loci conformed to the Hardy–Weinberg equilibrium. Genetic linkage disequilibrium analysis between all pairs of the loci showed no significant departure from the null hypothesis between any of the loci. 相似文献
9.
Chintamani Sharma R Badran R Singhal V Saxena S Bansal A 《World journal of surgical oncology》2003,1(1):13
Background
Sweat gland adenocarcinoma is a rare malignancy with high metastatic potential seen more commonly in later years of life. Scalp is the most common site of occurrence and it usually spreads to lymph nodes. Liver, lung and bones are the distant sites of metastasis with fatal results. The differentiation between apocrine and eccrine metastatic sweat gland carcinoma is often difficult. The criteria's are inadequate to be of any practical utility. 相似文献10.