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排序方式: 共有102条查询结果,搜索用时 15 毫秒
1.
E Arystarkhova M Gasparian N N Modyanov K J Sweadner 《The Journal of biological chemistry》1992,267(19):13694-13701
The Na,K-stimulated ATPase is inhibited by extracellular cardiac glycosides, which bind to the enzyme's alpha subunit. We used a monoclonal antibody, VG4, as a probe of the extracellular surface. The antibody was specific for Na,K-ATPase and bound to intact cells. The epitope was mapped to the first extracellular loop (H1-H2) of alpha, using a combination of techniques including trypsinolysis, N-terminal sequence of a fragment containing the determinant, and analysis of the effects of species-specific sequence differences. The antibody inhibited Na,K-ATPase activity under certain circumstances, indicating that the H1-H2 loop participates in conformational changes that are transmitted to the active site. Mutations in the H1-H2 loop have been shown by others to affect ouabain affinity. Ouabain and the antibody acted synergistically to inhibit the enzyme, which seemingly supported the hypothesis that the H1-H2 loop is an essential part of the cardiac glycoside binding site. Direct measurements of the binding of [3H]ouabain, however, indicated that VG4 enhanced rather than inhibited binding, presumably by promoting favorable conformation changes. The data suggest the possibility that the cardiac glycoside binding site may be intramembrane rather than extracellular. 相似文献
2.
蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化 总被引:2,自引:0,他引:2
蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤. 相似文献
3.
Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution 总被引:37,自引:20,他引:17
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By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus. 相似文献
4.
An attempt is made to reconstitute the Na+-conductivity elements of rod outer segment (ROS) plasma membrane on the artificial lipid membrane (ALM). ALM were modified by preparation with bovine ROS plasma membrane fragments. Discrete fluctuations of the ALM conductivity were observed at addition of this preparation to the ALM bathing solutions to a final concentration of 0.1--1.0 microgram/ml. The magnitude of these fluctuations was about 25 pS at 140 mM NaCl. The modified ALM possessed preferentially the Na+-conductivity, which was at least five times as great as that for K+ or Li+. The modified ALM showed practically no conductivity for Cl-. The Na+-channels were voltage-dependent. The Na+-channels were "sensitive to visible light" at some experimental conditions. The optimal conditions were obtained for reconstitution of Na+-channel on the ALM. The temporal and termal stabilities of the modified preparation were investigated. It was shown that the frequency of the modified ALM conductivity fluctuations are dependent on temperature and on lipids composition of ALM. The data obtained in our work are in a good agreement with the results of electrophysiological studies of photoreceptor cells. It may be indicated, that the investigated ALM contains the Na+-channel of the ROS plasma membranes. It is suggested that the reconstituted system will be useful for studying the principles of regulation of ROS plasma membrane sodium conductivity and the nature of a mediator in a photoreceptor transduction mechanism. 相似文献
5.
Phylogenetic relationships were determined for 76 partial P-element
sequences from 14 species of the melanogaster species group within the
Drosophila subgenus Sophophora. These results are examined in the context
of the phylogeny of the species from which the sequences were isolated.
Sequences from the P-element family fall into distinct subfamilies, or
clades, which are often characteristic for particular species subgroups.
When examined locally among closely related species, the evolution of P
elements is characterized by vertical transmission, whereby the P-element
phylogeny traces the species phylogeny. On a broader scale, however, the
P-element phylogeny is not congruent with the species phylogeny. One
feature of P-element evolution in the melanogaster group is the presence of
more than one P-element subfamily, differing by as much as 36%, in the
genomes of some species. Thus, P elements from several individual species
are not monophyletic, and a likely explanation for the incongruence between
P-element and species phylogenies is provided by the comparison of
paralogous sequences. In certain instances, horizontal transfer seems to be
a valid alternative explanation for lack of congruence between species and
P-element phylogenies. The canonical P-element subfamily, which represents
the active, autonomous transposable element, is restricted to D.
melanogaster. Thus, its origin clearly lies outside of the melanogaster
species group, consistent with the earlier conclusion of recent horizontal
transfer.
相似文献
6.
As was reported elsewhere (Gasparian, Grigorian, 1989a, 1989b), the stimulation of cell proliferation takes place in established culture of chick embryo cells after adding a suspension of living or inactivated homologous cells. In the present paper the kinetic parameters of this process, termed as the contact stimulation of cell proliferation, were studied. The dose- and time-dependence of cell response to the stimulus is described. It was shown that the addition of cells activates cell growth both in exponential and stationary cultures. DNA synthesis in resting cells is seen initiated only if their continuous interaction with the added cells is provided. The nature of signals involved in the process of contact stimulation is described. 相似文献
7.
Jose MG Vilar 《BMC systems biology》2010,4(1):152
Background
Cellular responses to death-promoting stimuli typically proceed through a differentiated multistage process, involving a lag phase, extensive death, and potential adaptation. Deregulation of this chain of events is at the root of many diseases. Improper adaptation is particularly important because it allows cell sub-populations to survive even in the continuous presence of death conditions, which results, among others, in the eventual failure of many targeted anticancer therapies. 相似文献8.
9.
10.
Alessandro S Guimarães Filipe B Carmo Marcos B Heinemann Ricardo WD Portela Roberto Meyer Andrey P Lage Núbia Seyffert Anderson Miyoshi Vasco Azevedo Aurora MG Gouveia 《BMC veterinary research》2011,7(1):1-5