首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   78篇
  免费   16篇
  2021年   4篇
  2020年   2篇
  2019年   1篇
  2018年   6篇
  2017年   3篇
  2016年   2篇
  2015年   1篇
  2014年   4篇
  2013年   4篇
  2012年   8篇
  2011年   6篇
  2010年   6篇
  2009年   1篇
  2008年   5篇
  2007年   4篇
  2006年   1篇
  2005年   6篇
  2004年   3篇
  2003年   3篇
  2001年   3篇
  2000年   1篇
  1996年   1篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1989年   1篇
  1987年   1篇
  1985年   1篇
  1983年   2篇
  1971年   1篇
  1970年   4篇
  1969年   2篇
  1965年   1篇
排序方式: 共有94条查询结果,搜索用时 31 毫秒
1.
2.
Staphylococcal nuclease, at low pH and in the presence of high salt concentrations, has previously been proposed to exist in a partially folded or molten globule form called the "A-state" (Fink et al., 1993, Protein Sci 2:1155-1160). We have found that the A-state of nuclease at pH 2.1 in the presence of moderate to high salt concentrations and at low temperature exists in a substantially folded form structurally more similar to a native state. The A-state has the far-UV circular dichroism spectra characteristic of the native protein, which indicates that it has a large degree of secondary structure. Upon heating, the A-state denatures with a sigmoidal change in far-UV ellipticity and an observable peak in a differential scanning calorimeter trace, indicating that it is thermodynamically distinct from the denatured state. Three different mutations in a residue normally buried in the protein's core stabilize or destabilize the A-state in the same way as they affect the denaturation of the native state. The A-state must, therefore, contain at least some tertiary packing of side chains. Unlike the native state, which shows cold denaturation at low temperatures, the A-state is most stable at temperatures below 0 degrees C.  相似文献   
3.
Abstract Aeromonas salmonicida grown aerobically in the presence of tyrosine produces a dark-brown pigment, previously considered to be of a melanin type. However, this pigment is very water-soluble in contrast to melanin's solubility. In addition, no evidence for the presence of key early reactions and intermediates of the melanogensis pathway has been obtained. Radioisotopic labelling experiments, spectral data and chromatographic analyses support the conclusion that pigment biosynthesis, from tyrosine by Aeromonas salmonicida differs substantially from that of melanogenesis, and strongly suggest that the first intermediate is 2,4-dihydroxyphenylalanine and not 3,4-dihydroxyphenylalanine.  相似文献   
4.
During aging, oxidized, misfolded, and aggregated proteins accumulate in cells, while the capacity to deal with protein damage declines severely. To cope with the toxicity of damaged proteins, cells rely on protein quality control networks, in particular proteins belonging to the family of heat‐shock proteins (HSPs). As safeguards of the cellular proteome, HSPs assist in protein folding and prevent accumulation of damaged, misfolded proteins. Here, we compared the capacity of all Drosophila melanogaster small HSP family members for their ability to assist in refolding stress‐denatured substrates and/or to prevent aggregation of disease‐associated misfolded proteins. We identified CG14207 as a novel and potent small HSP member that exclusively assisted in HSP70‐dependent refolding of stress‐denatured proteins. Furthermore, we report that HSP67BC, which has no role in protein refolding, was the most effective small HSP preventing toxic protein aggregation in an HSP70‐independent manner. Importantly, overexpression of both CG14207 and HSP67BC in Drosophila leads to a mild increase in lifespan, demonstrating that increased levels of functionally diverse small HSPs can promote longevity in vivo.  相似文献   
5.
We have previously demonstrated that Paracentrotus lividus nuclear genome encodes for the heat shock inducible chaperonin homolog Hsp 56 (1) and that the mature protein is localized in the mitochondrial matrix (2). In this paper we report that constitutive Hsp56 is maternally inherited, in fact it is present in the in unfertilized eggs, and that it has a perinuclear specific localization during cleavage. In the later stages both the constitutive and the heat shock inducible chaperonin has a specific territorial distribution. Moreover following heat shock, the Hsp56 appears in the cytoplasm and in the postmitochondrial supernatant beside the mitochondrial fraction.  相似文献   
6.
Stem slices cut from micropropagated cuttings of apple rootstock M26 were cultured in the presence of indole-3-butyric acid (IBA) plus N,N-bis-(2,3-methylenedioxyphenyl)urea or N,N-bis-(3,4-methylenedioxyphenyl)urea, to verify if there was an interaction between them in enhancing root formation. The N,N-bis-(methylenedioxyphenyl)ureas were supplemented after, before and in the simultaneous presence of auxin. Our data demonstrate that only the simultaneous presence of auxin and N,N-bis-(methylenedioxyphenyl)ureas in the culture medium enhanced root formation on M26 stem slices. The percentage of rooted slices obtained in the presence of the mixtures was significantly different from that obtained in the presence of low auxin concentration alone (1µM). Moreover both the percentage of rooted slices and the number of roots per slice obtained in these culture conditions was not significantly different to that of the optimal auxinic treatment in which the auxin concentration was threefold higher.  相似文献   
7.
Biosynthesis and posttranslational regulation of human IL-12   总被引:6,自引:0,他引:6  
IL-12 is a heterodimeric proinflammatory cytokine consisting of a light alpha-chain, formerly defined as p35, disulfide-linked to a heavier beta-chain, formerly defined as p40. The beta-chain is also produced in large excess in a free form, and disulfide-linked beta-chain homodimers with anti-inflammatory effects are produced in the mouse. We analyzed the biosynthesis and glycosylation of IL-12 in human monocytes, and in a cell line stably transfected with IL-12 alpha and beta genes (P5-0.1). The IL-12 heterodimer and free beta-chain were immunoprecipitated from supernatants and cell lysates of metabolically labeled cells and resolved in SDS-PAGE. Whereas the beta-chain showed similar pI pattern whether in the free form or associated in the heterodimer, either in the secreted or intracellular form, the alpha-chain in the secreted heterodimer was much more acidic than that present in the intracellular heterodimer. Deglycosylation experiments with neuraminidase and Endo-F combined with two-dimensional PAGE of single bands of the intracellular vs extracellular IL-12 heterodimer revealed that the alpha-chain was extensively modified with sialic acid adducts to N-linked oligosaccharides before secretion. N-glycosylation inhibition by tunicamycin (TM) did not alter free beta-chain secretion, while preventing the IL-12 heterodimer assembling and secretion. Pulse-chase experiments indicated that IL-12 persists intracellularly for a long period as an immature heterodimer, and that glycosylation is the regulatory step that determines its secretion. beta-chain disulfide-linked homodimers were observed in TM-treated P5-0.1 cells, but in neither TM-treated nor untreated monocytes.  相似文献   
8.

Background  

Ricin is a potent toxin and known bioterrorism threat with no available antidote. The ricin A-chain (RTA) acts enzymatically to cleave a specific adenine base from ribosomal RNA, thereby blocking translation. To understand better the relationship between ligand binding and RTA active site conformational change, we used a fragment-based approach to find a minimal set of bonding interactions able to induce rearrangements in critical side-chain positions.  相似文献   
9.
Machupo virus (MACV) is a highly pathogenic New World arenavirus that causes hemorrhagic fever in humans. MACV, as well as other pathogenic New World arenaviruses, enter cells after their GP1 attachment glycoprotein binds to their cellular receptor, transferrin receptor 1 (TfR1). TfR1 residues essential for this interaction have been described, and a co-crystal of MACV GP1 bound to TfR1 suggests GP1 residues important for this association. We created MACV GP1 variants and tested their effect on TfR1 binding and virus entry to evaluate the functional significance of some of these and additional residues in human and simian cells. We found residues R111, D123, Y122, and F226 to be essential, D155, and P160 important, and D114, S116, D140, and K169 expendable for the GP1-TfR1 interaction and MACV entry. Several MACV GP1 residues that are critical for the interaction with TfR1 are conserved among other New World arenaviruses, indicating a common basis of receptor interaction. Our findings also open avenues for the rational development of viral entry inhibitors.  相似文献   
10.
Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (VO2), carbon dioxide output (VCO2), and ventilation (VE) during moderate intensity exercise. We did this by comparing the ventilatory time constants (tau) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 +/- 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (VO2max = 55.2 +/- 5.8 ml x min(-1) x kg(-1)). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their VO2max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (VO2, VCO2, and VE) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the tau during phase 2 of VO2 (43.1 +/- 8.6 vs. 60.9 +/- 14.1 s; P < 0.001), VCO2 (60.3 +/- 17.6 vs. 84.5 +/- 18.1 s; P < 0.001) and VE (59.4 +/- 16.1 vs. 85.9 +/- 17.1 s; P < 0.001). The average rise in tau was 41.3% for VO2, 40.1% for VCO2, and 44.6% for VE. The tau changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号