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排序方式: 共有1113条查询结果,搜索用时 15 毫秒
101.
Chamorovsky SK Chamorovsky CS Knox PP Chizhov IV Zubov BV 《European biophysics journal : EBJ》2007,36(6):601-608
Laser-induced temperature jump experiments were used for testing the rates of thermoinduced conformational transitions of
reaction center (RC) complexes in chromatophores of Chromatium minutissimum. The thermoinduced transition of the macromolecular RC complex to a state providing effective electron transport from the
multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220–280 K accounts for tens of seconds with activation
energy 0.166 eV/molecule. The rate of the thermoinduced transition in the cytochrome–RC complex was found to be three orders
of magnitude slower than the rate of similar thermoinduced transition of the electron transfer reaction from the primary to
secondary quinone acceptors studied in the preceding work (Chamorovsky et al. in Eur Biophys J 32:537–543, 2003). Parameters of thermoinduced activation of the electron transfer from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer are discussed in terms of cytochrome c docking onto the RC. 相似文献
102.
Xenopus violet cone opsin (VCOP) and its counterion variant (VCOP-D108A) are expressed in mammalian COS1 cells and regenerated with 11-cis-retinal. The phototransduction process in VCOP-D108A is investigated via cryogenic electronic spectroscopy, homology modeling, molecular dynamics, and molecular orbital theory. The VCOP-D108A variant is a UV-like pigment that displays less efficient photoactivation than the mouse short wavelength sensitive visual pigment (MUV) and photobleaching properties that are significantly different. Theoretical calculations trace the difference to the protonation state of the nearby glutamic acid residue E176, which is the homology equivalent of E181 in rhodopsin. We find that E176 is negatively charged in MUV but neutral (protonated) in VCOP-D108A. In the dark state, VCOP-D108A has an unprotonated Schiff base (SB) chromophore (lambdamax = 357 nm). Photolysis of VCOP-D108A at 70 K generates a bathochromic photostationary state (lambdamax = 380 nm). We identify two lumi intermediates, wherein the transitions from batho to the lumi intermediates are temperature- and pH-dependent. The batho intermediate decays to a more red-shifted intermediate called lumi I. The SB becomes protonated during the lumi I to lumi II transition. Decay of lumi II forms meta I, followed by the formation of meta II. We conclude that even in the absence of a primary counterion in VCOP-D108A, the SB becomes protonated during the photoactivation cascade. We examine the relevance of this observation to the counterion switch mechanism of visual pigment activation. 相似文献
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105.
RNA interference (RNAi) is widely used in Caenorhabditis elegans to identify gene function and has been adapted as a high-throughput screening method to identify genes involved in essential processes. The technique has been applied to parasitic nematodes with variable success and we believe that inconsistent outcomes preclude its use as a robust screen with which to identify potential control targets. In this article, key issues that require clarification are discussed, including the mode of delivery of double-stranded RNA to the parasite, the developmental stage targeted and, perhaps of most importance, whether the RNAi pathway (as defined by studies in C. elegans) is fully functional in some parasitic nematodes. 相似文献
106.
Meegan MJ Barrett I Zimmermann J Knox AJ Zisterer DM Lloyd DG 《Journal of enzyme inhibition and medicinal chemistry》2007,22(5):655-666
A series of novel benzothiepin-derived compounds are described as potent selective modulators of the human estrogen receptor (SERMs). The objective of the study is to evaluate the antiproliferative effects of the compounds on human MCF-7 breast tumor cells. These heterocyclic compounds contain the traditional triarylethylene arrangement exemplified by tamoxifen, conformationally restrained through the incorporation of the benzothiepin ring system. The compounds demonstrated potency at nanomolar concentrations in antiproliferative assays against an MCF-7 human breast cancer cell line with low cytotoxicity. The compounds exhibited low nanomolar binding affinity for the estrogen receptor (ER) with some specificity for ERbeta, and also demonstrate potent antiestrogenic properties in the human uterine Ishikawa cell line. The effect of a number of functional group substitutions on the ER binding properties of the benzothiepin molecular scaffold is explored through a brief computational structure-activity relationship investigation with molecular simulation. 相似文献
107.
Knox Peter P. Lukashev Eugene P. Korvatovskii Boris N. Seifullina Nuranija Kh. Goryachev Sergey N. Allakhverdiev Elvin S. Paschenko Vladimir Z. 《Biochemistry. Biokhimii?a》2022,87(10):1138-1148
Biochemistry (Moscow) - Effect of dipyridamole (DIP) at concentrations up to 1 mM on fluorescent characteristics of light-harvesting complexes LH2 and LH1, as well as on conditions of... 相似文献
108.
109.
Hu L Wu X Han J Chen L Vass SO Browne P Hall BS Bot C Gobalakrishnapillai V Searle PF Knox RJ Wilkinson SR 《Bioorganic & medicinal chemistry letters》2011,21(13):3986-3991
A series of nitrobenzyl phosphoramide mustards and their analogs was designed and synthesized to explore their structure-activity relationships as substrates of nitroreductases from Escherichia coli and trypanosomes and as potential antiproliferative and antiparasitic agents. The position of the nitro group on the phenyl ring was important with the 4-nitrobenzyl phosphoramide mustard (1) offering the best combination of enzyme activity and antiproliferative effect against both mammalian and trypanosomatid cells. A preference was observed for halogen substitutions ortho to benzyl phosphoramide mustard but distinct differences were found in their SAR of substituted 4-nitrobenzyl phosphoramide mustards in E. coli nitroreductase-expressing cells and in trypanosomatids expressing endogenous nitroreductases. 相似文献
110.
Ricardo A. Scrosati Amanda S. Knox Nelson Valdivia Markus Molis 《Helgoland Marine Research》2011,65(2):91-102
Environmental stress affects species richness and diversity in communities, but the precise form of the relationship is unclear.
We tested an environmental stress model (ESM) that predicts a unimodal pattern for total richness and diversity in local communities
across the full stress gradient where a regional biota can occur. In 2008, we measured richness and diversity (considering
all macrobenthic species) across the entire intertidal range on three rocky shores on Helgoland Island, Germany. Intertidal
elevation is known to be positively related to abiotic stress. Since Helgoland is between the northern and southern biogeographic
boundaries for the cold-temperate NE Atlantic intertidal biota, it exhibits low stress levels for this biota at low elevations
and high stress at high elevations because of long (>6 h) emersion times. Thus, we predicted a unimodal trend for richness
and diversity across elevation. On all three shores, richness increased from high to middle elevations, but remained similar
between middle and low elevations. Diversity followed the same trend on one shore and different trends (although also non-unimodal)
on the other two. Evenness explained the trend differences between richness and diversity. Overall, our study yielded little
support for the ESM. Reasons for richness and diversity not decreasing at low elevations may be related to influences of mostly
subtidal species, Helgoland’s intertidal range, or sampling resolution. Our study also suggests that the ESM must be developed
further to differentiate between richness and diversity. We offer recommendations to improve future ESM research using intertidal
systems. 相似文献