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991.
992.
Pavla Heringova Jana Kasparkova Viktor Brabec 《Journal of biological inorganic chemistry》2009,14(6):959-968
We studied the effect of antitumor cisplatin and inefficient transplatin on the structure and stability of G quadruplexes
formed by the model human telomere sequence 5′-GGG(TTAGGG)3-3′ using circular dichroism, UV-monitored thermal denaturation, and gel electrophoresis. In addition, to investigate whether
there is a connection between the ability of cisplatin or transplatin to affect telomerase activity and stability of G quadruplexes,
we also used a modified telomere repeat amplification protocol assay that uses an oligonucleotide substrate for telomerase
elongation susceptible to forming a G quadruplex. The results indicate that cisplatin is more efficient than transplatin in
disturbing the quadruplex structure, thereby precluding telomeric sequences from forming quadruplexes. On the other hand,
the results of this work also demonstrate that in absence of free platinum complex, DNA adducts of antitumor cisplatin inhibit
telomerase catalysis, so the mechanism underlying this inhibition does not involve formation of the G quadruplexes which are
not elongated by telomerase. 相似文献
993.
994.
Mechanistic studies of the modulation of cleavage activity of topoisomerase I by DNA adducts of mono- and bi-functional PtII complexes
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Using electrophoresis and replication mapping, we show that the presence of DNA adducts of bifunctional antitumor cisplatin or monodentate [PtCl(dien)]Cl (dien = diethylenetriamine) in the substrate DNA inhibits eukaryotic topoisomerase 1 (top1) action, the adducts of cisplatin being more effective. The presence of camptothecin in the samples of platinated DNA markedly enhances effects of Pt–DNA adducts on top1 activity. Interestingly, the effects of Pt–DNA adducts on the catalytic activity of top1 in the presence of camptothecin differ depending on the sequence context. A multiple metallation of the short nucleotide sequences on the scissile strand, immediately downstream of the cleavage site impedes the cleavage by top1. On the other hand, DNA cleavage by top1 at some cleavage sites which were not platinated in their close proximity is notably enhanced as a consequence of global platination of DNA. We suggest that this enhancement of DNA cleavage by top1 may consist in its inability to bind to other cleavage sites platinated in their close neighborhood; thus, more molecules of top1 may become available for cleavage at the sites where top1 normally cleaves and where platination does not interfere. 相似文献
995.
Background and Aims
Cost–benefit models predict that carnivory can increase the rate of photosynthesis (AN) by leaves of carnivorous plants as a result of increased nitrogen absorption from prey. However, the cost of carnivory includes decreased AN and increased respiration rates (RD) of trapping organs. The principal aim of the present study was to assess the costs and benefits of carnivory in the pitcher plant Nepenthes talangensis, leaves of which are composed of a lamina and a pitcher trap, in response to feeding with beetle larvae.Methods
Pitchers of Nepenthes grown at 200 µmol m−2 s−1 photosynthetically active radiation (PAR) were fed with insect larvae for 2 months, and the effects on the photosynthetic processes were then assessed by simultaneous measurements of gas exchange and chlorophyll fluorescence of laminae and pitchers, which were correlated with nitrogen, carbon and total chlorophyll concentrations.Key Results
AN and maximum (Fv/Fm) and effective quantum yield of photosystem II (ΦPSII) were greater in the fed than unfed laminae but not in the fed compared with unfed pitchers. Respiration rate was not significantly affected in fed compared with unfed plants. The unfed plants had greater non-photochemical quenching (NPQ) of chlorophyll fluorescence. Higher NPQ in unfed lamina did not compensate for their lower ΦPSII, resulting in lower photochemical quenching (QP) and thus higher excitation pressure on PSII. Biomass and nitrogen and chlorophyll concentration also increased as a result of feeding. The cost of carnivory was shown by lower AN and ΦPSII in pitchers than in laminae, but RD depended on whether it was expressed on a dry weight or a surface area basis. Correlation between nitrogen and AN in the pitchers was not found. Cost–benefit analysis showed a large beneficial effect on photosynthesis from feeding as light intensity increased from 200 to 1000 µmol m−2 s−1 PAR after which it did not increase further. All fed plants began to flower.Conclusion
Feeding pitchers with insect larvae increases AN of leaf laminae, due to higher nutrient acquisition, with strong correlation with nitrogen concentration, but AN of pitchers does not increase, despite increased nitrogen concentration in their tissue. Increased AN improves growth and reproduction and is likely to increase the competitive advantage of carnivorous over non-carnivorous plants in nutrient-poor habitats.Key words: carnivorous plants, chlorophyll fluorescence, Nepenthes talangensis, nitrogen, pitcher plant, photosynthetic rate, photosystem II, respiration rate 相似文献996.
Ruth Rollason Viktor Korolchuk Clare Hamilton Mark Jepson George Banting 《The Journal of cell biology》2009,184(5):721-736
CD317/tetherin is a lipid raft–associated integral membrane protein with a novel topology. It has a short N-terminal cytosolic domain, a conventional transmembrane domain, and a C-terminal glycosyl-phosphatidylinositol anchor. We now show that CD317 is expressed at the apical surface of polarized epithelial cells, where it interacts indirectly with the underlying actin cytoskeleton. CD317 is linked to the apical actin network via the proteins RICH2, EBP50, and ezrin. Knocking down expression of either CD317 or RICH2 gives rise to the same phenotype: a loss of the apical actin network with concomitant loss of apical microvilli, an increase in actin bundles at the basal surface, and a reduction in cell height without any loss of tight junctions, transepithelial resistance, or the polarized targeting of apical and basolateral membrane proteins. Thus, CD317 provides a physical link between lipid rafts and the apical actin network in polarized epithelial cells and is crucial for the maintenance of microvilli in such cells. 相似文献
997.
Xianming Wang Guofeng Gao Kai Guo Viktor Yarotskyy Keith S. Elmslie 《Biophysical journal》2010,98(7):1149-1159
Ca2+ entry through L-type calcium channels (CaV1.2) is critical in shaping the cardiac action potential and initiating cardiac contraction. Modulation of CaV1.2 channel gating directly affects myocyte excitability and cardiac function. We have found that phospholemman (PLM), a member of the FXYD family and regulator of cardiac ion transport, coimmunoprecipitates with CaV1.2 channels from guinea pig myocytes, which suggests PLM is an endogenous modulator. Cotransfection of PLM in HEK293 cells slowed CaV1.2 current activation at voltages near the threshold for activation, slowed deactivation after long and strong depolarizing steps, enhanced the rate and magnitude of voltage-dependent inactivation (VDI), and slowed recovery from inactivation. However, Ca2+-dependent inactivation was not affected. Consistent with slower channel closing, PLM significantly increased Ca2+ influx via CaV1.2 channels during the repolarization phase of a human cardiac action potential waveform. Our results support PLM as an endogenous regulator of CaV1.2 channel gating. The enhanced VDI induced by PLM may help protect the heart under conditions such as ischemia or tachycardia where the channels are depolarized for prolonged periods of time and could induce Ca2+ overload. The time and voltage-dependent slowed deactivation could represent a gating shift that helps maintain Ca2+ influx during the cardiac action potential waveform plateau phase. 相似文献
998.
Viktor I. Korolchuk 《FEBS letters》2010,584(7):1393-1398
The ubiquitin proteasome system (UPS) and macroautophagy (hereafter called autophagy) were, for a long time, regarded as independent degradative pathways with few or no points of interaction. This view started to change recently, in the light of findings that have suggested that ubiquitylation can target substrates for degradation via both pathways. Moreover, perturbations in the flux through either pathway have been reported to affect the activity of the other system, and a number of mechanisms have been proposed to rationalise the link between the UPS and autophagy. Here we critically review these findings and outline some outstanding issues that still await clarification. 相似文献
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