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51.
von Stetten D Seibeck S Michael N Scheerer P Mroginski MA Murgida DH Krauss N Heyn MP Hildebrandt P Borucki B Lamparter T 《The Journal of biological chemistry》2007,282(3):2116-2123
The mutants H250A and D197A of Agp1 phytochrome from Agrobacterium tumefaciens were prepared and investigated by different spectroscopic and biochemical methods. Asp-197 and His-250 are highly conserved amino acids and are part of the hydrogen-bonding network that involves the chromophore. Both substitutions cause a destabilization of the protonated chromophore in the Pr state as revealed by resonance Raman and UV-visible absorption spectroscopy. Titration experiments demonstrate a lowering of the pK(a) from 11.1 (wild type) to 8.8 in H250A and 7.2 in D197A. Photoconversion of the mutants does not lead to the Pfr state. H250A is arrested in a meta-Rc-like state in which the chromophore is deprotonated. For H250A and the wild-type protein, deprotonation of the chromophore in meta-Rc is coupled to the release of a proton to the external medium, whereas the subsequent proton re-uptake, linked to the formation of the Pfr state in the wild-type protein, is not observed for H250A. No transient proton exchange with the external medium occurs in D197A, suggesting that Asp-197 may be the proton release group. Both mutants do not undergo the photo-induced protein structural changes that in the wild-type protein are detectable by size exclusion chromatography. These conformational changes are, therefore, attributed to the meta-Rc --> Pfr transition and most likely coupled to the transient proton re-uptake. The present results demonstrate that Asp-197 and His-250 are essential for stabilizing the protonated chromophore structure in the parent Pr state, which is required for the primary photochemical process, and for the complete photo-induced conversion to the Pfr state. 相似文献
52.
Reti NG Lappas M Huppertz B Riley C Wlodek ME Henschke P Permezel M Rice GE 《Cell and tissue research》2007,328(3):607-616
Ex situ culture of human gestational tissues has been routinely used as a model to investigate tissue function. The objective of
this study was to determine the effect of varying oxygen concentrations on human term placental explants over a 24-h time
period. Specifically, the effect of incubating placental explants in oxygen concentrations of 8%, 21% or 95% on tissue viability,
metabolism and cell death was measured by assessing glucose consumption, lactate production, release of lactate dehydrogenase,
parathyroid hormone-related protein (PTHrP), tumour necrosis factor-alpha (TNF-α) and 8-isoprostane, immunoreactivity for
cleaved-caspase-9 and immunohistochemistry for the caspase-3-cleaved cytokeratin-18 neoepitope, M30. Exposure to higher oxygen
concentrations significantly increased the rates of glucose consumption and lactate production. Apoptosis was significantly
increased under conditions of higher oxygen as evidenced by increased M30 in placental explant sections. Similarly, hyperoxia
significantly increased the releases of PTHrP, TNF-α and 8-isoprostane. Thus, incubation of placental explants with oxygen
concentrations of 95% and, to a lesser extent, 21% oxygen was associated with the modulation of multiple cellular response
pathways including those associated with tissue viability and cell death. These data are consistent with the hypothesis that
hyperoxia activates pathways and mechanisms involved in cellular metabolism, necrosis and apoptosis, thereby shifting the
balance from a steady state towards cell death. 相似文献
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54.
The aromatic thioether (2,6-bis((2-(dimethylamino)ethylamino)methyl)phenyl)(tert-butyl)sulfane (6) reacts with [Pd(NCCH3)2Cl2] under S-C bond cleavage to give the dinuclear palladium(II) complex [L3Pd2(μ-Cl)]2+ (7), where (L3)− = 2,6-bis((2-(dimethylamino)ethylamino)methyl)-thiophenolate. Complex 7 reacts readily with sodium acetate and sodium acetamide by the displacement of the bridging chloride group forming [L3Pd2(μ-OAc)]2+ (8) and [L3Pd2(μ-ONHCCH3)]2+ (9), respectively. Complex 8 can also be prepared by the reaction of 6 with [Pd(OAc)2]. All complexes were isolated as perchlorate salts and fully characterized by ESI-MS, IR, 1H, and 13C NMR spectroscopy. The structures of 7[ClO4] and 9[ClO4]2 have been determined by X-ray crystallography. The latter structure reveals a μ1,3-bridging acetamidate unit showing that (L3)− can alter its conformation sufficiently to accommodate a multi-atom bridging species between the two Pd atoms. 相似文献
55.
Iron-uptake is well studied in a plethora of pro- and eukaryotic organisms with the exception of Archaea, which thrive mainly
in extreme environments. In this study, the mechanism of iron transport in the extremely halophilic Euryarchaeon Halobacterium salinarum strain JW 5 was analyzed. Under low-iron growth conditions no siderophores were detectable in culture supernatants. However,
various xenosiderophores support growth of H. salinarum. In [55Fe]–[14C] double-label experiments, H. salinarum displays uptake of iron but not of the chelator citrate. Uptake of iron was inhibited by cyanide and at higher concentrations
by Ga. Furthermore, a KM for iron uptake in cells of 2.36 μM and a Vmax of approximately 67 pmol Fe/min/mg protein was determined. [55Fe]-uptake kinetics were measured in the absence and presence of Ga. Uptake of iron was inhibited merely at very high Ga concentrations.
The results indicate an energy dependent iron uptake process in H. salinarum and suggest reduction of the metal at the membrane level. 相似文献
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59.
Prunotto M Ghiggeri G Bruschi M Gabbiani G Lescuyer P Hocher B Chaykovska L Berrera M Moll S 《Journal of Proteomics》2011,74(10):1855-1870
Renal tubulo-interstitial fibrosis is a non-specific process, representing the final common pathway for all kidney diseases, irrespective of their initial cause, histological injury, or etiology, leading to gradual expansion of the fibrotic mass which destroys the normal structure of the tissue and results in organ dysfunction and, ultimately, in end-stage organ failure. Proteomic studies of the fibrotic pathophysiological mechanisms have been performed in cell cultures, animal models and human tissues, addressing some of the key issues. This article will review proteomic contribution to the raising current knowledge on renal fibrosis biology and also mention seminal open questions to which proteomic techniques and proteomists could fruitfully contribute. 相似文献
60.