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121.
A non-adiabatic theory of Electron Transfer (ET), which improves the standard theory near the inversion point and becomes equivalent to it far from the inversion point, is presented. The complex amplitudes of the electronic wavefunctions at different sites are used as Kramers variables for describing the quantum tunneling of the electron in the deformable potential generated by its environment (nonadiabaticity) which is modeled as a harmonic classical thermal bath. After exact elimination of the bath, the effective electron dynamics is described by a discrete nonlinear Schrödinger equation with norm preserving dissipative terms and a Langevin random force, with a frequency cut-off, due to the thermalized phonons. This theory reveals the existence of a specially interesting marginal case when the linear and nonlinear coefficients of a two electronic states system are appropriately tuned for forming a Coherent Electron-Phonon Oscillator (CEPO). An electron injected on one of the electronic states of a CEPO generates large amplitude charge oscillations (even at zero temperature) associated with coherent phonon oscillations and electronic level oscillations. This fluctuating electronic level may resonate with a third site which captures the electron so that Ultrafast Electron Transfer (UFET) becomes possible. Numerical results are shown where two weakly interacting sites, a donor and a catalyst, form a CEPO that triggers an UFET to an acceptor. Without a catalytic site, a very large energy barrier prevents any direct ET. This UFET is shown to have many qualitative features similar to those observed in the primary charge separation in photosynthetic reaction centers. We suggest that more generally, CEPO could be a paradigm for understanding many selective chemical reactions involving electron transfer in biosystems. 相似文献
122.
Chalevelakis G Apostolakis I Koliou X Apessos A Kyriakopoulou V Vrakidou E Vasilopoulou A Lamnisou K Nasioulas G 《Genetic testing》2008,12(1):125-127
Familial Mediterranean fever (FMF) is a heterogeneous disorder; at present, it is diagnosed using only genetic methods. In the current study, we performed molecular analysis in two families presenting with FMF. In the first family, we report two brothers with a common genotype (M694V/V726A) but with different clinical presentation. In the second family, we identified the M694V and K695R mutations in a presymptomatic carrier. 相似文献
123.
gp130 is a shared receptor for at least nine cytokines and can signal either as a homodimer or as a heterodimer with Leukemia Inhibitory Factor Receptor (LIF-R). Here, we biophysically and structurally characterize the full-length, transmembrane form of a quaternary cytokine receptor complex consisting of gp130, LIF-R, the cytokine Ciliary Neurotrophic Factor (CNTF), and its alpha receptor (CNTF-Ralpha). Thermodynamic analysis indicates that, unlike the cooperative assembly of the symmetric gp130/Interleukin-6/IL-6Ralpha hexameric complex, CNTF/CNTF-Ralpha heterodimerizes gp130 and LIF-R via noncooperative energetics to form an asymmetric 1:1:1:1 complex. Single particle electron microscopic analysis of the full-length gp130/LIF-R/CNTF-Ralpha/CNTF quaternary complex elucidates an asymmetric structural arrangement, in which the receptor extracellular and transmembrane segments join as a continuous, rigid unit, poised to sensitively transduce ligand engagement to the membrane-proximal intracellular signaling regions. These studies also enumerate the organizing principles for assembly of the "tall" class of gp130 family cytokine receptor complexes including LIF, IL-27, IL-12, and others. 相似文献
124.
Pavlos Konstantinidis Georgios Tsiourlis Panteleimon Xofis G. Peter Buckley 《Plant Ecology》2008,195(2):235-256
Castanea sativa Mill. is an important species of the Balkan Peninsula with high ecological and economic value. This article contributes to
a phytosociological synsystematic approach of the C. sativa plant communities in Greece that covers the southern part of the Balkan Peninsula and describes the ecological parameters
involved in their distribution and taxonomy. Phytosociological data have been collected from 14 mountainous areas across continental
Greece, which are considered representative of the main forest types of C. sativa in the area. The 14 mountains demonstrate a variety of environmental conditions. Five communities (associations) and seven
sub-communities (sub-associations) have been identified and described using TWINSPAN, Corespondence Analysis and the Braun-Blanquet
classification scheme.
Castanea sativa (chestnut) forests of Greece can be distinguished as three broad groups, defined primarily by their geographical distribution.
In northern and central Greece chestnut stands are characterized by their high floristic homogeneity, which is reflected in
the identification of only one community per region. Chestnut forests in northern Greece, in particular, exhibit strong floristic
similarities with those of the rest of the Balkans. In southern Greece, on the other hand, the southern distribution limit
of chestnut in the Balkans, there is a greater floristic diversity between the sampled mountains which is reflected in the
presence of three confirmed communities and two sub-associations.
Several factors have been identified as important in determining the structure and floristic composition of chestnut forests
in Greece. Whilst climate and the grazing regime are influential, the degree of silvicultural management appears to be the
most important factor determining the floristic composition of chestnut forests and their long-term sustainability. 相似文献
125.
Link AJ Skretas G Strauch EM Chari NS Georgiou G 《Protein science : a publication of the Protein Society》2008,17(10):1857-1863
G protein-coupled receptors (GPCRs) are notoriously difficult to express, particularly in microbial systems. Using GPCR fusions with the green fluorescent protein (GFP), we conducted studies to identify bacterial host effector genes that result in a general and significant enhancement in the amount of membrane-integrated human GPCRs that can be produced in Escherichia coli. We show that coexpression of the membrane-bound AAA+ protease FtsH greatly enhances the expression yield of four different class I GPCRs, irrespective of the presence of GFP. Using this new expression system, we produced 0.5 and 2 mg/L of detergent-solubilized and purified full-length central cannabinoid receptor (CB1) and bradykinin receptor 2 (BR2) in shake flask cultures, respectively, two proteins that had previously eluded expression in microbial systems. 相似文献
126.
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128.
Phanourios Tamamis Meital Reches Pawel Sikorski Ehud Gazit Georgios Archontis 《Biophysical journal》2009,96(12):5020-5029
Studies of peptide-based nanostructures provide general insights into biomolecular self-assembly and can lead material engineering toward technological applications. The diphenylalanine peptide (FF) self-assembles into discrete, hollow, well ordered nanotubes, and its derivatives form nanoassemblies of various morphologies. Here we demonstrate for the first time, to our knowledge, the formation of planar nanostructures with β-sheet content by the triphenylalanine peptide (FFF). We characterize these structures using various microscopy and spectroscopy techniques. We also obtain insights into the interactions and structural properties of the FF and FFF nanostructures by 0.4-μs, implicit-solvent, replica-exchange, molecular-dynamics simulations of aqueous FF and FFF solutions. In the simulations the peptides form aggregates, which often contain open or ring-like peptide networks, as well as elementary and network-containing structures with β-sheet characteristics. The networks are stabilized by polar and nonpolar interactions, and by the surrounding aggregate. In particular, the charged termini of neighbor peptides are involved in hydrogen-bonding interactions and their aromatic side chains form “T-shaped” contacts, as in three-dimensional FF crystals. These interactions may assist the FF and FFF self-assembly at the early stage, and may also stabilize the mature nanostructures. The FFF peptides have higher network propensities and increased aggregate stabilities with respect to FF, which can be interpreted energetically. 相似文献
129.
Multiple cellular pathways have been shown to be involved during fiber initiation and elongation stages in the cultivated allotetraploid cotton (Gossypium hirsutum). The cell wall enzymes xyloglucan endotransglycosylase/hydrolases (XTH) have been reported to be associated with the biosynthesis of the cell wall and the growth of cotton fibers, probably regulating the plasticity of the primary cell wall. Among various cotton fiber cDNAs found to be preferentially expressed in cotton fibers, a xyloglucan endotransglycosylase (XTH) cDNA was significantly up-regulated during the elongation stage of cotton fiber development. In the present study, we isolated and characterized genomic clones encoding cotton XTH from cultivated cotton (Gossypium hirsutum) and its diploid progenitors (Gossypium arboreum and Gossypium raimondii), designated GhXTH1-1, GhXTH1-2, GaXTH1 and GrXTH, respectively. In addition, we isolated and characterized, by in silico methods, the putative promoter of XTH1 from Gossypium hirsutum. Sequence analysis revealed more than 50% homology to XTH's at the protein level. DNA gel blot hybridization indicated that at least two copies of GhXTH1 are present in Gossypium hirsutum whereas the diploid progenitor species Gossypium arboreum and Gossypium raimondii has only a single copy. Quantitative real-time PCR and high-resolution melting experiments indicated that in Gossypium hirsutum cultivars, in cotton fibers during early stages of fiber elongation specifically expressing only the GhXTH1-1 gene and expression levels of GhXTH1-1 in fibers varies among cultivars differing in fiber percentage and fiber length. 相似文献
130.