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1.
B. Spagnolo S. Spezia L. Curcio N. Pizzolato A. Fiasconaro D. Valenti P. Lo Bue E. Peri S. Colazza 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):133-146
We investigate the role of the colored noise in two
biological systems: (i) adults of Nezara viridula (L.)
(Heteroptera: Pentatomidae), and (ii) polymer translocation. In the
first system we analyze, by directionality tests, the response of
N. viridula individuals to subthreshold signals plus noise
in their mating behaviour. The percentage of insects that react to
the subthreshold signal shows a nonmonotonic behaviour,
characterized by the presence of a maximum, as a function of the
noise intensity. This is the signature of the non-dynamical
stochastic resonance phenomenon. By using a “soft” threshold model
we find that the maximum of the input-output cross correlation
occurs in the same range of noise intensity values for which the
behavioural activation of the insects has a maximum. Moreover this
maximum value is lowered and shifted towards higher noise
intensities, compared to the case of white noise. In the second
biological system the noise driven translocation of short polymers
in crowded solutions is analyzed. An improved version of the Rouse
model for a flexible polymer is adopted to mimic the molecular
dynamics by taking into account both the interactions between
adjacent monomers and the effects of a Lennard-Jones potential
between all beads. The polymer dynamics is simulated in a
two-dimensional domain by numerically solving the Langevin equations
of motion in the presence of thermal fluctuations and a colored
noise source. At low temperatures or for strong colored noise
intensities the translocation process of the polymer chain is
delayed. At low noise intensity, as the polymer length increases, we
find a nonmonotonic behaviour for the mean first translocation time
of the polymer centre of inertia. We show how colored noise
influences the motion of short polymers, by inducing two different
regimes of translocation in the dynamics of molecule transport. 相似文献
2.
Giahi A El Alaoui Faris M Bassereau P Salditt T 《The European physical journal. E, Soft matter》2007,23(4):431-437
In view of recent theories of “active” membranes, we have studied multilamellar phospholipid membrane stacks with reconstituted
transmembrane protein bacteriorhodopsin (BR) under different illumination conditions by X-ray scattering. The light-active
protein is considered as an active constituent which drives the system out of equilibrium and is predicted to change the collective
fluctuation properties of the membranes. Using X-ray reflectivity, X-ray non-specular (diffuse) scattering, and grazing incidence
scattering, we find no detectable change in the scattering curves when changing the illumination condition. In particular
the intermembrane spacing d remains constant, after eliminating hydration-related artifacts by design of a suitable sample environment. The absence of
any observable non-equilibrium effects in the experimental window is discussed in view of the relevant parameters and recent
theories. 相似文献
3.
S. Mangenot E. Raspaud C. Tribet L. Belloni F. Livolant 《The European physical journal. E, Soft matter》2002,7(3):221-231
Interactions between isolated nucleosome core particles are studied as a function of the monovalent salt concentration by
osmometry and by electrophoretic mobility measurements. The data are compared to the measurements performed on the protein-free
DNA fragments and also analysed using the conventional theoretical approach. At low salt, an electrostatic screening effect
accounts for the variation of the second virial coefficient whereas the simple hard-core contribution becomes predominant
at high salt. In the intermediate range, an attraction occurs. In the light of previous results (Mangenot et al. Biophys. J. 82, 345 (2002)), we show that the flexible basic proteic tails are responsible for this attraction. A tail-bridging effect is
discussed.
Received 4 October 2001 相似文献
4.
We consider surfaces with disordered charge distribution. The disorder can be caused by mobile charges, as for example in
mixed lipid bilayers, or by weakly charged surfaces where charge regulation takes place (e.g. carboxyl groups). Using Monte-Carlo
simulation methods we find for quenched as well as annealed disordered charge distributions counterion densities close to
the surface that are significantly larger than for ordered regularly spaced surface ions. Our field-theoretic results agree
well with results obtained from Monte-Carlo simulations of the system. Furthermore, we obtain expressions for the effective
interaction between charged colloids and charged rods close to a charged surface and discuss the effect of the surface-ion
mobility and polarization charges on the interaction. In general, polarization effects as well as surface-ion mobility lead
to a weakening of the effective interaction between charged objects. 相似文献
5.
C.W. Maier A. Behrisch A. Kloboucek D.A. Simson R. Merkel 《The European physical journal. E, Soft matter》2001,6(4):273-276
We studied biomembrane adhesion using the micropipet aspiration technique. Adhesion was caused by contact site A, a laterally
mobile and highly specific cell adhesion molecule from Dictyostelium discoideum, reconstituted in lipid vesicles of DOPC (L-α-dioleoylphosphatidylcholine) with an addition of 5 mol % DOPE-PEG2000 (1,2-diacyl-sn-glycero-3-phosphatidylethanolamine-N-[poly(ethyleneglycol) 2000]). The “fuzzy” membrane mimics the cellular
plasma membrane including the glycocalyx. We found adhesion and subsequent receptor migration into the contact zone. Using
membrane tension jumps to probe the equation of state of the two-dimensional “gas” of bound receptor pairs within the contact
zone, we found strong, attractive lateral interactions.
Received 16 February 2001 相似文献
6.
F. Pincet S. Cribier E. Perez 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):127-130
Many experiments done on neutral lipid bilayers in pure water show weak repulsions. These weak forces prevent vesicles from
adhering and are generally overcome by adding some salt in the aqueous medium. They also appear as stray repulsions in surface
forces measurements made on lipid bilayers. Using a surface forces apparatus in pure water and in salt solution, we have measured
the forces between two stearoyl-oleoyl-phosphatidyl-choline (SOPC) bilayers and between two dimiristoyl-phosphatidyl-ethanolamine
(DMPE) bilayers. The results show that the repulsions are due to a small amount of negative charges coming from impurities
in SOPC. This was quantitatively confirmed by electrophoretic measurements. There are 3 times less charges in the case of
DMPE layers. The effect of these charges which is negligible at high salt concentration may significantly affect the adhesion
energy and behaviour of neutral lipid bilayers between 0 and salt.
Received 18 December 1998 相似文献
7.
P.G. Dommersnes J.-B. Fournier 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):9-12
We study the collective behavior of inclusions inducing local anisotropic curvatures in a flexible fluid membrane. The N-body interaction energy for general anisotropic inclusions is calculated explicitly, including multi-body interactions. Long-range
attractive interactions between inclusions are found to be sufficiently strong to induce aggregation. Monte Carlo simulations
show a transition from compact clusters to aggregation on lines or circles. These results might be relevant to proteins in
biological membranes or colloidal particles bound to surfactant membranes.
Received 30 July 1999 and Received in final form 8 September 1999 相似文献
8.
α-突触核蛋白(α-synuclein,α-syn)在帕金森病的发病机理中起着关键的作用,因而近年来受到了越来越广泛的关注.α-syn在膜上的动力学过程对理解其功能至关重要.本文使用基于脂质体的单分子荧光衰减方法——LipoFRET,首次对较高浓度下α-syn与磷脂膜的相互作用的动态过程进行了单分子层面上的研究.研究发现,在溶液中α-syn浓度升高时,其中央NAC区域可离开磷脂膜表面进入水相中;而N端部分位于膜表面内的位置变浅,并有更高的概率脱离膜表面进入溶液中.利用单分子荧光成像对α-syn解离的观察则发现,随着溶液中的α-syn浓度升高,脂质体上的α-syn解离速率加快.因此高浓度下,α-syn在膜上各区域垂直位置变化促进了蛋白从膜上的解离.结合LipoFRET的实验结果可以推断,α-syn的解离可能是由于不同的α-syn分子膜作用位点互相竞争而导致的解离.这样的特征,可能是体内环境中影响α-syn控制其聚集的重要性质. 相似文献
9.
V.S. Shelkovsky S.G. Stepanian I.K. Galetich M.V. Kosevich L. Adamowicz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):421-430
A combined experimental-theoretical approach to modeling of building blocks of recognition complexes formed by nucleic acid
bases and the amino-acids side-chain amino group is reviewed. The approach includes the temperature dependent field-ionization
mass spectrometry and ab initio quantum chemical calculations. The mass spectrometric technique allows determination of interaction enthalpies of biomolecules
in the gas phase, and the results it produces are directly comparable to the results obtained through theoretical modeling.
In our works we have analyzed both thermodynamic and structural aspects of the recognition complexes of four canonical nucleic
acid bases and acrylamide, which models the side chain of asparagine and glutamine. It has been shown that all bases can interact
with amide group of the amino acids via their Watson-Crick sites when being incorporated into a single strand DNA or RNA. Stability of the complexes studied, expressed
as - ΔH (kJ mole-1) decreases as: m9Gua (- 59.5) > m
1Cyt (- 57.0) > m
9Ade (- 52.0) ≫m
1Ura (- 40.6). We have determined that in the double stranded DNA only purine bases can be recognized.
Received 5 February 2002 and Received in final form 14 March 2002 Published online 13 September 2002 相似文献
10.
Research on protein–membrane interactions has been undeveloped due to the lack of proper techniques to detect the position of proteins at membranes because membranes are usually only about 4-nm thick. We have recently developed a new method named surface-induced fluorescence attenuation(SIFA) to track both vertical and lateral kinetics of a single labelling dye in supported lipid bilayers. It takes advantage of strong interaction between a light-emitting dye and a partially reflecting surface. By applying the technique to membrane proteins being fluorescently labelled at different residues, here we show that SIFA can measure not only the insertion depth of a dye inside a lipid bilayer, but also the position of a dye in solution near the surface. SIFA can therefore be used to study membrane proteins of various types. 相似文献