bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational wave functions and spectroscopy of (H2O)n, n=2,3,4,5: Vibrational self-consistent field with correlation corrections
Authors: Jung Joon O. , Gerber R. Benny
Published: July 2002

Vibrational energy levels, wave functions, and ir absorption intensities are computed for (H2O)n clusters with n=2, 3, 4, and 5. The calculations were carried out by the vibrational self-consistent field (VSCF) approximation, with corrections for correlations between the modes by perturbation theory. This correlation corrected VSCF (CC-VSCF) is analogous to the familiar Möller–Plesset method in electronic structure theory. Test calculations indicate that this method is of very good accuracy also for very anharmonic systems. While the method is of highest relative accuracy for the stiffest modes, it works very well also for the soft ones. Some of the main results are (1) the frequencies calculated are in good but incomplete agreement with experimental data available for some of the intramolecular mode excitations. The deviations are attributed to the inaccuracy of the coupling between intramolecular and intermolecular modes for the potential function used. (2) Insight is gained into the pattern of blue- or redshifts from the corresponding harmonic excitation energies for the various modes. (3) Anharmonic coupling between the modes dominates in general over the intrinsic anharmonicity of individual modes in determining the spectrum. (4) The anharmonic corrections to the frequencies of some intermolecular modes (shearing, torsional) are extremely large, and exceed 100% or more in many cases. (5) An approximation of quartic potential field in the normal mode displacement is tested for the clusters. It works well for the high and intermediate frequency modes, but is in error for very soft shearing and torsional modes. (6) The relative errors of the VSCF approximation are found to decrease with the cluster size. This is extremely encouraging for calculations of large clusters, since the VSCF level is computationally simple.
Small-angle x-ray scattering analysis of polymer-protected platinum, rhodium, and platinum/rhodium colloidal dispersions
Authors: Hashimoto Takeji , Saijo Kenji , Harada Masafumi , Toshima Naoki
Published: July 2002

Formations of poly(N-vinyl-2-pyrrolidone)(PVP)-metal ion (Pt, Rh or Pt/Rh(1/1)) complexes in H2O/C2H5OH (“polymer–metal ion complexes”) before alcohol-reduction and PVP–Pt, Rh, or Pt/Rh(1/1) metal cluster (“polymer–metal cluster”) after alcohol-reduction were studied by small-angle x-ray scattering (SAXS). SAXS intensity of the solution containing polymer–metal ion complexes is higher than that of the reference polymer solution without metal ions, suggesting that concentration fluctuations of polymer segments are enhanced due to the formation of polymer–metal ion complexes. Spatial distributions of metal clusters in colloidal dispersions are different from each other among the cases of Pt, Rh, and Pt/Rh(1/1) colloidal dispersions. The superstructure (greater than 10.0 nm in diameter), whose average sizes highly depend on the metal element employed, are formed. These superstructures are composed of several fundamental clusters with a diameter of ∼2.0–4.0 nm. Colloidal dispersions of Rh form a percolation network of clusters with an average period of ∼6.0 nm inside the higher-order organization of its superstructure. Experimental results concerning the physical aging show the high stability of colloidal dispersions of metal clusters protected by water-soluble PVP.
A biased Monte Carlo scheme for zeolite structure solution
Authors: Falcioni Marco , Deem Michael W.
Published: July 2002

We describe a new, biased Monte Carlo scheme to determine the crystal structures of zeolites from powder diffraction data. We test the method on all publicly known zeolite materials, with success in all cases. We show that the method of parallel tempering is a powerful supplement to the biased Monte Carlo.
Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy
Authors: Hollars Christopher W. , Dunn Robert C.
Published: July 2002

Single molecule near-field fluorescence measurements are utilized to characterize the molecular level structure in Langmuir–Blodgett monolayers of L-α-dipalmitoylphosphatidylcholine (DPPC). Monolayers incorporating 3×10−4 mol % of the fluorescent lipid analog N-(6-tetramethylrhodaminethiocarbamoyl)-1,2-dihexadecanoyl-sn- glycero-3-phosphoethanolamine, triethylammonium salt (TRITC–DHPE) are transferred onto a freshly cleaved mica surface at low (π=8 mN/m) and high (π=30 mN/m) surface pressures. The near-field fluorescence images exhibit shapes in the single molecule images that are indicative of the lipid analog probe orientation within the films. Modeling the fluorescence patterns yields the single molecule tilt angle distribution in the monolayers which indicates that the majority of the molecules are aligned with their absorption dipole moment pointed approximately normal to the membrane plane. Histograms of the data indicate that the average orientation of the absorption dipole moment is 2.2° (σ=4.8°) in monolayers transferred at π=8 mN/m and 2.4° (σ=5.0°) for monolayers transferred at π=30 mN/m. There is no statistical difference in the mean tilt angle or distribution for the two monolayer conditions studied. The insensitivity of tilt angle to film surface pressure may arise from small chromophore doped domains of trapped liquid-expanded lipid phase remaining at high surface pressure. There is no evidence in the near-field fluorescence images for probe molecules oriented with their dipole moment aligned parallel with the membrane plane. We do, however, find a small but significant population of probe molecules (∼13%) with tilt angles greater than 16°. Comparison of the simultaneously collected near-field fluorescence and force images suggests that these large angle orientations are not the result of significant defects in the films. Instead, this small population may represent a secondary insertion geometry for the probe molecule into the lipid monolayer.
On non-negativity of Fukui function indices. II
Authors: Kinkar Roy Ram , Hirao Kimihiko , Pal Sourav
Published: July 2002

In this article we have tried to critically analyze the factors which cause the condensed Fukui function (FF) indices [f(r)] to attain a negative value in some cases. The evaluation of condensed FF indices needs finite-difference approximation to the electronic charge densities, and the finite-difference approximation needs partitioning of the electronic charge to the constituent atoms. In a previous article [J. Chem. Phys. 110, 8236 (1999)] we have argued that the probable factors, which cause the FF indices to appear negative in some cases, may be (i) the improper charge partitioning techniques adopted to evaluate f(r); (ii) large change in the electron number (ΔN=1) when f(r) is evaluated in condensed form using the finite-difference approximation. In this article we want to focus more on the first factor. The present study shows through pictorial as well as numerical demonstrations of the charge-density difference [ρneutral(r̄)−ρcation(r̄) and ρanion(r̄)−ρneutral(r̄)] plots, how the negative condensed FF value appears with the use of improper charge partitioning and how the use of Hirshfeld partitioning can solve this problem.
The Kadomtsev–Petviashvili equation as a source of integrable model equations
Authors: Maccari Attilio
Published: July 2002

A new integrable and nonlinear partial differential equation (PDE) in 2+1 dimensions is obtained, by an asymptotically exact reduction method based on Fourier expansion and spatiotemporal rescaling, from the Kadomtsev–Petviashvili equation. The integrability property is explicitly demonstrated, by exhibiting the corresponding Lax pair, that is obtained by applying the reduction technique to the Lax pair of the Kadomtsev–Petviashvili equation. This model equation is likely to be of applicative relevance, because it may be considered a consistent approximation of a large class of nonlinear evolution PDEs.
Nonrelativistic conformal groups
Authors: Negro J. , del Olmo M. A. , Rodrı́guez-Marco A.
Published: July 2002

In this work a systematic study of finite-dimensional nonrelativistic conformal groups is carried out under two complementary points of view. First, the conformal Killing equation is solved to obtain a whole family of finite-dimensional conformal algebras corresponding to each of the Galilei and Newton–Hooke kinematical groups. Some of their algebraic and geometrical properties are studied in a second step. Among the groups included in these families one can identify, for example, the contraction of the Minkowski conformal group, the analog for a nonrelativistic de Sitter space, or the nonextended Schrödinger group.
Geodesics in Lewis space–time
Authors: Herrera L. , Santos N. O.
Published: July 2002

The geodesic equations are integrated for the Lewis metric and the effects of the different parameters appearing in the Weyl class on the motion of test particles are brought out. The appearance of a force parallel to the axial axis is without Newtonian analog and deserves particular attention.
An algebraic model for nonisotropic turbulent dissipation rate in Reynolds stress closures
Authors: Hallbäck Magnus , Groth Johan , Johansson Arne V.
Published: July 2002

A method to account for effects of an anisotropic dissipation rate in second-order moment closures of turbulent flows is presented. The modeled transport equations for the Reynolds stresses and the scalar dissipation rate are supplemented by nonlinear algebraic relations, in which the anisotropies of the dissipation rate tensor are expressed in the anisotropies of the Reynolds stress tensor. Symmetry and other constraints reduce the number of undetermined coefficients to one. It is shown that the model correctly describes the initial behavior of a suddenly distorted turbulence provided that the model parameter assumes a value of (3)/(4) . The model is compared with full numerical simulations of three basic types of strained homogeneous turbulence, and is shown to give good agreement with these data. The present approach of isolating the effects of anisotropic dissipation rate in second-order moment closures is a step toward improved modeling of the energy redistribution terms in the Reynolds stress transport equations, and could also be used for improved modeling of the scalar dissipation rate equation.
Double layers, spiky solitary waves, and explosive modes of relativistic ion-acoustic waves propagating in a plasma
Authors: Nejoh Yasunori
Published: July 2002

The fully relativistic ion fluid equations are presented. These equations are reduced to a mixed modified Korteweg–de Vries (MKdV) equation by using the reductive perturbation method. The high-speed streaming ions and the negative cubic nonlinearity of the mixed MKdV equation give rise to the new nonlinear wave modes, that is, the compressive double layer, the spiky solitary wave, and the explosive solutions. The double layer and the spiky solitary wave are confined within the specified positive potential region, while the explosive solutions are confined within the region where the potential exceeds the maximum potential or the negative potential region. It is shown for the first time that the double-layer thickness narrows as the ion temperature and the relativistic effects increase, that the potential drop of the double layer grows as the ion temperature increases, and that the amplitudes of the spiky solitary wave and the explosive solution grow as the ion temperature effect increases. This investigation relates to the evolution process of the nonlinear wave structure in which these three modes form the fine structure in space.
Experiments on convection at very high Rayleigh numbers
Authors: Foster Theodore D. , Waller Steven
Published: July 2002

Experiments in which a thick layer of fluid was heated from below at a constant rate were conducted at flux Rayleigh numbers in the range of 109 to 1012. The resulting convection was investigated by statistical analysis of the temperature signals from a pair of thermistor probes at different horizontal spacings. Power spectra showed that the temperature variance was distributed over a broad band of periods but that the centroid of this band, the characteristic period, depended very nearly on the − (1)/(2) power of the heat flux. Measurements of the coherency between the probe signals at varying distances were interpreted as defining a characteristic horizontal length scale that depended approximately upon the − (1)/(4) power of the heat flux. These results tend to substantiate the boundary layer instability model of convection at very high Rayleigh numbers.
Fingering with miscible fluids in a Hele Shaw cell
Authors: Paterson Lincoln
Published: July 2002

Unstable, two-fluid miscible displacements in a Hele Shaw cell of plate spacing b are analyzed by considering viscous dissipation of energy. A perturbation theory is presented that predicts the wavelength of fingers, λ, as λ≊4b. Experiments with a circular Hele Shaw cell are shown to support this result. In a porous medium, the analogous fingers are demonstrated to be the size of a pore, which is much larger than the corresponding fingers in the analogous Hele Shaw cell. These results provide the lower limits of finger wavelength for the theories of Saffman and Taylor, and Chuoke, van Meurs, and van der Poel.
An investigation of large-scale structure in the similarity region of a two-dimensional turbulent jet
Authors: Thomas F. O. , Brehob E. G.
Published: July 2002

An experimental investigation of large-scale structural patterns in the similarity region of a two-dimensional turbulent jet was performed. Two-point correlation and coherence-based measurements obtained from both longitudinal and lateral component velocity fluctuations are, in general, supportive of the existence of an antisymmetric array of counterrotating vortices in the similarity region. Particularly graphic evidence is obtained from detailed isocorrelation contour maps that are presented. A novel method of determining structural convective velocity is developed and indicates the structural array propagates at 60% of the local centerline mean velocity. Very limited structural two dimensionality is exhibited in the direction of mean flow homogeneity and it is suggested that this is likely to be related to the existence of multiple coherent modes in the flow.
The dynamic Smagorinsky model and scale-dependent coefficients in the viscous range of turbulence
Authors: Meneveau Charles , Lund Thomas S.
Published: July 2002

The standard dynamic procedure is based on the scale-invariance assumption that the model coefficient C is the same at the grid and test-filter levels. In many applications this condition is not met. We consider the case when the filter-length, Δ, approaches the Kolmogorov scale, η, and C(Δ→η)→0̇. Using filtered direct numerical simulation data, we show that the standard dynamic model yields the coefficient corresponding to the test-filter scale (αΔ) instead of the grid scale (Δ). Several approaches to account for scale dependence in the dynamic Smagorinsky model are considered, and the most robust of these is tested in large eddy simulation of forced isotropic turbulence at various Reynolds numbers.
Electrostatic atomization—Experiment, theory and industrial applications
Authors: Okuda H. , Kelly Arnold J.
Published: July 2002

Experimental and theoretical research has been initiated at the Princeton Plasma Physics Laboratory on the electrostatic atomization process in collaboration with Charged Injection Corporation. The goal of this collaboration is to set up a comprehensive research and development program on the electrostatic atomization at the Princeton Plasma Physics Laboratory so that both institutions can benefit from the collaboration. Experimental, theoretical and numerical simulation approaches are used for this purpose. An experiment consisting of a capillary sprayer combined with a quadrupole mass filter and a charge detector was installed at the Electrostatic Atomization Laboratory to study fundamental properties of the charged droplets such as the distribution of charges with respect to the droplet radius. In addition, a numerical simulation model is used to study interaction of beam electrons with atmospheric pressure water vapor, supporting an effort to develop an electrostatic water mist fire-fighting nozzle.
Static model for dusts in a plasma
Authors: Chen Yan-Ping , Luo Huaqiang , Ye Mao-Fu , Yu M. Y.
Published: July 2002

A simple model for charged dusts in plasmas is considered. The interaction of the dusts with the electron–ion plasma background yields a dust–dust interaction force that is attractive. The latter can hold the dust grains in various stable and metastable cluster configurations. The predicted few-dust configurations agree well with the results from an experiment and a molecular dynamics simulation.
Effect of space-charge limited emission on measurements of plasma potential using emissive probes
Authors: Ye M. Y. , Takamura S.
Published: July 2002

Effects of space-charge limitation have been considered for an analytical estimation of plasma potential with use of emissive probes, taking account of a correct expression of emission current under space-charge limited condition. The analytical results are obtained for the floating potential method of emissive probe and for the differential emissive probe method, both without and with an oscillating ac potential. In the case of the floating potential method, the operating condition is discussed for different plasma parameters at several probe temperatures. These results indicate that the floating potential of the emissive probe gives us the plasma potential to an accuracy of the order of the plasma electron temperature Te/e for a strong probe emission. In the case of the differential emissive probe method, the relations among space-charge effects, the ratio of thermoelectron emission current to plasma electron collection current, the plasma electron temperature, the probe temperature, and the amplitude of the oscillating ac potential are discussed in terms of determination of plasma potential. In addition, the analytical results also indicate that the midpoint of the two peaks in the derivative d〈Iem〉/dV curve is a good method for measuring the time-averaged plasma potential.
Faulted dipoles in GaAs
Authors: De Cooman B. C. , Carter C. B.
Published: July 2002

Faulted dipoles in GaAs have been directly imaged by high-resolution transmission electron microscopy. The dislocation dipoles were introduced into the GaAs by deforming a sample in compression along a 〈110〉 axis. Both the Z character of the dipole and the intrinsic nature of the stacking faults could be determined directly from the high-resolution images. Using convergent-beam electron diffraction, it has been shown that it is possible to determine the polarity of the sample and thereby to differentiate between the α and β partial dislocations.
Photoluminescence and microstructural properties of high-temperature annealed buried oxide silicon-on-insulator
Authors: Duncan W. M. , Chang P.-H. , Mao B.-Y. , Chen C.-E.
Published: July 2002

The defect properties of buried oxide silicon-on-insulator (SOI) formed by high dose O+ ion implantation and annealed in the temperature range of 1150–1300 °C were examined using photoluminescence (PL) spectroscopy and transmission electron microscopy. The intensity of radiative defect levels at 0.814 and 0.862 eV measured by PL at 4.2 K was observed to decrease with increasing post-implantation annealing temperature. A direct correlation between the radiative defect band intensities and etch defect density in the top silicon layer was observed. The correlation between defect density and PL defect band intensity was further verified by cross-sectional transmission electron microscopy of the top silicon. This letter demonstrates for the first time the correlation between PL defect properties and microstructure of buried oxide SOI. From comparisons with radiative defect centers in oxygen precipitated and plastically deformed silicon, the radiative defect states in SOI silicon are shown to result from residual dislocations in the top silicon layer of the SOI structure.
Generator problem for certain property T factors
Authors: Ge Liming , Shen Junhao
Published: July 2002

We show that the property T factors associated with groups

SL
n

(Z),
n
≥ 3 are generated by two selfadjoint elements, one of which has an arbitrarily small support. This answers a question of Dan Voiculescu.
Four plasmepsins are active in thePlasmodium falciparumfood vacuole, including a protease with an active-site histidine
Authors: Banerjee Ritu , Liu Jun , Beatty Wandy , Pelosof Lorraine , Klemba Michael , Goldberg Daniel E.
Published: July 2002

Hemoglobin degradation is a metabolic process that is central to the growth and maturation of the malaria parasitePlasmodium falciparum. Two aspartic proteases that initiate degradation, plasmepsins (PMs) I and II, have been identified and extensively characterized. Eight additional PM genes are present in theP. falciparumgenome. To better understand the enzymology of hemoglobin degradation, it is necessary to determine which of these genes are expressed when hemoglobin degradation is occurring, which encode active enzymes, and which gene products are found in the food vacuole where catabolism takes place. Our genome-wide analysis reveals that PM I, II, and IV and histo-aspartic protease encode hemoglobin-degrading food vacuole proteases. Despite having a histidine in place of one of the catalytic aspartic acids conserved in other aspartic proteases, histo-aspartic protease is an active hydrolase.
Vaccination for protection of retinal ganglion cells against death from glutamate cytotoxicity and ocular hypertension: Implications for glaucoma
Authors: Schori Hadas , Kipnis Jonathan , Yoles Eti , WoldeMussie Elizabeth , Ruiz Guadalupe , Wheeler Larry A. , Schwartz Michal
Published: July 2002

Our group recently demonstrated that autoimmune T cells directed against central nervous system-associated myelin antigens protect neurons from secondary degeneration. We further showed that the synthetic peptide copolymer 1 (Cop-1), known to suppress experimental autoimmune encephalomyelitis, can be safely substituted for the natural myelin antigen in both passive and active immunization for neuroprotection of the injured optic nerve. Here we attempted to determine whether similar immunizations are protective from retinal ganglion cell loss resulting from a direct biochemical insult caused, for example, by glutamate (a major mediator of degeneration in acute and chronic optic nerve insults) and in a rat model of ocular hypertension. Passive immunization with T cells reactive to myelin basic protein or active immunization with myelin oligodendrocyte glycoprotein-derived peptide, although neuroprotective after optic nerve injury, was ineffective against glutamate toxicity in mice and rats. In contrast, the number of surviving retinal ganglion cells per square millimeter in glutamate-injected retinas was significantly larger in mice immunized 10 days previously with Cop-1 emulsified in complete Freund's adjuvant than in mice injected with PBS in the same adjuvant (2,133 ± 270 and 1,329 ± 121, respectively, mean ± SEM;P< 0.02). A similar pattern was observed when mice were immunized on the day of glutamate injection (1,777 ± 101 compared with 1,414 ± 36;P< 0.05), but not when they were immunized 48 h later. These findings suggest that protection from glutamate toxicity requires reinforcement of the immune system by antigens that are different from those associated with myelin. The use of Cop-1 apparently circumvents this antigen specificity barrier. In the rat ocular hypertension model, which simulates glaucoma, immunization with Cop-1 significantly reduced the retinal ganglion cell loss from 27.8% ± 6.8% to 4.3% ± 1.6%, without affecting the intraocular pressure. This study may point the way to a therapy for glaucoma, a neurodegenerative disease of the optic nerve often associated with increased intraocular pressure, as well as for acute and chronic degenerative disorders in which glutamate is a prominent participant.
Mammalian inositol polyphosphate multikinase synthesizes inositol 1,4,5-trisphosphate and an inositol pyrophosphate
Authors: Saiardi Adolfo , Nagata Eiichiro , Luo Hongbo R. , Sawa Akira , Luo Xiaojiang , Snowman Adele M. , Snyder Solomon H.
Published: July 2002

Using a consensus sequence in inositol phosphate kinase, we have identified and cloned a 44-kDa mammalian inositol phosphate kinase with broader catalytic capacities than any other member of the family and which we designate mammalian inositol phosphate multikinase (mIPMK). By phosphorylating inositol 4,5-bisphosphate, mIPMK provides an alternative biosynthesis for inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. mIPMK also can form the pyrophosphate disphosphoinositol tetrakisphosphate (PP-InsP4) from InsP5. Additionally, mIPMK forms InsP4from Ins(1,4,5)P3and InsP5from Ins(1,3,4,5)P4.
Functional implications of the localization and activity of acid-sensitive channels in rat peripheral nervous system
Authors: Alvarez de la Rosa Diego , Zhang Ping , Shao Deren , White Fletcher , Canessa Cecilia M.
Published: July 2002

Acid-sensitive ion channels (ASIC) are proton-gated ion channels expressed in neurons of the mammalian central and peripheral nervous systems. The functional role of these channels is still uncertain, but they have been proposed to constitute mechanoreceptors and/or nociceptors. We have raised specific antibodies for ASIC1, ASIC2, ASIC3, and ASIC4 to examine the distribution of these proteins in neurons from dorsal root ganglia (DRG) and to determine their subcellular localization. Western blot analysis demonstrates that all four ASIC proteins are expressed in DRG and sciatic nerve. Immunohistochemical experiments and functional measurements of unitary currents from the ASICs with the patch–clamp technique indicate that ASIC1 localizes to the plasma membrane of small-, medium-, and large-diameter cells, whereas ASIC2 and ASIC3 are preferentially in medium to large cells. Neurons coexpressing ASIC2 and ASIC3 form predominantly heteromeric ASIC2–3 channels. Two spliced forms, ASIC2a and ASIC2b, colocalize in the same population of DRG neurons. Within cells, the ASICs are present mainly on the plasma membrane of the soma and cellular processes. Functional studies indicate that the pH sensitivity for inactivation of ASIC1 is much higher than the one for activation; hence, increases in proton concentration will inactivate the channel. These functional properties and localization in DRG have profound implications for the putative functional roles of ASICs in the nervous system.
The human programmed cell death-2 (PDCD2) gene is a target of BCL6 repression: Implications for a role of BCL6 in the down-regulation of apoptosis
Authors: Baron Beverly W. , Anastasi John , Thirman Michael J. , Furukawa Yoichi , Fears Scott , Kim David C. , Simone Federico , Birkenbach Mark , Montag Anthony , Sadhu Annamma , Zeleznik-Le Nancy , McKeithan Timothy W.
Published: July 2002

BCL6, a gene on chromosome 3 band q27, encodes aKruppel-type zinc finger transcriptional repressor. Rearrangements of this gene are frequent in various kinds of lymphomas, particularly of the large-cell B-cell type. The BCL6 nuclear phosphoprotein is expressed in a variety of tissues and is up-regulated particularly in lymph node germinal centers. The zinc fingers of BCL6 bind DNA in a sequence-specific manner. To identify targets of the BCL6 repressive effects, we used a VP16-BCL6 fusion protein containing the zinc fingers but devoid of the repressor domains to compete with the binding of endogenous BCL6 in a transiently transfected B-cell line and then performed subtractive hybridization by using a method to selectively amplify sequences that are differentially expressed. We found that the programmed cell death-2 (PDCD2) gene is a target of BCL6 repression. This gene is the human homolog ofRp8, a rat gene associated with programmed cell death in thymocytes. Immunohistochemistry reveals the anticipated inverse relationship between BCL6 and PDCD2 expression in human tonsil. PDCD2 is detectable in cells of the germinal center in areas where there is less BCL6 expression as well as in the mantle zone, where there is little or no BCL6 expression. These results raise the possibility that BCL6 may regulate apoptosis by means of its repressive effects on PDCD2. BCL6 deregulation may lead to persistent down-regulation of PDCD2, reduced apoptosis, and, as a consequence, accumulation of BCL6-containing lymphoma cells.
Defective trafficking and function of K
ATP
channels caused by a sulfonylurea receptor 1 mutation associated with persistent hyperinsulinemic hypoglycemia of infancy
Authors: Cartier Etienne A. , Conti Lisa R. , Vandenberg Carol A. , Shyng Show-Ling
Published: July 2002

The ATP-sensitive potassium channel (K
ATP
) regulates
insulin secretion in pancreatic β cells. Loss of functional
K
ATP
channels because of mutations in either the SUR1 or
Kir6.2 channel subunit causes persistent hyperinsulinemic hypoglycemia
of infancy (PHHI). We investigated the molecular mechanism by which a
single phenylalanine deletion in SUR1 (ΔF1388) causes PHHI. Previous
studies have shown that coexpression of ΔF1388 SUR1 with Kir6.2
results in no channel activity. We demonstrate here that the lack of
functional expression is due to failure of the mutant channel to
traffic to the cell surface. Trafficking of K
ATP
channels
requires that the endoplasmic reticulum-retention signal, RKR, present
in both SUR1 and Kir6.2, be shielded during channel assembly. To ask
whether ΔF1388 SUR1 forms functional channels with Kir6.2, we
inactivated the RKR signal in ΔF1388 SUR1 by mutation to AAA
(ΔF1388 SUR1
AAA
). Inactivation of similar endoplasmic
reticulum-retention signals in the cystic fibrosis transmembrane
conductance regulator has been shown to partially overcome the
trafficking defect of a cystic fibrosis transmembrane conductance
regulator mutation, ΔF508. We found that coexpression of ΔF1388
SUR1
AAA
with Kir6.2 led to partial surface expression of
the mutant channel. Moreover, mutant channels were active. Compared
with wild-type channels, the mutant channels have reduced ATP
sensitivity and do not respond to stimulation by MgADP or diazoxide.
The RKR → AAA mutation alone has no effect on channel properties. Our
results establish defective trafficking of K
ATP
channels as
a molecular basis of PHHI and show that F1388 in SUR1 is critical for
normal trafficking and function of K
ATP
channels.
KAT1 is not essential for stomatal opening
Authors: Szyroki Alexander , Ivashikina Natalya , Dietrich Petra , Roelfsema M. Rob G. , Ache Peter , Reintanz Birgit , Deeken Rosalia , Godde Matthias , Felle Hubert , Steinmeyer Ralf , Palme Klaus , Hedrich Rainer
Published: July 2002

It is generally accepted that K
+
uptake into guard
cells via inward-rectifying K
+
channels is required for
stomatal opening. To test whether the guard cell K
+
channel
KAT1 is essential for stomatal opening, a knockout mutant,
KAT1∷En-1
, was isolated from an
En-1
mutagenized
Arabidopsis thaliana
population. Stomatal
action and K
+
uptake, however, were not impaired in
KAT1-deficient plants. Reverse transcription–PCR experiments with
isolated guard cell protoplasts showed that in addition to KAT1, the
K
+
channels AKT1, AKT2/3, AtKC1, and KAT2 were expressed
in this cell type. In impalement measurements, intact guard cells
exhibited inward-rectifying K
+
currents across the plasma
membrane of both wild-type and
KAT1∷En-1
plants.
This study demonstrates that multiple K
+
channel
transcripts exist in guard cells and that KAT1 is not essential for
stomatal action.
AtKC1, a silent
Arabidopsis
potassium channel α-subunit modulates root hair K
+
influx
Authors: Reintanz Birgit , Szyroki Alexander , Ivashikina Natalya , Ache Peter , Godde Matthias , Becker Dirk , Palme Klaus , Hedrich Rainer
Published: July 2002

Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different α-subunits is largely unknown. Focusing on K
+
-selective ion channels, we have characterized AtKC1, a new α-subunit from the
Arabidopsis shaker
-like ion channel family. Promoter-β-glucuronidase (GUS) studies identified
AtKC1
expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K
+
channels α-subunits in root cells, we performed real-time reverse transcription–PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all
shaker
-like ion channel α-subunits, we only found the K
+
inward rectifier
AtKC1
and
AKT1
and the K
+
outward rectifier
GORK
to be expressed in this cell type.
Akt1
knockout plants essentially lacked inward rectifying K
+
currents. In contrast, inward rectifying K
+
currents were present in
AtKC1
knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 α-subunit represents an integral component of functional root hair K
+
uptake channels.
Structural studies of the scrapie prion protein by electron crystallography
Authors: Wille Holger , Michelitsch Melissa D. , Guénebaut Vincent , Supattapone Surachai , Serban Ana , Cohen Fred E. , Agard David A. , Prusiner Stanley B.
Published: July 2002

Because the insolubility of the scrapie prion protein (PrP
Sc
) has frustrated structural studies by x-ray crystallography or NMR spectroscopy, we used electron crystallography to characterize the structure of two infectious variants of the prion protein. Isomorphous two-dimensional crystals of the N-terminally truncated PrP
Sc
(PrP 27-30) and a miniprion (PrP
Sc
106) were identified by negative stain electron microscopy. Image processing allowed the extraction of limited structural information to 7 Å resolution. By comparing projection maps of PrP 27-30 and PrP
Sc
106, we visualized the 36-residue internal deletion of the miniprion and localized the N-linked sugars. The dimensions of the monomer and the locations of the deleted segment and sugars were used as constraints in the construction of models for PrP
Sc
. Only models featuring parallel β-helices as the key element could satisfy the constraints. These low-resolution projection maps and models have implications for understanding prion propagation and the pathogenesis of neurodegeneration.
Clustering of solitons in weakly correlated wavefronts
Authors: Chen Zhigang , Sears Suzanne M. , Martin Hector , Christodoulides Demetrios N. , Segev Mordechai
Published: July 2002

We demonstrate theoretically and experimentally the spontaneous clustering of solitons in partially coherent wavefronts during the final stages of pattern formation initiated by modulation instability and noise.
Dynamic properties of the Ras switch I region and its importance for binding to effectors
Authors: Spoerner Michael , Herrmann Christian , Vetter Ingrid R. , Kalbitzer Hans Robert , Wittinghofer Alfred
Published: July 2002

We have investigated the dynamic properties of the switch I region
of the GTP-binding protein Ras by using mutants of Thr-35, an invariant
residue necessary for the switch function. Here we show that these
mutants, previously used as partial loss-of-function mutations in
cell-based assays, have a reduced affinity to Ras effector proteins
without Thr-35 being involved in any interaction. The structure of
Ras(T35S)⋅GppNHp was determined by x-ray crystallography. Whereas
the overall structure is very similar to wildtype, residues from
switch I are completely invisible, indicating that the effector loop
region is highly mobile.
31
P-NMR data had indicated an
equilibrium between two rapidly interconverting conformations, one of
which (state 2) corresponds to the structure found in the complex with
the effectors.
31
P-NMR spectra of Ras mutants (T35S) and
(T35A) in the GppNHp form show that the equilibrium is shifted such
that they occur predominantly in the nonbinding conformation (state 1).
On addition of Ras effectors, Ras(T35S) but not Ras(T35A) shift to
positions corresponding to the binding conformation. The structural
data were correlated with kinetic experiments that show two-step
binding reaction of wild-type and (T35S)Ras with effectors requires the
existence of a rate-limiting isomerization step, which is not observed
with T35A. The results indicate that minor changes in the switch
region, such as removing the side chain methyl group of Thr-35,
drastically affect dynamic behavior and, in turn, interaction with
effectors. The dynamics of the switch I region appear to be responsible
for the conservation of this threonine residue in GTP-binding proteins.
Pituitary adenylate cyclase-activating polypeptide protects rat cerebellar granule neurons against ethanol-induced apoptotic cell death
Authors: Vaudry David , Rousselle Cécile , Basille Magali , Falluel-Morel Anthony , Pamantung Tommy F. , Fontaine Marc , Fournier Alain , Vaudry Hubert , Gonzalez Bruno J.
Published: July 2002

Alcohol exposure during development can cause brain malformations and neurobehavioral abnormalities. In view of the teratogenicity of ethanol, identification of molecules that could counteract the neurotoxic effects of alcohol deserves high priority. Here, we report that pituitary adenylate cyclase-activating polypeptide (PACAP) can prevent the deleterious effect of ethanol on neuronal precursors. Exposure of cultured cerebellar granule cells to ethanol inhibited neurite outgrowth and provoked apoptotic cell death. Incubation of granule cells with PACAP prevented ethanol-induced apoptosis, and this effect was not mimicked by vasoactive intestinal polypeptide, suggesting that PAC1 receptors are involved in the neurotrophic activity of PACAP. Ethanol exposure induced a strong increase of caspase-2, -3, -6, -8, and -9 activities, DNA fragmentation, and mitochondrial permeability. Cotreatment of granule cells with PACAP provoked a significant inhibition of all of the apoptotic markers investigated although the neurotrophic activity of PACAP could only be ascribed to inhibition of caspase-3 and -6 activities. These data demonstrate that PACAP is a potent protective agent against ethanol-induced neuronal cell death. The fact that PACAP prevented ethanol toxicity even when added 2 h after alcohol exposure, suggests that selective PACAP agonists could have potential therapeutic value for the treatment of fetal alcohol syndrome.
Mitochondrial and extramitochondrial apoptotic signaling pathways in cerebrocortical neurons
Authors: Budd Samantha L. , Tenneti Lalitha , Lishnak Timothy , Lipton Stuart A.
Published: July 2002

In cultured cerebrocortical neurons, mild excitotoxic insults or staurosporine result in apoptosis. We show here thatN-methyl-d-aspartate (NMDA) receptor-mediated, but not staurosporine-mediated, apoptosis is preceded by depolarization of the mitochondrial membrane potential (Δψm) and ATP loss. Both insults, however, release cytochromec(Cytc) into the cytoplasm. What prompts mitochondria to release Cytcand the mechanism of release are as yet unknown. We examined the effect of inhibition of the adenine nucleotide translocator (ANT), a putative component of the mitochondrial permeability transition pore. Inhibition of the mitochondrial ANT with bongkrekic acid (BA) prevented NMDA receptor-mediated apoptosis of cerebrocortical neurons. Concomitantly, BA prevented Δψmdepolarization, promoted recovery of cellular ATP content, and blocked caspase-3 activation. However, in the presence of BA, Cytcwas still released. Because BA prevented NMDA-induced caspase-3 activation and apoptosis, the presence of Cytcin the neuronal cytoplasm is not sufficient for the induction of caspase activity or apoptosis. In contrast to these findings, BA was ineffective in preventing staurosporine-induced activation of caspases or apoptosis. Additionally, staurosporine-induced, but not NMDA-induced, apoptosis was associated with activation of caspase-8. These results indicate that, in cerebrocortical cultures, excessive NMDA receptor activation precipitates neuronal apoptosis by means of mitochondrial dysfunction, whereas staurosporine utilizes a distinct pathway.
Structure and function correlation in histone H2A peptide-mediated gene transfer
Authors: Balicki Danuta , Putnam Christopher D. , Scaria Puthupparampil V. , Beutler Ernest
Published: July 2002

Histone H2A has been found to be efficient in DNA delivery into a number of cell lines. We have reasoned that this DNA-delivery activity is mediated by two mechanisms: (
i
) electrostatically driven DNA binding and condensation by histone and (
ii
) nuclear import of these histone H2A⋅DNA polyplexes via nuclear localization signals in the protein. We have identified a 37-aa N-terminal peptide of histone H2A that is active in
in vitro
gene transfer. This peptide can function as a nuclear localization signal and can bind DNA. Amino acid substitutions that replace positively charged residues and/or DNA-binding residues of this peptide obliterate transfection activity. The introduction of a proline in the first turn of an α-helix of this 37-mer obliterates transfection activity, suggesting that the integrity of the α-helical structure of the N-terminal region of histone H2A is related to its transfection activity.
Rescue of arrested replication forks by homologous recombination
Authors: Michel Bénédicte , Flores Maria-Jose , Viguera Enrique , Grompone Gianfranco , Seigneur Marie , Bidnenko Vladimir
Published: July 2002

DNA synthesis is an accurate and very processive phenomenon; nevertheless, replication fork progression on chromosomes can be impeded by DNA lesions, DNA secondary structures, or DNA-bound proteins. Elements interfering with the progression of replication forks have been reported to induce rearrangements and/or render homologous recombination essential for viability, in all organisms from bacteria to human. Arrested replication forks may be the target of nucleases, thereby providing a substrate for double-strand break repair enzyme. For example in bacteria, direct fork breakage was proposed to occur at replication forks blocked by a
bona fide
replication terminator sequence, a specific site that arrests bacterial chromosome replication. Alternatively, an arrested replication fork may be transformed into a recombination substrate by reversal of the forked structures. In reversed forks, the last duplicated portions of the template strands reanneal, allowing the newly synthesized strands to pair. In bacteria, this reaction was proposed to occur in replication mutants, in which fork arrest is caused by a defect in a replication protein, and in UV irradiated cells. Recent studies suggest that it may also occur in eukaryote organisms. We will review here observations that link replication hindrance with DNA rearrangements and the possible underlying molecular processes.
Traces, ideals, and arithmetic means
Authors: Kaftal Victor , Weiss Gary
Published: July 2002

This article grew out of recent work of Dykema, Figiel, Weiss, and Wodzicki (Commutator structure of operator ideals) which
inter alia
characterizes commutator ideals in terms of arithmetic means. In this paper we study ideals that are arithmetically mean (am) stable, am-closed, am-open, soft-edged and soft-complemented. We show that many of the ideals in the literature possess such properties. We apply these notions to prove that for all the ideals considered, the linear codimension of their commutator space (the “number of traces on the ideal”) is either 0, 1, or ∞. We identify the largest ideal which supports a unique nonsingular trace as the intersection of certain Lorentz ideals. An application to elementary operators is given. We study properties of arithmetic mean operations on ideals, e.g., we prove that the am-closure of a sum of ideals is the sum of their am-closures. We obtain cancellation properties for arithmetic means: for principal ideals, a necessary and sufficient condition for first order cancellations is the regularity of the generator; for second order cancellations, sufficient conditions are that the generator satisfies the exponential Δ
2
-condition or is regular. We construct an example where second order cancellation fails, thus settling an open question. We also consider cancellation properties for inclusions. And we find and use lattice properties of ideals associated with the existence of “gaps.”
Prostaglandins are required for CREB activation and cellular proliferation during liver regeneration
Authors: Rudnick David A. , Perlmutter David H. , Muglia Louis J.
Published: July 2002

The liver responds to multiple types of injury with an extraordinarily well orchestrated and tightly regulated form of regeneration. The response to partial hepatectomy has been used as a model system to elucidate the molecular basis of this regenerative response. In this study, we used cyclooxygenase (COX)-selective antagonists and -null mice to determine the role of prostaglandin signaling in the response of liver to partial hepatectomy. The results show that liver regeneration is markedly impaired when both COX-1 and COX-2 are inhibited by indocin or by a combination of the COX-1 selective antagonist, SC-560, and the COX-2 selective antagonist, SC-236. Inhibition of COX-2 alone partially inhibits regeneration whereas inhibition of COX-1 alone tends to delay regeneration. Neither the rise in IL-6 nor the activation of signal transducer and activator of transcription-3 (STAT3) that is seen during liver regeneration is inhibited by indocin or the selective COX antagonists. In contrast, indocin treatment prevents the activation of CREB by phosphorylation that occurs during hepatic regeneration. These data indicate that prostaglandin signaling is required during liver regeneration, that COX-2 plays a particularly important role but COX-1 is also involved, and implicate the activation of CREB rather than STAT3 as the mediator of prostaglandin signaling during liver regeneration.
Lightness constancy in primary visual cortex
Authors: MacEvoy Sean P. , Paradiso Michael A.
Published: July 2002

When the illumination of a visual scene changes, the quantity of light reflected from objects is altered. Despite this, the perceived lightness of the objects generally remains constant. This perceptual lightness constancy is thought to be important behaviorally for object recognition. Here we show that interactions from outside the classical receptive fields of neurons in primary visual cortex modulate neural responses in a way that makes them immune to changes in illumination, as is perception. This finding is consistent with the hypothesis that the responses of neurons in primary visual cortex carry information about surface lightness in addition to information about form. It also suggests that lightness constancy, which is sometimes thought to involve “higher-level” processes, is manifest at the first stage of visual cortical processing.
Ultrahigh-resolution multicolor colocalization of single fluorescent probes
Authors: Lacoste Thilo D. , Michalet Xavier , Pinaud Fabien , Chemla Daniel S. , Alivisatos A. Paul , Weiss Shimon
Published: July 2002

An optical ruler based on ultrahigh-resolution colocalization of single fluorescent probes is described in this paper. It relies on the use of two unique families of fluorophores, namely energy-transfer fluorescent beads (TransFluoSpheres) and semiconductor nanocrystal quantum dots, that can be excited by a single laser wavelength but emit at different wavelengths. A multicolor sample-scanning confocal microscope was constructed that allows one to image each fluorescent light emitter, free of chromatic aberrations, by scanning the sample with nanometer scale steps with a piezo-scanner. The resulting spots are accurately localized by fitting them to the known shape of the excitation point-spread function of the microscope. We present results of two-dimensional colocalization of TransFluoSpheres (40 nm in diameter) and of nanocrystals (3–10 nm in diameter) and demonstrate distance-measurement accuracy of better than 10 nm using conventional far-field optics. This ruler bridges the gap between fluorescence resonance energy transfer, near- and far-field imaging, spanning a range of a few nanometers to tens of micrometers.