bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice preamorphization by ion irradiation: Fluence dependence of the electronic stopping power threshold for amorphization
Authors: Agulló-López F. , García G. , Olivares J.
Published: April 2005

A thermal-spike model has been applied to characterize the damage structure of the latent tracks generated by high-energy ion irradiations on LiNbO3 through electron excitation mechanisms. It applies to ions having electronic stopping powers both below and above the threshold value for lattice amorphization. The model allows to estimate the defect concentrations in the heavily damaged (preamorphized) regions that have not reached the threshold for amorphization. They include the halo and tail surrounding the core of a latent track. The existence of the preamorphized regions accounts for a synergy between successive irradiations and predicts a dependence of the amorphization threshold on previous irradiation fluence. The predicted dependence is in accordance with irradiation experiments using N (4.53MeV), O (5.00MeV), F (5.13MeV), and Si (5 and 7.5MeV). For electronic stopping powers above the threshold value the model describes the generation of homogeneous amorphous layers and predicts the propagation of the amorphization front with fluence. A theoretical expression, describing this propagation, has been obtained that is in reasonable agreement with silicon irradiation experiments at 5 and 7.5MeV. The accordance is improved by including in a simple phenomenological way the velocity effect on the threshold. At the highest fluences (or depths) a significant discrepancy appears that may be attributed to the contribution of the nuclear collision damage.
Second-order superintegrable systems in conformally flat spaces. I. Two-dimensional classical structure theory
Authors: Kalnins E. G. , Kress J. M. , Miller W.
Published: April 2005

This paper is the first in a series that lays the groundwork for a structure and classification theory of second-order superintegrable systems, both classical and quantum, in conformally flat spaces. Many examples of such systems are known, and lists of possible systems have been determined for constant curvature spaces in two and three dimensions, as well as few other spaces. Observed features of these systems are multiseparability, closure of the quadratic algebra of second-order symmetries at order 6, use of representation theory of the quadratic algebra to derive spectral properties of the quantum Schrödinger operator, and a close relationship with exactly solvable and quasi-exactly solvable systems. Our approach is, rather than focus on particular spaces and systems, to use a general theoretical method based on integrability conditions to derive structure common to all systems. In this first paper we consider classical superintegrable systems on a general two-dimensional Riemannian manifold and uncover their common structure. We show that for superintegrable systems with nondegenerate potentials there exists a standard structure based on the algebra of 2×2 symmetric matrices, that such systems are necessarily multiseparable and that the quadratic algebra closes at level 6. Superintegrable systems with degenerate potentials are also analyzed. This is all done without making use of lists of systems, so that generalization to higher dimensions, where relatively few examples are known, is much easier.
Dynamic optical manipulation using intensity patterns directly projected by a reflective spatial light modulator
Authors: Tao S. H. , Yuan X.-C. , Niu H. B. , Peng X.
Published: April 2005

We propose a simple method to manipulate microparticles dynamically with intensity-modulated patterns projected by a spatial light modulator (SLM), on which the patterns are controlled by a computer directly. The patterns are intensity–intensity modulated by the SLM without involving any computation or algorithm. With the dynamic patterns we can manipulate particles interactively and visibly by drawing or mouse-dragging pictures or even playing a video file on the computer screen. Experimental observations verified the feasibility of the proposed technique as a simple and direct solution for interactive optical manipulation.
Polarized He3 gas compression system using metastability-exchange optical pumping
Authors: Hussey D. S. , Rich D. R. , Belov A. S. , Tong X. , Yang H. , Bailey C. , Keith C. D. , Hartfield J. , Hall G. D. R. , Black T. C. , Snow W. M. , Gentile T. R. , Chen W. C. , Jones G. L. , Wildman E.
Published: April 2005

Dense samples (10–100barcm) of nuclear spin polarized He3 are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high He3 polarizations (≈80%) at low pressures (few mbar). We describe a polarized He3 gas compressor system which accepts 0.26barlh−1 of He3 gas polarized to 70% by a 4W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5barcm target with final polarization of 55%. The spin relaxation rates of the system’s components have been measured using nuclear magnetic resonance and a model of the He3 polarization loss based on the measured relaxation rates and the gas flow is in agreement with a He3 polarization measurement using neutron transmission.
A refocusing modified velocity map imaging electron/ion spectrometer adapted to synchrotron radiation studies
Authors: Garcia Gustavo A. , Nahon Laurent , Harding Chris J. , Mikajlo Elisabeth A. , Powis Ivan
Published: April 2005

We present a modified velocity map imaging (VMI) spectrometer to be used in angle-resolved molecular photoionization studies in the gas phase with synchrotron radiation (SR) in the VUV/soft x-ray range. The main modifications as compared to the original design of Eppink and Parker [A. T. J. B. Eppink and D. H. Parker, Rev. Sci. Instrum. 68, 3477 (1997)] are an open repeller which allows the VMI spectrometer to be coupled to an independent dispersive electrostatic analyzer for combined operation in coincidence mode experiments, and the introduction of a coupled double Einzel lens in the flight tube in order to collect the full 4π solid angle for higher kinetic energy particles. The length and position of the lenses have been optimized by a genetic algorithm to obtain the maximum kinetic energy possible without compromising the energy resolution. Ray-tracing simulations and SR experiments show that the lenses can increase the kinetic energy bandwidth by a factor of up to 2.5. Furthermore, a remarkable improvement in the radial focusing of the particles’ momenta can be achieved when the lens array is operated in optimum fashion. The accuracy in the determination of the angular parameters, already satisfactory in the original VMI design, is not compromised by the lens operation. Experimentally, we succeeded in collecting 4π electrons with 14eV kinetic energy and 6% relative energy resolution with a detector of 36mm effective diameter, despite the larger ionization volume given by the SR as compared to laser multiphoton experiments. We predict that, by changing to a detector diameter of 70mm and reducing the focal length by a third, particles with energies up to 200eV could be collected by applying 10kV to the repeller electrode.
Atomically flat (110) SrTiO3 and heteroepitaxy
Authors: Mukunoki Y. , Nakagawa N. , Susaki T. , Hwang H. Y.
Published: April 2005

We have prepared an atomically flat and insulating (110) SrTiO3 surface by annealing at high temperature under varying oxygen partial pressure. At low pressure, the polar surface is stabilized by oxygen vacancies, resulting in an atomically flat surface characterized by (110) unit-cell steps. The vacancies can be filled while maintaining this surface structure, providing an atomically ideal (110) substrate. We demonstrate two-dimensional homoepitaxial and heteroepitaxial growth, establishing the potential of this growth orientation for controlling interface states arising from polarity discontinuities in perovskite heterostructures.
Infrared phototransistor using capacitively coupled two-dimensional electron gas layers
Authors: An Zhenghua , Chen Jeng-Chung , Ueda T. , Komiyama S. , Hirakawa K.
Published: April 2005

A narrow-band infrared phototransistor (14.8μm) is designed and realized based on a GaAs∕AlGaAs double-layer structure. An isolated island formed from the first quantum well (QW) works as a gate, which is capacitively coupled to the remote two-dimensional electron gas (2DEG) layer working as the source/drain channel. Incident radiation excites the intersubband transition within the isolated QW island. Excited electrons tunnel out of the QW causing it to positively charge up. This affects the conductance of the remote 2DEG channel, yielding detectable photosignals. The present detection mechanism makes it possible to design semiconductor infrared detectors with higher sensitivities along with custom designed tunability. The mechanism also holds potentiality of single-photon detection in the infrared region.
Decomposition of KH2PO4 crystals during laser-induced breakdown
Authors: Negres R. A. , Kucheyev S. O. , DeMange P. , Bostedt C. , van Buuren T. , Nelson A. J. , Demos S. G.
Published: April 2005

The structure of KH2PO4 single crystals (so-called KDP) irradiated with ∼3ns, 355 nm laser pulses with fluences above the laser-induced breakdown threshold is studied by a combination of Raman scattering, photoluminescence, and soft x-ray absorption spectroscopies. We compare spectra from the as-grown material, surface and bulk laser-induced damage sites, as well as from KPO3 references. Results show that irradiation with fluences above the laser-induced breakdown threshold leads to decomposition of KDP at surface damage sites but not at bulk damage sites. New spectroscopic features are attributed to dehydration products. For the laser irradiation conditions used in this study, the decomposed near-surface layer absorbs photons at ∼3.4eV (364 nm). These results may explain the recently reported fact that surface laser damage sites in KDP crystals tend to grow with subsequent exposure to high-power laser pulses, while bulk damage sites do not.
Exchange-bias stabilization of the magnetic nanoparticles in a granular alloy grown by reactive sputtering
Authors: Riveiro J. M. , De Toro J. A. , Andrés J. P. , González J. A. , Muñoz T. , Goff J. P.
Published: April 2005

The superparamagnetic blocking temperature of a series of granular Co22Ag78 alloys grown by reactive sputtering under oxygen atmosphere exhibits a minimum when plotted as a function of the oxygen pressure. The magnetic stabilization observed above this minimum is found to arise from the exchange-bias between the Co core and a CoO shell, which appears to be spin disordered. The initial decrease in the blocking temperature at low oxygen pressures is mainly attributed to the inhibition of RKKY-like interactions by the formation of an insulating oxide layer, too thin to give rise to exchange bias, around the ferromagnetic cores.
Enhanced electrophosphorescence via highly efficient energy transfer from conjugated polymer
Authors: Kim Tae-Ho , Yoo Dong-Hee , Park Jong Hyeok , Park O Ok , Yu Jae-Woong , Kim Jai Kyeong
Published: April 2005

We have demonstrated that efficient green electrophosphorescence is obtained via cascade energy transfer from poly(N-vinylcarbazole) (PVK) and host fluorescent polymer to the phosphorescent iridium complex. Efficient energy transfers from PVK to fluorescent polymer and then from this host polymer to iridium complex, fac-tris[2-(2-pyridinyl-kN)[5-(2,5-dimethylphenyl)phenyl]-kC]-iridium(III) [Ir(PDPP)3], were observed in the PVK/fluorescent polymer∕Ir(PDPP)3 blend system, even though the chemical compatibility between this fluorescent polymer and Ir(PDPP)3 is very poor. The phase separation between the host polymer and Ir(PDPP)3 was restrained and highly efficient energy transfer also occurred by blending with PVK which has the good chemical compatibility with both host and guest materials. The resulting device (indium tin oxide/PEDOT/blend layer/BCP/Li:Al alloy) reaches a maximum external quantum efficiency of 8.9% and a luminous efficiency of 32cd∕A.
Ecological controls on water-cycle response to climate variability in deserts
Authors: Scanlon B. R. , Levitt D. G. , Reedy R. C. , Keese K. E. , Sully M. J.
Published: April 2005

The impact of climate variability on the water cycle in desert ecosystems is controlled by biospheric feedback at interannual to millennial timescales. This paper describes a unique field dataset from weighing lysimeters beneath nonvegetated and vegetated systems that unequivocally demonstrates the role of vegetation dynamics in controlling water cycle response to interannual climate variability related to El Niño southern oscillation in the Mojave Desert. Extreme El Niño winter precipitation (2.3-2.5 times normal) typical of the U.S. Southwest would be expected to increase groundwater recharge, which is critical for water resources in semiarid and arid regions. However, lysimeter data indicate that rapid increases in vegetation productivity in response to elevated winter precipitation reduced soil water storage to half of that in a nonvegetated lysimeter, thereby precluding deep drainage below the root zone that would otherwise result in groundwater recharge. Vegetation dynamics have been controlling the water cycle in interdrainage desert areas throughout the U.S. Southwest, maintaining dry soil conditions and upward soil water flow since the last glacial period (10,000-15,000 yr ago), as shown by soil water chloride accumulations. Although measurements are specific to the U.S. Southwest, correlations between satellite-based vegetation productivity and elevated precipitation related to El Niño southern oscillation indicate this model may be applicable to desert basins globally. Understanding the two-way coupling between vegetation dynamics and the water cycle is critical for predicting how climate variability influences hydrology and water resources in water-limited landscapes.
Dual targeting of the protein disulfide isomerase RB60 to the chloroplast and the endoplasmic reticulum
Authors: Levitan Alexander , Trebitsh Tova , Kiss Vladimir , Pereg Yaron , Dangoor Inbal , Danon Avihai
Published: April 2005

RB60 is an atypical protein disulfide isomerase (PDI) that functions as a member of a redox regulatory protein complex controlling translation in the chloroplast of
Chlamydomonas reinhardtii
, but also contains a C-terminal endoplasmic reticulum (ER) retention signal, -KDEL. Here, we show by fluorescence microscopy that RB60 resides in the chloroplast but also outside of the chloroplast colocalized with BiP, an ER marker protein. RB60 accumulates in microsomes that exhibit a typical ER magnesium-shift, and cotranslationally translocates into ER microsomes. The first 50-aa leader of RB60 is sufficient for both chloroplast and ER targeting. The leader is cleaved upon translocation into the ER, whereas it remains intact after import to the chloroplast. The leader sequence also contains an acidic domain that appears necessary for the protein's association with the thylakoid membranes. Based on these and additional results, we propose that the dual localization of RB60 occurs via the two conserved transport mechanisms, to the chloroplast and to the ER, that the chloroplast RB60 most likely carries an additional function in the ER, and that its mode of transport, including the differential cleavage of its N terminus, plays an important role in its suborganellar localization and organellar-specific function.
Neuronal migration in the murine rostral migratory stream requires serum response factor
Authors: Alberti Siegfried , Krause Sven M. , Kretz Oliver , Philippar Ulrike , Lemberger Thomas , Casanova Emilio , Wiebel Franziska F. , Schwarz Heinz , Frotscher Michael , Schütz Günther , Nordheim Alfred
Published: April 2005

The central nervous system is fundamentally dependent on guided cell migration, both during development and in adulthood. We report an absolute requirement of the transcription factor serum response factor (SRF) for neuronal migration in the mouse forebrain. Conditional, late-prenatal deletion of
Srf
causes neurons to accumulate ectopically at the subventricular zone (SVZ), a prime neurogenic region in the brain. SRF-deficient cells of the SVZ exhibit impaired tangential chain migration along the rostral migratory stream into the olfactory bulb. SVZ explants display retarded chain migration
in vitro
. Regarding target genes, SRF deficiency impairs expression of the β-actin and gelsolin genes, accompanied by reduced cytoskeletal actin fiber density. At the posttranslational level, cofilin, a key regulator of actin dynamics, displays dramatically elevated inhibitory phosphorylation at Ser-3. Our studies indicate that SRF-controlled gene expression directs both the structure and dynamics of the actin microfilament, thereby determining cell-autonomous neuronal migration.
The human Kv1.1 channel is palmitoylated, modulating voltage sensing: Identification of a palmitoylation consensus sequence
Authors: Gubitosi-Klug Rose A. , Mancuso David J. , Gross Richard W.
Published: April 2005

Voltage-dependent K
+
channels rely on precise dynamic protein interactions with surrounding plasma membrane lipids to facilitate complex processes such as voltage sensing and channel gating. Many transmembrane-spanning proteins use palmitoylation to facilitate dynamic membrane interactions. Herein, we demonstrate that the human Kv1.1 ion channel is palmitoylated in the cytosolic portion of the S
2
-S
3
linker domain at residue C243. Through heterologous expression of the human Kv1.1 protein in Sf9 cells, covalent radiolabeling with [
3
H]palmitate, chemical stability studies of the [
3
H]-palmitoylated protein, and site-directed mutagenesis, C243 was identified as the predominant site of palmitoylation. The functional sequelae of palmitoylation were examined by analysis of whole cell currents from WT and mutant channels, which identified a 20-mV leftward shift in the current-voltage relationship when palmitoylation at C243 (but not with other cysteine deletions) is prevented by site-directed mutagenesis, implicating a role for palmitoylated C243 in modulating voltage sensing through protein-membrane interactions. Database searches identified an amino acid palmitoylation consensus motif (ACP/RSKT) that is present in multiple other members of the Shaker subfamily of K
+
channels and in several other unrelated regulatory proteins (e.g., CD36, nitric oxide synthase type 2, and the mannose-6 phosphate receptor) that are known to be palmitoylated by thioester linkages at the predicted consensus site cysteine residue. Collectively, these results (
i
) identify palmitoylation as a mechanism for K
+
channel interactions with plasma membrane lipids contributing to electric field-induced conformational alterations, and
ii
) define an amino acid consensus sequence for protein palmitoylation.
Postsynaptic assembly induced by neurexin-neuroligin interaction and neurotransmitter
Authors: Nam Christine I. , Chen Lu
Published: April 2005

Presynaptic and postsynaptic differentiation occurs at axodendritic contacts between CNS neurons. Synaptic adhesion mediated by synaptic cell adhesion molecule (SynCAM) and β-neurexins/neuroligins triggers presynaptic differentiation. The signals that trigger postsynaptic differentiation are, however, unknown. Here we report that β-neurexin expressed in nonneuronal cells induced postsynaptic density (PSD)-95 clustering in contacting dendrites of hippocampal neurons. The effect is specific to β-neurexin and was not observed with other synaptic cell adhesion molecules such as
N-
cadherin or SynCAM. NMDA receptors, but not α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate receptors (AMPARs), were recruited to this β-neurexin-induced PSD-95 scaffold. Remarkably, AMPARs were inserted into this scaffold upon glutamate application or expression of a constitutively active form of calmodulin kinase II in neurons. Expression of a dominant-negative neuroligin-1 in cultured neurons markedly reduced the sizes and densities of PSD-95 puncta and AMPAR clusters. In addition, excitatory, but not inhibitory, synaptic functions were impaired in these neurons, confirming that PSD-95/neuroligin-1 interaction is involved in postsynaptic assembly at glutamatergic synapses. These results demonstrate that postsynaptic assembly of the glutamatergic synapse may be initiated by presynaptic β-neurexin and that glutamate release also is required for maturation of synapses.
Neural crest stem cell maintenance by combinatorial Wnt and BMP signaling
Authors: Kléber Maurice , Lee Hye-Youn , Wurdak Heiko , Buchstaller Johanna , Riccomagno Martin M. , Ittner Lars M. , Suter Ueli , Epstein Douglas J. , Sommer Lukas
Published: April 2005

Canonical Wnt signaling instructively promotes sensory neurogenesis in early neural crest stem cells (eNCSCs) (Lee, H.Y., M. Kléber, L. Hari, V. Brault, U. Suter, M.M. Taketo, R. Kemler, and L. Sommer. 2004. Science. 303:1020–1023). However, during normal development Wnt signaling induces a sensory fate only in a subpopulation of eNCSCs while other cells maintain their stem cell features, despite the presence of Wnt activity. Hence, factors counteracting Wnt signaling must exist. Here, we show that bone morphogenic protein (BMP) signaling antagonizes the sensory fate-inducing activity of Wnt/β-catenin. Intriguingly, Wnt and BMP act synergistically to suppress differentiation and to maintain NCSC marker expression and multipotency. Similar to NCSCs in vivo, NCSCs maintained in culture alter their responsiveness to instructive growth factors with time. Thus, stem cell development is regulated by combinatorial growth factor activities that interact with changing cell-intrinsic cues.
Disulfide locked variants of factor VIIa with a restricted β‐strand conformation have enhanced enzymatic activity
Authors: Maun Henry R. , Eigenbrot Charles , Raab Helga , Arnott David , Phu Lilian , Bullens Sherron , Lazarus Robert A.
Published: April 2005

Proteolytic processing of zymogen Factor VII to Factor VIIa (FVIIa) is necessary but not sufficient for maximal proteolytic activity, which requires an additional allosteric influence induced upon binding to its cofactor tissue factor (TF). A key conformational change affecting the zymogenicity of FVIIa involves a unique three‐residue shift in the position of β‐strand B2 in their zymogen and protease forms. By selectively introducing new disulfide bonds, we locked the conformation of these strands into an active TF•FVIIa‐like state. FVIIa mutants designated 136:160, 137:159, 138:160, and 139:157, reflecting the position of the new disulfide bond (chymotypsinogen numbering), were expressed and purified by TF affinity chromatography. Mass spectrometric analysis of tryptic peptides from the FVIIa mutants confirmed the new disulfide bond formation. Kinetic analysis of amidolytic activity revealed that all FVIIa variants alone had increased specific activity compared to wild type, the largest being for variants 136:160 and 138:160 with substrate S‐2765, having 670‐ and 330‐fold increases, respectively. Notably, FVIIa disulfide‐locked variants no longer required TF as a cofactor for maximal activity in amidolytic assays. In the presence of soluble TF, activity was enhanced 20‐ and 12‐fold for variants 136:160 and 138:160, respectively, compared to wild type. With relipidated TF, mutants 136:160 and 137:159 also had an approximate threefold increase in their Vmax/Km values for FX activation but no significant improvement in TF‐dependent clotting assays. Thus, while large rate enhancements were obtained for amidolytic substrates binding at the active site, macro‐molecular substrates that bind to FVIIa exosites entail more complex catalytic requirements.
The evolutionary origins and catalytic importance of conserved electrostatic networks within TIM‐barrel proteins
Authors: Livesay Dennis R. , La David
Published: April 2005

Conservation of function is the basic tenet of protein evolution. Conservation of key electrostatic properties is a frequently employed mechanism that leads to conserved function. In a previous report, we identified several conserved electrostatic properties in four protein families and one functionally diverse enzyme superfamily. In this report, we demonstrate the evolutionary and catalytic importance of electrostatic networks in three ubiquitous metabolic enzymes: triosephosphate isomerase, enolase, and transaldolase. Evolutionary importance is demonstrated using phylogenetic motifs (sequence fragments that parallel the overall familial phylogeny). Phylogenetic motifs frequently correspond to both catalytic residues and conserved interactions that fine‐tune catalytic residue pKa values. Further, in the case of triosephosphate isomerase, quantitative differences in the catalytic Glu169 pKa values parallel subfamily differentiation. Finally, phylogenetic motifs are shown to structurally cluster around the active sites of eight different TIM‐barrel families. Depending upon the mechanistic requisites of each reaction catalyzed, interruptions to the canonical fold may or may not be identified as phylogenetic motifs.
Structural consequences of the familial amyotrophic lateral sclerosis SOD1 mutant His46Arg
Authors: Antonyuk Svetlana , Elam Jennifer Stine , Hough Michael A. , Strange Richard W. , Doucette Peter A. , Rodriguez Jorge A. , Hayward Lawrence J. , Valentine Joan Selverstone , Hart P. John , Hasnain S. Samar
Published: April 2005

The His46Arg (H46R) mutant of human copper‐zinc superoxide dismutase (SOD1) is associated with an unusual, slowly progressing form of familial amyotrophic lateral sclerosis (FALS). Here we describe in detail the crystal structures of pathogenic H46R SOD1 in the Zn‐loaded (Zn‐H46R) and metal‐free (apo‐H46R) forms. The Zn‐H46R structure demonstrates a novel zinc coordination that involves only three of the usual four liganding residues, His 63, His 80, and Asp 83 together with a water molecule. In addition, the Asp 124 “secondary bridge” between the copper‐ and zinc‐binding sites is disrupted, and the “electrostatic loop” and “zinc loop” elements are largely disordered. The apo‐H46R structure exhibits partial disorder in the electrostatic and zinc loop elements in three of the four dimers in the asymmetric unit, while the fourth has ordered loops due to crystal packing interactions. In both structures, nonnative SOD1–SOD1 interactions lead to the formation of higher‐order filamentous arrays. The disordered loop elements may increase the likelihood of protein aggregation in vivo, either with other H46R molecules or with other critical cellular components. Importantly, the binding of zinc is not sufficient to prevent the formation of nonnative interactions between pathogenic H46R molecules. The increased tendency to aggregate, even in the presence of Zn, arising from the loss of the secondary bridge is consistent with the observation of an increased abundance of hyaline inclusions in spinal motor neurons and supporting cells in H46R SOD1 transgenic rats.
Conversion of 5‐aminolevulinate synthase into a more active enzyme by linking the two subunits: Spectroscopic and kinetic properties
Authors: Zhang Junshun , Cheltsov Anton V. , Ferreira Gloria C.
Published: April 2005

The two active sites of dimeric 5‐aminolevulinate synthase (ALAS), a pyridoxal 5′‐phosphate (PLP)‐dependent enzyme, are located on the subunit interface with contribution of essential amino acids from each subunit. Linking the two subunits into a single polypeptide chain dimer (2XALAS) yielded an enzyme with an approximate sevenfold greater turnover number than that of wild‐type ALAS. Spectroscopic and kinetic properties of 2XALAS were investigated to explore the differences in the coenzyme structure and kinetic mechanism relative to those of wild‐type ALAS that confer a more active enzyme. The absorption spectra of both ALAS and 2XALAS had maxima at 410 and 330 nm, with a greater A410/A330 ratio at pH ∼7.5 for 2XALAS. The 330 nm absorption band showed an intense fluorescence at 385 nm but not at 510 nm, indicating that the 330 nm absorption species is the substituted aldamine rather than the enolimine form of the Schiff base. The 385 nm emission intensity increased with increasing pH with a single pK of ∼8.5 for both enzymes, and thus the 410 and 330 nm absorption species were attributed to the ketoenamine and substituted aldamine, respectively. Transient kinetic analysis of the formation and decay of the quinonoid intermediate EQ2 indicated that, although their rates were similar in ALAS and 2XALAS, accumulation of this intermediate was greater in the 2XALAS‐catalyzed reaction. Collectively, these results suggest that ketoenamine is the active form of the coenzyme and forms a more prominent coenzyme structure in 2XALAS than in ALAS at pH ∼7.5.
Fusogenic Alzheimer's peptide fragment Aβ (29–42) in interaction with lipid bilayers: Secondary structure, dynamics, and specific interaction with phosphatidyl ethanolamine polar heads as revealed by solid‐state NMR
Authors: Ravault Stéphanie , Soubias Olivier , Saurel Olivier , Thomas Annick , Brasseur Robert , Milon Alain
Published: April 2005

The interaction of the native Alzheimer's peptide C‐terminal fragment Aβ (29–42), and two mutants (G33A and G37A) with neutral lipid bilayers made of POPC and POPE in a 9:1 molar ratio was investigated by solid‐state NMR. This fragment and the lipid composition were selected because they represent the minimum requirement for the fusogenic activity of the Alzheimer's peptide. The chemical shifts of alanine methyl isotropic carbon were determined by MAS NMR, and they clearly demonstrated that the major form of the peptide equilibrated in membrane is not in a helical conformation. 2H NMR, performed with acyl chain deuterated POPC, demonstrated that there is no perturbation of the acyl chain's dynamics and of the lipid phase transition temperature. 2H NMR, performed with alanine methyl‐deuterated peptide demonstrated that the peptide itself has a limited mobility below and above the lipid phase transition temperature (molecular order parameter equal to 0.94). MAS 31P NMR revealed a specific interaction with POPE polar head as seen by the enhancement of POPE phosphorus nuclei T2 relaxation. All these results are in favor of a β‐sheet oligomeric association of the peptide at the bilayer interface, preferentially recruiting phosphatidyl ethanolamine polar heads.
Seasonal variations in the physiological status and energy content of somatic and reproductive tissues of chub
Authors: Encina L. , Granado‐Lorencio C.
Published: April 2005

The seasonal fluctuations in condition, nutrition and somatic energy content, and gonad development cycle were investigated in chub Leuciscus pyrenaicus from the headwaters of the Guadalete River, a freshwater ecosystem characterized by strong seasonal fluctuations in discharge and water level, temperature and food supply. The relationship between somatic stage and gonad cycle was also investigated and discussed. Condition, nutrition and somatic energy cycles could be divided into two distinct periods: from April to January with summer decreases and autumn increments, which is common for juveniles and mature fish; and from January to March, when juveniles and mature fish displayed different temporal variations related to the reproductive cycle. Gonad development took place from the end of the winter into the summer, the testes developing before the ovaries. Spawning started in late spring (May) and continued into summer (June and July), with fish quiescent by autumn (September). The results suggest that, for L. pyrenaicus, both environmental factors (e.g. food supply, water temperature) and reproduction needs affect the condition, nutrition and somatic energy storage of fish, which have been used as indicators of the physiological status of the population.
Morphological variation in intergrade pupfish populations from the Pecos River, Texas, U.S.A.
Authors: Wilde G. R. , Echelle A. A.
Published: April 2005

In the early 1980s, sheepshead minnow Cyprinodon variegates was introduced into the Pecos River, Texas, U.S.A. where it hybridized with the endemic Pecos pupfish C. pecosensis. By 1985, pupfish populations throughout approximately 300 km of the river consisted exclusively of individuals of hybrid origin (intergrades). There was significant (P <0·05) geographic variation in most morphological characters; the general pattern of variation was of a bidirectional cline centred near Pecos, Texas. At that site, morphology of intergrade populations resembled mostly that of the introduced species. Upstream and downstream from Pecos, morphology shifted progressively toward that typical of the native form. Intergrade populations were morphologically intermediate to the parental forms, showed a rapid approach to random assortment of characters, and generally exhibited greater morphological variability than occurred in either parent species. These observations and the consistent lack of bimodality in frequency distributions of a morphological hybrid index support the contention that intergrade populations comprise panmictic admixtures of C. variegates and C. pecosensis.
Orthodox and unorthodox phylogenetic relationships among tunas revealed by the nucleotide sequence analysis of the mitochondrial DNA control region
Authors: Alvarado Bremer J. R. , Naseri I. , Ely B.
Published: April 2005

A phylogeny of all eight recognized taxa of the genus Thunnus was constructed from approximately 400 base pairs of sequence of the mitochondrial DNA (mtDNA) control region. The PCR‐amplified control region I segment studied contained a total of 186 variable sites and 159 phylogenetically informative sites. Diagnostic sequences for every taxon were identified. Neighbour‐joining phylogenies supported monophyletic origins of the temperate subgenus Thunnus and of the tropical subgenus Neothunnus. Similar results were obtained by maximum parsimony analyses except that there was no support for a monophyletic origin of the subgenus Thunnus. Bigeye tuna, which have been difficult to place in either subgenus using conventional morphological data, was identified as the sister species of Neothunnus. Within the subgenus Thunnus, the Atlantic bluefin and Southern bluefin tunas were shown to be sister taxa of the highly divergent monophyletic clade formed by the Pacific northern bluefin and the Albacore tunas. The conspecific Atlantic (T. thynnus thynnus) and Pacific (T. t. orientalis) northern bluefin tunas were more divergent (Tamura‐Nei distance 0·145 ± 0·019) from each other than the average distance separating most species‐pairs within the genus. Thus, a re‐examination of their status as subspecies of T. thunnus is warranted.
Sperm structure and motility of the freshwater teleost Cottus gobio
Authors: Lahnsteiner F. , Berger B. , Weismann T. , Patzner R. A.
Published: April 2005

When motility of spermatozoa of Cottos gobio was initiated with distilled water, the motility rate decreased to 0% within 1 min, and significant signs of osmotic alterations were observed at the end of the motility period. By contrast, in 50 mmol 1−1 NaCl solution, the motility rate persisted for 120–140 min. In both distilled water and in 50 mmol 1−1 NaCl solution, the main swimming type of spermatozoa was linear motion during the whole motility period. The initial swimming velocity (50.0 ± 2.1 μm s−1) measured 10 s after motility initiation was similar in both distilled water and in 50 mmol 1−1 NaCl solution. In distilled water, the velocity decreased to <20 μm s−1 (locally motile) during the first minute of the motility phase. In 50 mmol 1−1 NaCl solutions, it remained at a constant level during the first 60 min of the motility period, but then started to decrease to <20 μm s−1 after 120 min. When 5 mmol 1−1 potassium cyanide, antimycin or atractyloside was added to the 50 mmol 1−1 NaCl solution, the motility period was reduced to ≤2min. Ten millimoles per litre 2‐deoxy‐D‐glucose, malonate or a mixture of 5 mmol 1−1 atractyloside and 5 mmol 1−1 carnithine did not effect the duration of the motility period. This indicates that sperm energy metabolism depends mainly on respiration rate and fatty acid metabolism.
The different banding patterns produced by restriction endonuclease digestion in mitotic chromosomes of the American and European eel
Authors: Salvadori S. , Deiana A. M. , Coluccia E. , Milia A. , Cau A.
Published: April 2005

The detection of three classes of C‐heterochromatin by in situ restriction endonuclease digestion allowed a karyotype differentiation between the American and the European eel.
In vitro steroid production by isolated ovarian follicles of the striped trumpeter
Authors: Pankhurst N. W.
Published: April 2005

Ovarian follicles from striped trumpeter Latris lineata were incubated in L15 medium alone, or medium supplemented with gonadotropin (GtH) preparations (human chorionic GtH, carp maturational GtH or partially purified salmon GtH), testosterone (T) or 17‐hydroxyprogesterone (17P). Levels of oestrone (E1), 17β‐oestradiol (E2), T, and 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20βP) in the medium after incubation were measured by radioimmunoassay. Basal production of E2 was high from previtellogenic follicles, whereas little T was produced. Both T and E2 production increased in response to treatment with GtH or steroid precursors. Vitellogenic follicles showed basal production of both T and E2, and T but not E2 levels generally increased in response to hormone treatment. Preparations containing follicles nearing final maturation showed low basal production of E2 but high production of T. Treatment with steroids resulted in little change in E2 but often very large increases in T production, whereas GtH stimulated lesser increases. 17,20βP production was detectable from incubations of maturing follicles from two out of five fish, and in those two incubations, increased in response to treatment with 17P. E1 was not detectable in any incubations. The results indicate that there is a shift in steroidogenesis from E2 to T production during oocyte development, and provide further evidence that steroid biosynthesis in non‐salmonids is principally regulated by substrate availability.
Swimming performance of various freshwater Newfoundland salmonids relative to habitat selection and fishway design
Authors: Peake S. , McKinley R. S. , Scruton D. A.
Published: April 2005

Swimming ability of wild brook trout Salvelinus fontinalis, brown trout Salmo trutta, anadromous Atlantic salmon Salmo salar, and landlocked Atlantic salmon was examined using fixed and increasing velocity tests. Although brook trout and salmon parr were collected from the same site, brook trout were found generally in slow‐moving pools whereas salmon were more common in faster riffle areas. Salmon parr could hold station indefinitely in currents in which brook trout could only maintain themselves briefly. Therefore, selection of fast‐water areas by salmon parr may impose a velocity barrier to sympatric juvenile brook trout, reducing competition between the species. Performance comparisons also indicate that anadromous Atlantic salmon possess slightly greater sustained ability than landlocked salmon, possibly due to altered selective pressure associated with their different life histories. Finally, fishways and culverts in Newfoundland can now be designed using models generated from performance data collected from native salmonid species.
Reproductive cycles in a reared strain of the mummichog, a daily spawner
Authors: Shimizu A.
Published: April 2005

Annual, lunar, and diel samplings were taken from a strain of mummichog (Arasaki strain) reared in outdoor tanks under natural conditions, to examine gonadal maturity. Gonads of yearling fish were quite immature in September. During late autumn and winter, a gradual increase in the GSI of both sexes was observed, and the growth of cortical alveolus phase oocytes in females and basal spermatogenesis in males progressed. In late February, a rapid increase in the GSI of both sexes, vitellogenesis in females, and active spermatogenesis in males, occurred. The spawning period of the yearling fish was from late March to August judging from the presence of milt‐producing males and ovulated females. The spawning period of the underyearling fish started in the same month as the yearlings, but terminated 1 month earlier. Plasma levels of oestradiol‐17β (E2) in females and testosterone in males were high during the spawning period in the yearlings. In the underyearlings, however, E2 levels peaked in early spring, and declined in the latter part of the spawning period. Neither a lunar nor semilunar cycle was evident in the reproductive activity of this fish, which proved to be a typical daily spawner. Females showed an apparent daily reproductive cycle; oocyte maturation commenced at about 1200 hours, germinal vesicle breakdown (GVBD) occurred at about 2400 hours, and ovulation was completed by 2400 hours, 24 h after GVBD. Such clear annual and daily reproductive cycles make this strain of mummichog a suitable model for the study of environmental and endocrine regulation of reproductive cycles in marine and estuarine teleosts.
Histological and ultrastructural studies on the effects of hCG on sex inversion in the protogynous teleost Coris julis
Authors: Reinboth R. , Bnrusle‐Sicard S.
Published: April 2005

In the protogynous diandric teleost Coris julis, sex inversion can be induced by injection of human chorionic gonadotropin (hCG). The histological changes of the gonad are accompanied by a transformation of the female livery to that of secondary males. At the ultrastructural level, the presence of intragonadal primordial germ cells in spermatogonial nests and within the newly forming seminiferous lobules is shown. Leydig cells and granulocytes appear in the inverting gonads. The results support the assumption that gonadotropic hormone has a key role in protogynous sex change.
Growth, maturation and reproductive investment in Arctic charr
Authors: Adams C. E. , Huntingford F. A.
Published: April 2005

Size and rates of growth in a cohort of 1 + Arctic charr housed in standard conditions were tracked over 12 months (December to December) and mature and immature males and females compared retrospectively. In both sexes, maturing fish were larger than non‐maturing ones. In males, this size differential was the result of differences in growth in winter and early spring, but not in the remainder of the study period. In females, size differentials resulted mainly from growth rate differences immediately prior to breeding. In females but not in males, gonadosomatic index was predicted by growth rates in the months leading up to maturation, and among the females that matured, faster growing fish produced more eggs. Lipid reserves in July were correlated negatively with growth during the previous 7 months and, in females only, lipid reserves were significantly lower in maturing fish than in non‐maturing fish, indicating that mobilization of lipid energy reserves in maturing fish had commenced by this time. Variation in investment in gonadal tissue, measured as gonadosomatic index, was not explained by variation in July lipid reserves for either males or females. However, July lipid reserves were negatively correlated with egg number, so females investing more in ova exhibited greater depletion of lipid reserves. These results are discussed in the context of the relationship between body condition and the onset of maturation in salmonids, relative investment in reproduction and sexual differences in the cost of reproduction.
The impact of seasonal alteration in the lipid composition of broodstock diets on egg quality in the European sea bass
Authors: Navas J. M. , Bruce M. , Thrush M. , Farndale B. M. , Bromage N. , Zanuy S. , Carrillo M. , Bell J. G. , Ramos J.
Published: April 2005

Groups of European sea bass Dicentrarchus labrax L., broodstock were fed two pelleted, lipid‐enriched diets [maize oil, low essential fatty acid (EFA) or fish oil, high EFA]. Those fed the high EFA diet for 12 months or only during vitellogenesis (September to February) with the low EFA diet fed for the remaining 6 months, showed improved egg quality and higher hatching rates when compared to two groups fed the high EFA diet during either previtel‐logenesis (February to September) or the spawning period (February to April). The higher quality eggs contained higher levels of total n‐3 fatty acids, including increased levels of both docosahexaenoic acid (DHA) and eicosapaentaenoic acid (EPA). High levels of triacylglycerol (TAG) were linked with the poorer quality eggs from those groups fed the low EFA diet during the period of vitellogenesis. The present work identifies vitellogenesis as the period in the maturation during which EFA are incorporated most effectively into the developing oocytes.
Tilapia are able to withstand long‐term exposure to low environmental pH, judged by their energy status, ionic balance and plasma cortisol
Authors: Van Ginneken V. J. T. , Van Eersel R. , Balm P. , Nieveen M. , Van Den Thillart G.
Published: April 2005

Tilapia Oreochromis mossambicus were exposed to water at pH 4·0 for 37 days. The water was acidified slowly over 6 h enabling the animals to acclimate and preventing damage of the gill epithelium. Additional stressors, e.g. aluminium ions and handling stress, were avoided. No mortality or decreased food consumption was observed during the exposure period. No significant changes were observed between the control and acid exposed groups for the energy rich compounds and related parameters, i.e. the adenylate energy charge, the pool of total adenine nucleotides, and the IMP load of white muscle and liver, indicating maintenance of homeostasis. Moreover, there were no significant differences between control groups and acidified groups at 3, 17 and 37 days for plasma sodium, chloride, cortisol and glucose, implying that ionic balance was maintained and that there was no activation of the pituitary‐interrenal axis. It is concluded that tilapia can acclimate to water at pH 4·0 when the acidification rate is slow and additional stressors are avoided.
Field metabolic rates of rainbow trout estimated using electromyogram telemetry
Authors: Briggs C. T. , Post J. R.
Published: April 2005

Field metabolic rates (FMR) of five rainbow trout were estimated using electromyogram (EMG) telemetry of the axial muscle. A series of laboratory experiments indicated that the EMG transmitter output was related strongly to total oxygen consumption of the fish over a wide range of swimming speeds and temperatures. No differences were evident when the oxygen consumption v. EMG relationship for routine swimming was compared with that for forced swimming. FMR was assessed on two time scales, revealing diel patterns and seasonal patterns. On the diel scale, the FMR pattern could be classified as crepuscular. At the upper and lower limits of temperature tolerance, the diel pattern was less distinct. On the seasonal scale, mean daily FMR was strongly dependent on mean environmental temperature. Comparisons between FMR and laboratory derived estimates of standard and maximally active metabolism indicate that the rainbow trout in the field utilize <20% of the available scope for activity.
Infrasound produces flight and avoidance responses in Pacific juvenile salmonids
Authors: Knudsen F. R. , Schreck C. B. , Knapp S. M. , Enger P. S. , Sand O.
Published: April 2005

A 10‐Hz frequency sound caused flight or avoidance responses in juvenile spring chinook salmon Oncorhynchus tshawytscha and rainbow trout O. mykiss. Groups of fish were placed in 3‐m diameter circular tanks with a water depth of 1 m. The sound source was a 25‐cm diameter aluminium tube with a piston in one end. The piston was driven back and forth by an eccentric coupling to an electric motor at a frequency of 10 Hz and with peak to peak amplitude of 4 cm. The sound source was turned on for 5 s when the fish was within 1 m. Initial tests always resulted in a strong flight response, but after three to four tests the fish more typically simply swam away as far as possible from the source. This avoidance response did not habituate even after 20 trials.