Biosynthetic pathway of mitochondrial ATPase subunit 9 in Neurospora crassa

Subunit 9 of mitochondrial ATPase (Su9) is synthesized in reticulocyte lysates programmed with Neurospora poly A-RNA, and in a Neurospora cell free system as a precursor with a higher apparent molecular weight than the mature protein (Mr 16,400 vs. 10,500). The RNA which directs the synthesis of Su9 precursor is associated with free polysomes. The precursor occurs as a high molecular weight aggregate in the postribosomal supernatant of reticulocyte lysates. Transfer in vitro of the precursor into isolated mitochondria is demonstrated. This process includes the correct proteolytic cleavage of the precursor to the mature form. After transfer, the protein acquires the following properties of the assembled subunit: it is resistant to added protease, it is soluble in chloroform/methanol, and it can be immunoprecipitated with antibodies to F1-ATPase. The precursor to Su9 is also detected in intact cells after pulse labeling. Processing in vivo takes place posttranslationally. It is inhibited by the uncoupler carbonylcyanide m- chlorophenylhydrazone (CCCP). A hypothetical mechanism is discussed for the intracellular transfer of Su9. It entails synthesis on free polysomes, release of the precursor into the cytosol, recognition by a receptor on the mitochondrial surface, and transfer into the inner mitochondrial membrane, which is accompanied by proteolytic cleavage and which depends on an electrical potential across the inner mitochondrial membrane

First-principles analysis of a homo-chiral cycloidal magnetic structure in a monolayer Cr on W(110)

The magnetic structure of a Cr monolayer on a W(110) substrate is investigated by means of first-principles calculations based on the noncollinear spin density functional theory (DFT). As magnetic ground state we find a long-period homochiral left-rotating spin spiral on-top of an atomic-scale anti-ferromagnetic order of nearest neighbor atoms. The rotation angle of the magnetic moment changes inhomogeneously from atom to atom across the spiral. We predict a propagation direction along the crystallographic [001] direction with a period length of 14.3 nm, which is in excellent agreement with a modulation of the local anti-ferromagnetic contrast observed in spin-polarized scanning tunneling microscope experiments by Santos et al. [New J. Phys. 10, 013005 (2008)]. We identify the Dzyaloshinskii-Moriya interaction (DMI) as origin of the homochiral magnetic structure, competing with the Heisenberg-type exchange interaction and magneto-crystalline anisotropy energy. From DFT calculations we extract parameters for a micromagnetic model and thereby determine a considerable inhomogeneity of the spin spiral, increasing the period length by 6% compared to homogeneous spin spirals. The results are compared to the behavior of a Mn and Fe monolayer and Fe doublelayer on a W(110) substrate

Role of Dzyaloshinskii-Moriya interaction for magnetism in transition-metal chains at Pt step-edges

We explore the emergence of chiral magnetism in one-dimensional monatomic Mn, Fe, and Co chains deposited at the Pt(664) step-edge carrying out an ab-initio study based on density functional theory (DFT). The results are analyzed employing several models: (i) a micromagnetic model, which takes into account the Dzyaloshinskii-Moriya interaction (DMI) besides the spin stiffness and the magnetic anisotropy energy, and (ii) the Fert-Levy model of the DMI for diluted magnetic impurities in metals. Due to the step-edge geometry, the direction of the Dzyaloshinskii vector (D-vector) is not predetermined by symmetry and points in an off-symmetry direction. For the Mn chain we predict a long-period cycloidal spin-spiral ground state of unique rotational sense on top of an otherwise atomic-scale antiferromagnetic phase. The spins rotate in a plane that is tilted relative to the Pt surface by $62^\circ$ towards the upper step of the surface. The Fe and Co chains show a ferromagnetic ground state since the DMI is too weak to overcome their respective magnetic anisotropy barriers. Beyond the discussion of the monatomic chains we provide general expressions relating ab-initio results to realistic model parameters that occur in a spin-lattice or in a micromagnetic model. We prove that a planar homogeneous spiral of classical spins with a given wave vector rotating in a plane whose normal is parallel to the D-vector is an exact stationary state solution of a spin-lattice model for a periodic solid that includes Heisenberg exchange and DMI. The validity of the Fert-Levy model for the evaluation of micromagnetic DMI parameters and for the analysis of ab-initio calculations is explored for chains. The results suggest that some care has to be taken when applying the model to infinite periodic one-dimensional systems.Comment: 21 pages, 9 figure

Bioverfügbarkeit, Bioakkumulation und Toxizität der Platingruppenelemente Pt, Pd und Rh in aquatischen Organismen

Bioverfügbarkeit, Bioakkumulation und Toxizität der Platingruppenelemente Pt, Pd und Rh in aquatischen Organismen Förderkennzeichen (BWBÖ 99008) Bernd Sures, Sonja Zimmermann: Zoologisches Institut I, Ökologie-Parasitologie, Geb. 30.43, Universität Karlsruhe, 76128 Karlsruhe Zusammenfassung Seit Beginn der 80iger Jahre werden in Deutschland durch den Einsatz von Autoabgas-katalysatoren in zunehmendem Umfang die katalytisch wirksamen Platingruppenelemente (PGE) Platin, Palladium und Rhodium emittiert. Jedoch ist bisher unklar, ob diese Metalle für die aquatische Biosphäre verfügbar sind, folglich aufgenommen und akkumuliert werden können. Ziel des hier vorgestellten Forschungsvorhabens ist es, mit verschiedenen aquatischen Organismen zunächst die Frage der Bioverfügbarkeit der Kfz-bürtigen PGE zu klären. Im Rahmen dieses Projektes konnte nun erstmalig nachgewiesen werden, dass das bisher aufgrund der schwierigen Spurenanalytik kaum untersuchte Pd bioverfügbar ist. Nach nur vierwöchiger Exposition von Aalen in Hälterungswasser mit Straßensediment (10 kg/100 l) fand sich in der Leber exponierter Aale eine mittlere Pd-Konzentration von 0,18 ± 0,05 ng/g (FS). Sobald die z.Z. noch laufenden Expositionsversuche abgeschlossen sind, lässt sich auch für Pt und Rh die Frage der Bioverfügbarkeit quantifizieren und das Ausmaß der PGE Akkumulation einschätzen. Summary Following the introduction of automobile catalysts in the middle of the 80th there is an increasing emission of the platinum-group-elements (PGE) platinum, palladium and rhodium. Still, it remains unclear if these metals are bioavailable for aquatic organisms and to which extent they become accumulated by the biosphere. To answer these questions experimental studies were conducted with aquatic animals maintained in water containing road dust (10 kg/100 l). Results from a four weeks exposure study revealed for the first time an uptake of automobile catalyst emitted Pd by European eels which showed a mean liver Pd concentration of 0.18 ± 0.05 ng/g (wet weight). By the end of the present exposure studies also the bioavailability of Pt and Rh as well as the degree of the PGE accumulation will become clear

Influence of complex disorder on skew-scattering Hall effects in L10L1_0-ordered FePt alloy

We show by first-principles calculations that the skew-scattering anomalous Hall and spin-Hall angles of L$1_0$-ordered FePt drastically depend on different types of disorder. A different sign of the AHE is obtained when slightly deviating from the stoichiometric ratio towards the Fe-rich side as compared to the Pt-rich side. For stoichiometric samples, short-range ordering of defects has a profound effect on the Hall angles and can change them by a factor of $2$ as compared to the case of uncorrelated disorder. This might explain the vast range of anomalous Hall angles measured in experiments, which undergo different preparation procedures and thus might differ in their crystallographic quality

Biological control of Helicoverpa armigera in Germany : the potential use of Trichogramma spp. and other parasitic hymenoptera

Der Nachweis von H.a. mit Pheromonfallen bleibt weiterhin problematisch, ist aber für die Terminierung eines Nützlingseinsatzes von grundlegender Bedeutung. Die Pheromone wirken nur im unmittelbaren Umfeld des Befalls, wie auch Untersuchungen in 2006 bestätigen. Eine Distanz von 0,5-1,0km kann bereits eine nicht ausreichende Monitoringwirkung bedeuten. Prinzipiell könnten mit Pheromonfallen lediglich bekannte Befallsfelder aus dem Vorjahr überwacht werden. Da der Schädling in diesem Falle jedoch zufliegt und nicht standortgebunden überwintert, kann er unter Umständen an ganz anderer Stelle auftreten. Ein weitererBaustein der neuen Beobachtungsstrategie ist daher, einen zentralen Befallsort südlich von Freiburg, der fast jährlich angeflogen wird, mit einem engen Netz (< 500m Abstand) an Pheromonfallen zu überwachen. Zudem werden Felder und Gewächshäuser, die in den letzten Jahren mit H.a. befallen waren, soweit sie gemeldet wurden und bekannt sind, weiter mit Pheromonfallen beobachtet. Da eine Überwinterung noch nicht nachgewiesen wurde, sollte die Überwachung im späten Frühjahr im Mai beginnen, mit einem Zuflug wird, je nach Witterungslage, in der Regel ab August zu rechnen sein.Helicoverpa armigera (H.a.) is a pest of growing importance in Germany. First observations of migrating individuals were made one month earlier since 2000 compared to 1975-1995. Due to an increasing mean summer temperature H.a. is migrating to South Germany in the middle of August, attacking tomato and ornamental plants in greenhouses, tobacco, sweet pepper and corn in the field. The monitoring strategy for H.a. has to be improved since pheromone trapping can not control the flight of migrating females. A combination of pheromone and light trapping and the use of attractants will be tested to observe the migrating pest. Egg parasitoids of the genus Trichogramma spp. (Trichogrammatidae) were selected for suitable indigenous strains. Specific strains from T. brassicae, T. cacoeciae and T. evanescens showed highest acceptance. The larval parasitoid Campoletis sp. (Ichneumonidae) was observed as natural enemy with 12% natural parasitism of H.a. larvae in tobacco in South Gemany. Bracon brevicornis (Braconidae) collected from Ostrinia nubilalis in 2006 is available in mass rearing and was successfully tested against H.a. in laboratory. A combined release of Trichogramma with B. brevicornis will be tested in 2007

RKKY-like contributions to the magnetic anisotropy energy: 3d adatoms on Pt(111) surface

The magnetic anisotropy energy defines the energy barrier that stabilizes a magnetic moment. Utilizing density functional theory based simulations and analytical formulations, we establish that this barrier is strongly modified by long-range contributions very similar to Frieden oscillations and Rudermann-Kittel-Kasuya-Yosida interactions. Thus, oscillations are expected and observed, with different decaying factors and highly anisotropic in realistic materials, which can switch non-trivially the sign of the magnetic anisotropy energy. This behavior is general and for illustration we address transition metals adatoms, Cr, Mn, Fe and Co deposited on Pt(111) surface. We explain in particular the mechanisms leading to the strong site-dependence of the magnetic anisotropy energy observed for Fe adatoms on Pt(111) surface as revealed previously via first-principles based simulations and inelastic scanning tunneling spectroscopy (A. A. Khajetoorians et al. Phys. Rev. Lett. 111, 157204 (2013)). The same mechanisms are probably active for the site-dependence of the magnetic anisotropy energy obtained for Fe adatoms on Pd or Rh(111) surfaces and for Co adatoms on Rh(111) surface (P. Blonski et al. Phys. Rev. B 81, 104426 (2010)).Comment: published manuscript with additional figures and comment

Spin-flip hot spots in ultrathin films of monovalent metals: Enhancement and anisotropy of the Elliott-Yafet parameter

In contrast to the long-known fact that spin-flip hot spots, i.e., special \vc{k}-points on the Fermi surface showing a high spin-mixing parameter, do not occur in the bulk of monovalent (noble and alkali) metals, we found them on the surface Brillouin-zone boundary of ultrathin films of these metals. Density-functional calculations within the Korringa-Kohn-Rostoker Green function method for ultrathin (001) oriented Cu, Ag, and Au films of 10-layer thickness show that the region around the hot spots can have a substantial contribution, e.g.\ 52\% in Au(001), to the integrated spin-mixing parameter, that could lead to a significant enhancement of the spin-relaxation rate or spin-Hall angle in thin films. Owing to the appearance of spin-flip hot-spots, a large anisotropy of the Elliott-Yafet parameter [50\% for Au(001)] is also found in these systems. The findings are important for spintronics applications in which noble-metals are frequently used and in which the dimensionality of the sample is reduced.Comment: 6 pages, 2 figure