Stabilisation of Na,K-ATPase structure by the cardiotonic steroid ouabain

Cardiotonic steroids such as ouabain bind with high affinity to the membrane-bound cation-transporting P-type Na,K-ATPase, leading to complete inhibition of the enzyme. Using synchrotron radiation circular dichroism we show that the enzyme-ouabain complex is less susceptible to thermal denaturation (unfolding) than the ouabain-free enzyme, and this protection is observed with Na,K-ATPase purified from pig kidney as well as from shark rectal glands. It is also shown that detergent-solubilised preparations of Na,K-ATPase are stabilised by ouabain, which could account for the successful crystallisation of Na,K-ATPase in the ouabain-bound form. The secondary structure is not significantly affected by the binding of ouabain. Ouabain appears however, to induce a reorganization of the tertiary structure towards a more compact protein structure which is less prone to unfolding; recent crystal structures of the two enzymes are consistent with this interpretation. These circular dichroism spectroscopic studies in solution therefore provide complementary information to that provided by crystallography

Phonon engineering with superlattices: generalized nanomechanical potentials

Earlier implementations to simulate coherent wave propagation in one-dimensional potentials using acoustic phonons with gigahertz-terahertz frequencies were based on coupled nanoacoustic resonators. Here, we generalize the concept of adiabatic tuning of periodic superlattices for the implementation of effective one-dimensional potentials giving access to cases that cannot be realized by previously reported phonon engineering approaches, in particular the acoustic simulation of electrons and holes in a quantum well or a double well potential. In addition, the resulting structures are much more compact and hence experimentally feasible. We demonstrate that potential landscapes can be tailored with great versatility in these multilayered devices, apply this general method to the cases of parabolic, Morse and double-well potentials and study the resulting stationary phonon modes. The phonon cavities and potentials presented in this work could be probed by all-optical techniques like pump-probe coherent phonon generation and Brillouin scattering

EcoServe: Fokusgruppe med forbrugere. Værdien af urter i græsmarker for natur, dyr og mennesker

Smagen er altid det vigtigste. Natur, klima, bestøvere osv. er interessante mérværdier. Egoisme vs. holisme: Det er et dilemma at vælge det rigtige – tænk, hvis man kunne få både-og. Det ideelle er et produkt, som både smager godt og er godt for natur, dyr, miljø osv. Det er nemmere at vælge ”det gode”, hvis produktet ikke er så dyrt. ”Det gode” vil lettere sprede sig via et hverdagsprodukt – det nytter mere. Kommunikationen skal være enkel og konkret. Vi vil gerne have historier – men de skal bygge på fakta

Consumption that matters

The purpose of this article is to contribute to the understanding of a rising mode of ethical consumption by exploring the brand concept (RED) and its intertwinement of commerce and charity. Based on an analysis of central online media texts, we focus on: 1) the campaign’s “cool” visual and verbal structures of appeal, and 2) the discursive struggle concerning the ethical potential of consumption motivated by the campaign. The analysis is followed by a discussion of the potential and problems of (RED) as a way of handling global responsibility for distant suffering others. We argue that from a perspective focusing on the representation of the distant sufferer, (RED) can be criticised for transforming suffering into aesthetic spectacles in order to legitimise hedonistic consumption. The potential of the campaign is that it acknowledges that effective ethical ways of relating to distant others will have to be integrated into the narratives of self and community circulating in a given context

Fractional photon-assisted tunneling of ultra-cold atoms in periodically shaken double-well lattices

Fractional photon-assisted tunneling is investigated both numerically and analytically in a double-well lattice. While integer photon-assisted tunneling is a single-particle effect, fractional photon-assisted tunneling is an interaction-induced many-body effect. Double-well lattices with few particles in each double well are ideal to study this effect far from the mean-field effects. It is predicted that the 1/4-resonance is observable in such systems. Fractional photon-assisted tunneling provides a physically relevant model, for which N-th order time-dependent perturbation theory can be large although all previous orders are small. All predicted effects will be observable with an existing experimental setup [1]

Long-range effects of Na+ binding in Na,K-ATPase reported by ATP

This paper addresses the question of long-range interactions between the intramembranous cation binding sites and the cytoplasmic nucleotide binding site of the ubiquitous ion-transporting Na,K-ATPase using 13C cross-polarization magic-angle spinning (CP-MAS) solid-state NMR. High affinity ATP binding is induced by the presence of Na+ as well as of Na-like substances such as Tris+, and these ions are equally efficient promoters of nucleotide binding. CP-MAS analysis of bound ATP with Na,K-ATPase purified from pig kidney membranes reveals subtle differences in the nucleotide interactions within the nucleotide site depending on whether Na+ or Tris+ are used to induce binding. Differences in chemical shifts for ATP carbon atoms C1´ and C5´ observed in the presence of Na+ or Tris+ suggest alterations in the residues surrounding the bound nucleotide, hydrogen bonding and/or conformation of the ribose ring. This is taken as evidence for a long-distance communication between the Na+-filled ion sites in the membrane interior and the nucleotide binding site in the cytoplasmic domain and reflects the first conformational change ultimately leading to phosphorylation of the enzyme. Stopped-flow fluorescence measurements with the nucleotide analog eosin show that the dissociation rate constant for eosin is larger in Tris+ than in Na+, giving kinetic evidence for the difference in structural effects of Na+ and Tris+. According to the recent crystal structure of the E1•AlF4 -•ADP•3Na+-form the coupling between the ion binding sites and the nucleotide side is mediated by - among others - the M5-helix

Fractional photon-assisted tunneling in an optical superlattice: large contribution to particle transfer

Fractional photon-assisted tunneling is investigated both analytically and numerically for few interacting ultra-cold atoms in the double-wells of an optical superlattice. This can be realized experimentally by adding periodic shaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404 (2008)]. Photon-assisted tunneling is visible in the particle transfer between the wells of the individual double wells. In order to understand the physics of the photon-assisted tunneling, an effective model based on the rotating wave approximation is introduced. The validity of this effective approach is tested for wide parameter ranges which are accessible to experiments in double-well lattices. The effective model goes well beyond previous perturbation theory approaches and is useful to investigate in particular the fractional photon-assisted tunneling resonances. Analytic results on the level of the experimentally realizable two-particle quantum dynamics show very good agreement with the numerical solution of the time-dependent Schr\"odinger equation. Far from being a small effect, both the one-half-photon and the one-third-photon resonance are shown to have large effects on the particle transfer.Comment: 9 pages, 11 png-figure