Relativistic jet activity from the tidal disruption of a star by a massive black hole

Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.     

Quantum Metropolis sampling

The original motivation to build a quantum computer came from Feynman, who imagined a machine capable of simulating generic quantum mechanical systems--a task that is believed to be intractable for classical computers. Such a machine could have far-reaching applications in the simulation of many-body quantum physics in condensed-matter, chemical and high-energy systems. Part of Feynman's challenge was met by Lloyd, who showed how to approximately decompose the time evolution operator of interacting quantum particles into a short sequence of elementary gates, suitable for operation on a quantum computer. However, this left open the problem of how to simulate the equilibrium and static properties of quantum systems. This requires the preparation of ground and Gibbs states on a quantum computer. For classical systems, this problem is solved by the ubiquitous Metropolis algorithm, a method that has basically acquired a monopoly on the simulation of interacting particles. Here we demonstrate how to implement a quantum version of the Metropolis algorithm. This algorithm permits sampling directly from the eigenstates of the Hamiltonian, and thus evades the sign problem present in classical simulations. A small-scale implementation of this algorithm should be achievable with today's technology.     

The amine and amino acid composition in the Retzius cells of the leechHirudo medicinalis

Zusammenfassung Die Mikrochromatographie von dansylierten Verbindungen wurde angewandt, um die Verteilung von Aminen und Aminosäuren in den Retzius-Zellen und der Bauchganglienkette des BlutegelsHirudo medicinalis zu untersuchen. Die Retzius-Zellen weisen sehr grosse Mengen an Serotonin, 5-HTP und Tryptophan auf. Ihr Gehalt an Asparagin- und Glutaminsäure ist ebenfalls, allerdings in geringerem Masse, grösser als im umgebenoen Nervengewebe, während Histidin, Prolin, Valin, Alanin, Glycin sowie Threonin, Glutamin und Asparagin in geringeren Mengen vorkommen.

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We thank MissMarianne Maier for her technical assistance.

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Acknowledgment supported by a long term fellowship from the European Molecular Biological Organisation.     

A role for the two-helix finger of the SecA ATPase in protein translocation

An important step in the biosynthesis of many proteins is their partial or complete translocation across the plasma membrane in prokaryotes or the endoplasmic reticulum membrane in eukaryotes. In bacteria, secretory proteins are generally translocated after completion of their synthesis by the interaction of the cytoplasmic ATPase SecA and a protein-conducting channel formed by the SecY complex. How SecA moves substrates through the SecY channel is unclear. However, a recent structure of a SecA-SecY complex raises the possibility that the polypeptide chain is moved by a two-helix finger domain of SecA that is inserted into the cytoplasmic opening of the SecY channel. Here we have used disulphide-bridge crosslinking to show that the loop at the tip of the two-helix finger of Escherichia coli SecA interacts with a polypeptide chain right at the entrance into the SecY pore. Mutagenesis demonstrates that a tyrosine in the loop is particularly important for translocation, but can be replaced by some other bulky, hydrophobic residues. We propose that the two-helix finger of SecA moves a polypeptide chain into the SecY channel with the tyrosine providing the major contact with the substrate, a mechanism analogous to that suggested for hexameric, protein-translocating ATPases.     

Hormones in the translational control of early germination in wheat embryos

Gibberellic and abscisic acid seem to exert their effects on germination by acting in some way at the level of translation. The two hormones may act at different sites.     

Monoamine oxidase activity in Helix pomatia.

The distribution and characterization of MAO in various tissues of the snail were analyzed. Only low amounts of the enzyme exist in the different tissues and data suggest that there is more than one type of MAO.