Some aspects of the hydrolysis of phosphomonoesters by homogenates of growing and regressing mesonephroi in chick embryos

Résumé L'activité de la phosphatase acide envers le-glycérophosphate et le phénylphosphate a été comparée sous des conditions variées afin de constater si ces deux actions reflètent celle de molécules enzymatiques pareilles ou différentes pendant la croissance et la régression du mésonéphros chez l'embryon de poulet. Pour élucider cette question, on a étudié les effets de la température au pH 5, et du versène, et l'influence d'un substratum sur l'hydrolyse. Les résultats de ces recherches indiquent que la même enzyme pourrait être responsable de l'hydrolyse de ces 2 substrats.

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This investigation was supported by NIH Training Grant No. HD-00012.     

A giant gamma-ray flare from the magnetar SGR 1806-20

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.     

A disk of dust and molecular gas around a high-mass protostar

The processes leading to the birth of low-mass stars such as our Sun have been well studied, but the formation of high-mass (over eight times the Sun's mass, M(o)) stars remains poorly understood. Recent studies suggest that high-mass stars may form through accretion of material from a circumstellar disk, in essentially the same way as low-mass stars form, rather than through the merging of several low-mass stars. There is as yet, however, no conclusive evidence. Here we report the presence of a flattened disk-like structure around a massive 15M(o) protostar in the Cepheus A region, based on observations of continuum emission from the dust and line emission from the molecular gas. The disk has a radius of about 330 astronomical units (Au) and a mass of 1 to 8 M(o). It is oriented perpendicular to, and spatially coincident with, the central embedded powerful bipolar radio jet, just as is the case with low-mass stars, from which we conclude that high-mass stars can form through accretion.     

An origin for short gamma-ray bursts unassociated with current star formation

Two short (< 2 s) gamma-ray bursts (GRBs) have recently been localized and fading afterglow counterparts detected. The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual gamma-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations. The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2-3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts--the coalescence of binary systems of neutron stars or a neutron star-black hole pair--are the progenitors of short bursts.     

Biotin and fatty acid biogenesis inAspergillus flavus

Zusammenfassung Avidin vermindert die Biosynthese von Fettsäuren inAspergillus flavus, die nur von Biotin überwunden wird. Ähnliche Phänomene werden in anderen Pilzen gefunden.     

CO2 activation on bimetallic CuNi nanoparticles

A trio of thiolate-protected atomically precise gold nanoclusters, [Au23(S-c-C6H11)16]–, Au24(SCH2pHtBu)20 and [Au25(SCH2CH2pH)18]–, are utilized as catalysts for 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP). Despite nearly identical sizes (~1 nm), the three nanoclusters possess distinctly different atomic packing structures and surface ligand binding modes, which contribute to different catalytic performance. The [Au23(S-c-C6H11)16]– nanocluster shows the highest activity with a kinetic rate constant of 0.0370 s?1, which is higher than those of Au24(SCH2pHtBu)20 (0.0090 s?1) and [Au25(SCH2CH2pH)18]– (0.0242 s?1). Such a trio of gold nanoclusters indicate that the atomic packing mode and electronic structure play a crucial role in determining their catalytic performance.     

The Arabidopsis lyrata genome sequence and the basis of rapid genome size change

We report the 207-Mb genome sequence of the North American Arabidopsis lyrata strain MN47 based on 8.3× dideoxy sequence coverage. We predict 32,670 genes in this outcrossing species compared to the 27,025 genes in the selfing species Arabidopsis thaliana. The much smaller 125-Mb genome of A. thaliana, which diverged from A. lyrata 10 million years ago, likely constitutes the derived state for the family. We found evidence for DNA loss from large-scale rearrangements, but most of the difference in genome size can be attributed to hundreds of thousands of small deletions, mostly in noncoding DNA and transposons. Analysis of deletions and insertions still segregating in A. thaliana indicates that the process of DNA loss is ongoing, suggesting pervasive selection for a smaller genome. The high-quality reference genome sequence for A. lyrata will be an important resource for functional, evolutionary and ecological studies in the genus Arabidopsis.