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- Tanvir, N. R., et al.
(författare)
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A γ-ray burst at a redshift of z~8.2
- 2009
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 461, s. 1254-1257
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Tidskriftsartikel (refereegranskat)abstract
- Long-duration γ-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z>20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-α emitting galaxy. Here we report that GRB090423 lies at a redshift of z~8.2, implying that massive stars were being produced and dying as GRBs ~630Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.
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- Barthelmy, S D, et al.
(författare)
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An origin for short gamma-ray bursts unassociated with current star formation
- 2005
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 438, s. 994-996
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Tidskriftsartikel (refereegranskat)abstract
- Two short (< 2 s) gamma-ray bursts (GRBs) have recently been localized(1-4) and fading afterglow counterparts detected(2-4). 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(6-8). 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.
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- Göransson, Olga, et al.
(författare)
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Mechanism of action of A-769662, a valuable tool for activation of AMP-activated protein kinase
- 2007
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 282:45, s. 32549-32560
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the mechanism of A- 769662, a new activator of AMP- activated protein kinase ( AMPK). Unlike other pharmacological activators, it directly activates native rat AMPK by mimicking both effects of AMP, i. e. allosteric activation and inhibition of dephosphorylation. We found that it has no effect on the isolated alpha subunit kinase domain, with or without the associated autoinhibitory domain, or on interaction of glycogen with the beta subunit glycogen- binding domain. Although it mimics actions of AMP, it has no effect on binding of AMP to the isolated Bateman domains of the gamma subunit. The addition of A- 769662 to mouse embryonic fibroblasts or primary mouse hepatocytes stimulates phosphorylation of acetyl- CoA carboxylase ( ACC), effects that are completely abolished in AMPK- alpha 1(-/-) alpha 2(-/-) cells but not in TAK1(-/-) mouse embryonic fibroblasts. Phosphorylation of AMPK and ACC in response to A- 769662 is also abolished in isolated mouse skeletal muscle lacking LKB1, a major upstream kinase for AMPK in this tissue. However, in HeLa cells, which lack LKB1 but express the alternate upstream kinase calmodulin- dependent protein kinase kinase-beta, phosphorylation of AMPK and ACC in response to A- 769662 still occurs. These results show that in intact cells, the effects of A- 769662 are independent of the upstream kinase utilized. We propose that this direct and specific AMPK activator will be a valuable experimental tool to understand the physiological roles of AMPK.
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