44 research outputs found
Recovery of the X-Ray Transient QX Nor (=X1608-52) in Outburst and Quiescence
We present optical and near-IR observations of QX Nor, the counterpart to the
recurrent soft X-ray transient X1608-52, after its reappearance following the
X-ray outburst in February 1996. The object has been seen only once before,
during an X-ray outburst in 1977. Data from 3-5 months after the outburst show
the counterpart at a mean magnitude of R=20.2 and variable on timescales of
days. A comparison with identical observations in 1995 implies that the object
has brightened by at least 1.8 mag in R following the X-ray outburst. We also
detected QX Nor in the IR in both quiescence and outburst. A faint source is
visible in the J but not the R band in May 1995. These first observations in
the quiescent state yield magnitudes and colors consistent with optical
emission from a low mass companion in the binary system, as is true in other
soft X-ray transients.Comment: 10 pages including 4 figures and 2 tables; Uses AASTeX 4.0; Accepted
for publication in The Astrophysical Journal, Volume 485, August 20, 199
Relativistic precession around rotating neutron stars: Effects due to frame-dragging and stellar oblateness
General relativity predicts that a rotating body produces a frame-dragging
(or Lense-Thirring) effect: the orbital plane of a test particle in a
non-equatorial orbit precesses about the body's symmetry axis. In this paper we
compute the precession frequencies of circular orbits around rapidly rotating
neutron stars for a variety of masses and equations of state. The precession
frequencies computed are expressed as numerical functions of the orbital
frequency observed at infinity. The post-Newtonian expansion of the exact
precession formula is examined to identify the relative magnitudes of the
precession caused by the Lense-Thirring effect, the usual Newtonian quadrupole
effect and relativistic corrections. The first post-Newtonian correction to the
Newtonian quadrupole precession is derived in the limit of slow rotation. We
show that the post-Newtonian precession formula is a good approximation to the
exact precession close to the neutron star in the slow rotation limit (up to
\sim 400 Hz in the present context).
The results are applied to recent RXTE observations of neutron star low-mass
X-ray binaries, which display kHz quasi-periodic oscillations and, within the
framework of beat frequency models, allow the measurement of both the neutron
star spin frequency and the Keplerian frequency of the innermost ring of matter
in the accretion disk around it. For a wide range of realistic equations of
state, we find that the predicted precession frequency of this ring is close to
one half of the low-frequency (\sim 20 - 35 Hz) quasi-periodic oscillations
seen in several Atoll sources.Comment: 35 pages including 10 figures and 6 tables. To appear in the
Astrophysical Journa
New Results for Two Optically Faint Low Mass X-Ray Binary Systems
We present optical photometry of the low mass X-ray binary systems GX 349+2
and Ser X-1. Extensive VRI photometry of the faint optical counterpart (V=18.4)
to GX 349+2 reveals a period of 22.5 +/- 0.1 h and half-amplitude 0.2 mag. This
result confirms and extends our previously reported 22 h period. No color
change is detected over the orbit, although the limits are modest. We also
report the discovery of two new variable stars in the field of GX 349+2,
including a probable W UMa system. Ser X-1 is one of the most intense
persistent X-ray burst sources known. It is also one of only three burst
systems for which simultaneous optical and X-ray bursts have been observed. The
faint blue optical counterpart MM Ser (B~19.2) has long been known to have a
companion 2.1" distant. Our images indicate that MM Ser is itself a further
superposition of two stars, separated by only 1". At the very least, the ratio
of inferred burst to quiescent optical flux is affected by the discovery of
this additional component. In the worst case, the wrong object may have
previously been assumed as the optical counterpart.Comment: 16 pages including 10 figures and 3 tables; Uses AASTeX 4.0; Accepted
for publication in The Astrophysical Journal, Volume 490, November 20, 199
The Formation of Low-Mass Transient X-Ray Binaries
We consider constraints on the formation of low-mass X-ray binaries
containing neutron stars (NLMXBs) arising from the presence of soft X-ray
transients among these systems. We show that in short-period systems driven by
angular momentum loss these constraints require the secondary at the beginning
of mass transfer to have a mass > 1.2 M_sun, and to be significantly
nuclear-evolved. As a consequence a comparatively large fraction of such
systems appear as soft X-ray transients even at short periods, as observed.
Moreover the large initial secondary masses account for the rarity of NLMXBs at
periods less than 3 hr. In contrast, NLMXB populations forming with large kick
velocities would not have these properties, suggesting that the kick velocity
is generally small compared to the pre-SN orbital velocity in a large fraction
of systems. We derive constraints on progenitor system parameters and on the
strength of magnetic braking.Comment: Accepted for publication in ApJ, 19 pages, 4 figure
Perturbation of the yeast N-acetyltransferase NatB induces elevation of protein phosphorylation levels
<p>Abstract</p> <p>Background</p> <p>The addition of an acetyl group to protein N-termini is a widespread co-translational modification. NatB is one of the main N-acetyltransferases that targets a subset of proteins possessing an N-terminal methionine, but so far only a handful of substrates have been reported. Using a yeast <it>nat3Δ </it>strain, deficient for the catalytic subunit of NatB, we employed a quantitative proteomics strategy to identify NatB substrates and to characterize downstream effects in <it>nat3Δ</it>.</p> <p>Results</p> <p>Comparing by proteomics WT and <it>nat3Δ </it>strains, using metabolic <sup>15</sup>N isotope labeling, we confidently identified 59 NatB substrates, out of a total of 756 detected acetylated protein N-termini. We acquired in-depth proteome wide measurements of expression levels of about 2580 proteins. Most remarkably, NatB deletion led to a very significant change in protein phosphorylation.</p> <p>Conclusions</p> <p>Protein expression levels change only marginally in between WT and <it>nat3Δ</it>. A comparison of the detected NatB substrates with their orthologous revealed remarkably little conservation throughout the phylogenetic tree. We further present evidence of post-translational N-acetylation on protein variants at non-annotated N-termini. Moreover, analysis of downstream effects in <it>nat3Δ </it>revealed elevated protein phosphorylation levels whereby the kinase Snf1p is likely a key element in this process.</p
Hydrophilic interaction liquid chromatography (HILIC) in proteomics
In proteomics, nanoflow multidimensional chromatography is now the gold standard for the separation of complex mixtures of peptides as generated by in-solution digestion of whole-cell lysates. Ideally, the different stationary phases used in multidimensional chromatography should provide orthogonal separation characteristics. For this reason, the combination of strong cation exchange chromatography (SCX) and reversed-phase (RP) chromatography is the most widely used combination for the separation of peptides. Here, we review the potential of hydrophilic interaction liquid chromatography (HILIC) as a separation tool in the multidimensional separation of peptides in proteomics applications. Recent work has revealed that HILIC may provide an excellent alternative to SCX, possessing several advantages in the area of separation power and targeted analysis of protein post-translational modifications
Enhancing Europe’s global power: a scenario exercise with eight proposals
In the present context of intensifying competition between the major trading economies and potentially game-changing technological developments, the European Union is generally seen as the weaker party. Lacking the ‘hard power’ derived from military capabilities, it has laid claim to a ‘soft power’ of normative influence externally, yet even that is only partially utilised. Nor has Europe been able to exercise the power to coerce – ‘sharp power’ – commensurate with its economic weight as a trading bloc equivalent in size and reach to the US or China, its most prominent global competitors. How can Europe strengthen its position, and in what fields? Through a scenario exercise, we develop eight policy proposals aimed at countering Europe´s vulnerabilities and enabling it to assert its sharp and soft power more effectively. Specifically, we consider the feasibility, means and scope for their realisation. Together, they provide a transformative agenda for the EU’s position in the world
The Leukemia-Associated Mllt10/Af10-Dot1l Are Tcf4/β-Catenin Coactivators Essential for Intestinal Homeostasis
The leukemia-associated Mllt10/Af10 and its partner the histone methyltransferase Dot1l are identified as Tcf4/β-catenin co-activators and shown to be essential for Wnt-driven endogenous gene expression, intestinal development and homeostasis
Dimer interface of Bovine cytochrome c oxidase is influenced by local posttranslational modifications and lipid binding
Bovine cytochrome c oxidase is an integral membrane protein complex comprising 13 protein subunits and associated lipids. Dimerization of the complex has been proposed; however, definitive evidence for the dimer is lacking. We used advanced mass spectrometry methods to investigate the oligomeric state of cytochrome c oxidase and the potential role of lipids and posttranslational modifications in its subunit interfaces. Mass spectrometry of the intact protein complex revealed that both the monomer and the dimer are stabilized by large lipid entities. We identified these lipid species from the purified protein complex, thus implying that they interact specifically with the enzyme. We further identified phosphorylation and acetylation sites of cytochrome c oxidase, located in the peripheral subunits and in the dimer interface, respectively. Comparing our phosphorylation and acetylation sites with those found in previous studies of bovine, mouse, rat, and human cytochrome c oxidase, we found that whereas some acetylation sites within the dimer interface are conserved, suggesting a role for regulation and stabilization of the dimer, phosphorylation sites were less conserved and more transient. Our results therefore provide insights into the locations and interactions of lipids with acetylated residues within the dimer interface of this enzyme, and thereby contribute to a better understanding of its structure in the natural membrane. Moreover dimeric cytochrome c oxidase, comprising 20 transmembrane, six extramembrane subunits, and associated lipids, represents the largest integral membrane protein complex that has been transferred via electrospray intact into the gas phase of a mass spectrometer, representing a significant technological advance
NO/cGMP pathway in adrenomedullin mediated cardioprotection in mouse
Adrenomedullin (AM) limits experimental reperfusion injury due to Akt/eNOS signalling. We hypothesised that AM increases the NO pool and that cardioprotection is dependent on activation of soluble guanylyl cyclase (sGC).
Isolated hearts from CD31 mice were Langendorff-perfused. The left coronary artery was occluded for 30 min followed by 60 min reperfusion (R). AM 10 nM was administered from 15 min ischemia until 10 min reperfusion. Coronary effluent and LV myocardial samples were collected for nitrite (NO2−), nitrate (NO3−) and nitrosothiol (RNOS) analysis using reductive chemiluminescence. To examine the role of sGC, further hearts received the inhibitor ODQ 2 μM, alone or in combination with AM.
CAUC μM min2 mL− 1 LV myocardium μM
NO2− NO3− NO2− NO3−
10R 60R 10R 60R
Con 14.4 ± 2.8 6.1 ± .04 4.2 ± .8 4.6 ± .5 3.3 ± .3 3.8 ± .4
AM 29.2 ± 3.9* 7.2 ± .01* 3.9 ± .3 5.7 ± .4* 4.3 ± .7* 4.8 ± .5*
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CAUC = total clearance in coronary effluent at reperfusion. n = 4–5. *p < 0.05 1-way ANOVA vs. control.
AM increased RNOS 10 min after reperfusion (411 ± 60 nM vs. 221 ± 36 nM control, p < 0.05) and RV cGMP was elevated by 71% versus baseline. Infarct reduction by AM was blunted by sGC inhibition (AM 12.2 ± 2.3% vs. AM + ODQ 28.9 ± 4.3%, control 35.4 ± 2.7%, p < 0.05). We conclude that AM increases myocardial NO bioavailability and provides protection via the NO/sGC/cGMP pathway