226 research outputs found
Suzaku Observation of the Intermediate Polar V1223 Sagittarii
We report on the Suzaku observation of the intermediate polar V1223
Sagittarii. Using a multi-temperature plasma emission model with its reflection
from a cold matter, we obtained the shock temperature to be 37.9^{+5.1}_{-4.6}
keV. This constrains the mass and the radius of the white dwarf (WD) in the
ranges 0.82^{+0.05}_{-0.06} solar masses and (6.9+/-0.4)x10^8 cm, respectively,
with the aid of a WD mass-radius relation. The solid angle of the reflector
viewed from the post-shock plasma was measured to be Omega/2pi = 0.91+/-0.26. A
fluorescent iron Kalpha emission line is detected, whose central energy is
discovered to be modulated with the WD rotation for the first time in
magnetic-CVs. Detailed spectral analysis indicates that the line comprises of a
stable 6.4 keV component and a red-shifted component, the latter of which
appears only around the rotational intensity-minimum phase. The equivalent
width (EW) of the former stable component ~80 eV together with the measured
Omega indicates the major reflector is the WD surface, and the shock height is
not more than 7% of the WD radius. Comparing this limitation to the height
predicted by the Aizu model (1973), we estimated the fractional area onto which
the accretion occurs to be < 7x10^{-3}$ of the WD radius, which is the most
severe constraint in non-eclipsing IPs. The red-shifted iron line component, on
the other hand, can be interpreted as emanating from the pre-shock accretion
flow via fluorescence. Its EW (28^{+44}_{-13} eV) and the central energy
(6.30_{-0.05}^{+0.07} keV) at the intensity-minimum phase are consistent with
this interpretation.Comment: 25 pages, 13 figures, accepted for publication in PASJ (Suzaku & MAXI
special issue
GC/MS based metabolomics: development of a data mining system for metabolite identification by using soft independent modeling of class analogy (SIMCA)
<p>Abstract</p> <p>Background</p> <p>The goal of metabolomics analyses is a comprehensive and systematic understanding of all metabolites in biological samples. Many useful platforms have been developed to achieve this goal. Gas chromatography coupled to mass spectrometry (GC/MS) is a well-established analytical method in metabolomics study, and 200 to 500 peaks are routinely observed with one biological sample. However, only ~100 metabolites can be identified, and the remaining peaks are left as "unknowns".</p> <p>Result</p> <p>We present an algorithm that acquires more extensive metabolite information. Pearson's product-moment correlation coefficient and the Soft Independent Modeling of Class Analogy (SIMCA) method were combined to automatically identify and annotate unknown peaks, which tend to be missed in routine studies that employ manual processing.</p> <p>Conclusions</p> <p>Our data mining system can offer a wealth of metabolite information quickly and easily, and it provides new insights, particularly into food quality evaluation and prediction.</p
Ceramide Kinase Regulates Phospholipase C and Phosphatidylinositol 4, 5, Bisphosphate in Phototransduction
Phosphoinositide-specific phospholipase C (PLC) is a central effector for many biological responses regulated by G-protein-coupled receptors including Drosophila phototransduction where light sensitive channels are activated downstream of NORPA, a PLCbeta homolog. Here we show that the sphingolipid biosynthetic enzyme, ceramide kinase, is a novel regulator of PLC signaling and photoreceptor homeostasis. A mutation in ceramide kinase specifically leads to proteolysis of NORPA, consequent loss of PLC activity, and failure in light signal transduction. The mutant photoreceptors also undergo activity-dependent degeneration. Furthermore, we show that a significant increase in ceramide, resulting from lack of ceramide kinase, perturbs the membrane microenvironment of phosphatidylinositol 4, 5, bisphosphate (PIP(2)), altering its distribution. Fluorescence image correlation spectroscopic studies on model membranes suggest that an increase in ceramide decreases clustering of PIP(2) and its partitioning into ordered membrane domains. Thus ceramide kinase-mediated maintenance of ceramide level is important for the local regulation of PIP(2) and PLC during phototransduction
Suzaku Detection of Extended/Diffuse Hard X-Ray Emission from the Galactic Center
Five on-plane regions within +/- 0.8deg of the Galactic center were observed
with the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS)
onboard Suzaku. From all regions, significant hard X-ray emission was detected
with HXD-PIN up to 40 keV, in addition to the extended plasma emission which is
dominant in the XIS band. The hard X-ray signals are inferred to come primarily
from a spatially extended source, rather than from a small number of bright
discrete objects. Contributions to the HXD data from catalogued X-ray sources,
typically brighter than 1 mCrab, were estimated and removed using information
from Suzaku and other satellites. Even after this removal, the hard X-ray
signals remained significant, exhibiting a typical 12--40 keV surface
brightness of 4E-10 erg cm-2 s-1 deg-2 and power-law-like spectra with a photon
index of 1.8. Combined fittings to the XIS and HXD-PIN spectra confirm that a
separate hard tail component is superposed onto the hot thermal emission,
confirming a previous report based on the XIS data. Over the 5--40 keV band,
the hard tail is spectrally approximated by a power law of photon index ~2, but
better by those with somewhat convex shapes. Possible origins of the extended
hard X-ray emission are discussed.Comment: 13 pages, 18 figure
Defective cortex glia plasma membrane structure underlies light-induced epilepsy in cpes mutants
Seizures induced by visual stimulation (photosensitive epilepsy; PSE) represent a common type of epilepsy in humans, but the molecular mechanisms and genetic drivers underlying PSE remain unknown, and no good genetic animal models have been identified as yet. Here, we show an animal model of PSE, in Drosophila, owing to defective cortex glia. The cortex glial membranes are severely compromised in ceramide phosphoethanolamine synthase (cpes)-null mutants and fail to encapsulate the neuronal cell bodies in the Drosophila neuronal cortex. Expression of human sphingomyelin synthase 1, which synthesizes the closely related ceramide phosphocholine (sphingomyelin), rescues the cortex glial abnormalities and PSE, underscoring the evolutionarily conserved role of these lipids in glial membranes. Further, we show the compromise in plasma membrane structure that underlies the glial cell membrane collapse in cpes mutants and leads to the PSE phenotype
Discovery of Extended X-Ray emission from the unidentified TeV source HESS J1614-518 using the Suzaku Satellite
We report the Suzaku results of HESS J1614-518, which is the brightest
extended TeV gamma-ray source discovered in the Galactic plane survey conducted
using the H.E.S.S. telescope. We discovered three X-ray objects in the field of
view of the X-ray Imaging Spectrometer (XIS), which were designated as Suzaku
J1614-5141 (src A), Suzaku J1614-5152 (src B), and Suzaku J1614-5148 (src C).
Src A is an extended source located at the peak position of HESS J1614-518, and
therefore it is a plausible counterpart to HESS J1614-518. The X-ray flux in
the 2-10 keV band is 5e-13 erg/s/cm^2, which is an order of magnitude smaller
than the TeV flux. The photon index is 1.7, which is smaller than the canonical
value of synchrotron emissions from high-energy electrons found in some
supernova remnants. These findings present a challenge to models in which the
origin of the TeV emission is the inverse Compton scattering of the cosmic
microwave background by accelerated electrons that emit X-rays via synchrotron
emission. Src B is located at a relatively dim region in the TeV band image;
however, its hydrogen column density is the same as that of src A. Therefore,
src B may also be physically related to HESS J1614-518. Src C is a foreground
late-type B star. We also discovered a soft extended X-ray emission near HESS
J1614-518.Comment: Accepted for publication in PASJ vol. 60 Suzaku Special Issue
Enzyme systems involved in glucosinolate metabolism in Companilactobacillus farciminis KB1089
Cruciferous vegetables are rich sources of glucosinolates (GSLs). GSLs are degraded into isothiocyanates, which are potent anticarcinogens, by human gut bacteria. However, the mechanisms and enzymes involved in gut bacteria-mediated GSL metabolism are currently unclear. This study aimed to elucidate the enzymes involved in GSL metabolism in lactic acid bacteria, a type of gut bacteria. Companilactobacillus farciminis KB1089 was selected as a lactic acid bacteria strain model that metabolizes sinigrin, which is a GSL, into allylisothiocyanate. The sinigrin-metabolizing activity of this strain is induced under glucose-absent and sinigrin-present conditions. A quantitative comparative proteomic analysis was conducted and a total of 20 proteins that were specifically expressed in the induced cells were identified. Three candidate proteins, β-glucoside-specific IIB, IIC, IIA phosphotransferase system (PTS) components (CfPttS), 6-phospho-β-glucosidase (CfPbgS) and a hypothetical protein (CfNukS), were suspected to be involved in sinigrin-metabolism and were thus investigated further. We hypothesize a pathway for sinigrin degradation, wherein sinigrin is taken up and phosphorylated by CfPttS, and subsequently, the phosphorylated entity is degraded by CfPbgS. As expression of both pttS and pbgS genes clearly gave Escherichia coli host strain sinigrin converting activity, these genes were suggested to be responsible for sinigrin degradation. Furthermore, heterologous expression analysis using Lactococcus lactis suggested that CfPttS was important for sinigrin degradation and CfPbgS degraded phosphorylated sinigrin
Drosophila Sirt2/mammalian SIRT3 deacetylates ATP synthase beta and regulates complex V activity
Adenosine triphosphate (ATP) synthase beta, the catalytic subunit of mitochondrial complex V, synthesizes ATP. We show that ATP synthase beta is deacetylated by a human nicotinamide adenine dinucleotide (NAD(+))-dependent protein deacetylase, sirtuin 3, and its Drosophila melanogaster homologue, dSirt2. dsirt2 mutant flies displayed increased acetylation of specific Lys residues in ATP synthase beta and decreased complex V activity. Overexpression of dSirt2 increased complex V activity. Substitution of Lys 259 and Lys 480 with Arg in human ATP synthase beta, mimicking deacetylation, increased complex V activity, whereas substitution with Gln, mimicking acetylation, decreased activity. Mass spectrometry and proteomic experiments from wild-type and dsirt2 mitochondria identified the Drosophila mitochondrial acetylome and revealed dSirt2 as an important regulator of mitochondrial energy metabolism. Additionally, we unravel a ceramide-NAD(+)-sirtuin axis wherein increased ceramide, a sphingolipid known to induce stress responses, resulted in depletion of NAD(+) and consequent decrease in sirtuin activity. These results provide insight into sirtuin-mediated regulation of complex V and reveal a novel link between ceramide and Drosophila acetylome
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