Metal Ion Selectivity of the Vanadium(V)-Reductase Vanabin2

In a previous study, Vanabin2, a member of a family of V(IV)-binding proteins, or Vanabins, was shown to act as a V(V)-reductase. The current study assesses the ability of Vanabin2 to reduce various transition metal ions in vitro. An NADPH-coupled oxidation assay yielded no evidence of reduction activity with the hexavalent transition metal anions, MoVIO42- and WVIO42-, or with three divalent cations, Mn(II), Ni(II), and Co(II). Although Cu(II) is readily reduced by glutathione and is gradually oxidized in air, this process was not affected by the presence of Vanabin2. In the experiments conducted thus far, Vanabin2 acts only as a V(V)-reductase. This high selectivity may account for the metal ion selectivity of vanadium accumulation in ascidians

Infusion of angiotensin II reduces loss of glomerular capillary area in the early phase of anti-Thy-1.1 nephritis possibly via regulating angiogenesis-associated factors

Infusion of angiotensin II reduces loss of glomerular capillary area in the early phase of anti-Thy-1.1 nephritis possibly via regulating angiogenesis-associated factors.BackgroundAlthough angiotensin II (Ang II) is involved in the progression of renal diseases, infusion of Ang II was reported to surprisingly ameliorate the early phase of anti-Thy-1.1 nephritis (Wenzel et al,Kidney Int 61:1020, 2002). Considering the known proangiogenic effect of Ang II and that angiogenic glomerular capillary repair is required for the recovery of damaged glomeruli in rat anti-Thy-1.1 nephritis, we hypothesized that Ang II infusion starting prior to the initiation of nephritis may induce the expression of angiogenic growth factors such as vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), resulting in the increased glomerular capillary area in the early phase.MethodsAng II was infused (170ng/min) in rats, and 5 days later, nephritis was induced by the administration of monoclonal 1-22-3 antibodies. Ang II type 1 or type 2 receptor antagonist (AT1R or AT2R, respectively) (losartan or PD123319, respectively) was coadministered.ResultsAng II infusion affected on neither the deposition of Ig nor mesangiolysis in the initial phase, and resulted in the aggravation of creatinine clearance at day 14 and 35 after initiating anti-Thy-1.1 nephritis. Histologic alterations were ameliorated accompanied by reduced loss in rat endothelial cell antigen (RECA)-1(+) endothelial area in Ang II-infused nephritic rats on day 6 and 14 as compared to control nephritic group, and nephritic alterations were mostly resolved on day 35 in both groups. At the early stage (day 6), glomerular expression of VEGF and receptors flk-1 and flt-1 as well as Ang-1, and receptor Tie2 were increased, and glomerular monocyte infiltration and the expression of angiopoietin-2 (Ang-2), a natural antagonist of Ang-1, were reduced. Both Ang II receptors were involved in the regulation of angiogenic factors and receptors.ConclusionThese results demonstrate that infusion of exogenous Ang II starting prior to the induction of nephritis activates VEGF and Ang-1 signaling regulated via both Ang II receptors, potentially leading to the accelerated recovery of injured glomerular endothelial cells in the early phase of anti-Thy-1.1 nephritis. Increased expression of VEGF and Ang-1 on podocytes further suggests the crucial association of endothelial cells and podocytes in maintaining proper glomerular capillary structures

Outburst of LS V+44 17 Observed by MAXI and RXTE, and Discovery of a Dip Structure in the Pulse Profile

We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar LS V +44 17/RX J0440.9+4431, and the discovery of an absorption dip structure in the pulse profile. An outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of the transient activity of LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of the follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile which was clearer in the lower energy bands. The pulse-phase-averaged energy spectra in the 3$-$100 keV band can be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron K$\alpha$ emission line is also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in the subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column.Comment: 18 pages, 7 figures, accepted for publication in PAS

Long-term Monitoring of the Black Hole Binary GX 339-4 in the High/Soft State during the 2010 Outburst with MAXI/GSC

We present the results of monitoring the Galactic black hole candidate GX 339-4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC) in the high/soft state during the outburst in 2010. All the spectra throughout the 8-month period are well reproduced with a model consisting of multi-color disk (MCD) emission and its Comptonization component, whose fraction is <= 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at R_in = 61 +/- 2 km for the inclination angle of i = 46 deg and the distance of d=8 kpc. This R_in value is consistent with those of the past measurements with Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be M = 6.8 +/- 0.2 M_sun for i = 46 deg and d = 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtain the mass constraint of 4.3 M_sun < M < 13.3 M_sun for the allowed range of d = 6-15 kpc and i < 60 deg. We also discuss the spin parameter of the black hole in GX 339-4 by applying relativistic accretion disk models to the Swift/XRT data.Comment: 9 pages, 8 figures, accepted for publication in PASJ (Suzaku+MAXI special issue

A Spectral Study of the Black Hole Candidate XTE J1752-223 in the High/Soft State with MAXI, Suzaku and Swift

We report on the X-ray spectral analysis of the black hole candidate XTE\ J1752--223 in the 2009--2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work complementarily. As already reported by Nakahira et al. (2010) MAXI monitored the source continuously throughout the entire outburst for about eight months. All the MAXI/GSC energy spectra in the high/soft state lasting for 2 months are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from $\sim$0.7 keV to $\sim$0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at $\sim$41 $D_{3.5}(\cos{\it i})^{-1/2}$ km, where $D_{3.5}$ is the source distance in units of 3.5 kpc and $i$ the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggests a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51$\pm$0.28 $M_{\odot}$ $D_{3.5}(\cos{\it i})^{-1/2}$, where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49$^{\circ}$ as suggested from the radio monitoring of transient jets and the soft-to-hard transition in 2010 April occurred at 1--4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1--55 $M_{\odot}$ and 2.3--22 {\rm kpc}, respectively. This confirms that the compact object in XTE J1752--223 is a black hole.Comment: 12 pages including 7 figures and 4 tables, accepted for publication in PAS