Does the intermediate-mass black hole in LEDA 87300 (RGG 118) follow the near-quadratic Mbh-Mspheroid relation?

The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (105 < Mbh/Mo ≲ 107). How this extends into the realm of intermediate-mass black holes (102 < Mbh/Mo < 105) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. recently reported a nominal virial mass of Mbh = 5 104 Mo residing in a "spheroid" of stellar mass equal to 6.3 108 Mo. We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic Mbh-Msph,∗ relation. However, Baldassare et al. modeled the bulge and bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published "bulge" luminosity. After correcting for dust, we find that Mbulge = 0.9 108 Mo and Mbulge/Mdisk = 0.04 - which is now in accord with ratios typically found in Scd-Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40 11 km s-1) and black hole mass () and show that LEDA 87300 remains consistent with the Mbh-σ relation, and also the near-quadratic Mbh-Msph,∗ relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate-mass black holes

Arsenic Exposure Causes Global Changes in the Metalloproteome of Escherichia coli

Arsenic is a toxic metalloid with differential biological effects, depending on speciation and concentration. Trivalent arsenic (arsenite, AsIII) is more toxic at lower concentrations than the pentavalent form (arsenate, AsV). In E. coli, the proteins encoded by the arsRBC operon are the major arsenic detoxification mechanism. Our previous transcriptional analyses indicate broad changes in metal uptake and regulation upon arsenic exposure. Currently, it is not known how arsenic exposure impacts the cellular distribution of other metals. This study examines the metalloproteome of E. coli strains with and without the arsRBC operon in response to sublethal doses of AsIII and AsV. Size exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICPMS) was used to investigate the distribution of five metals (56Fe, 24Mg, 66Zn, 75As, and 63Cu) in proteins and protein complexes under native conditions. Parallel analysis by SEC-UV-Vis spectroscopy monitored the presence of protein cofactors. Together, these data reveal global changes in the metalloproteome, proteome, protein cofactors, and soluble intracellular metal pools in response to arsenic stress in E. coli. This work brings to light one outcome of metal exposure and suggests that metal toxicity on the cellular level arises from direct and indirect effects

Arsenic Exposure Causes Global Changes in the Metalloproteome of <i>Escherichia coli</i>

Arsenic is a toxic metalloid with differential biological effects, depending on speciation and concentration. Trivalent arsenic (arsenite, AsIII) is more toxic at lower concentrations than the pentavalent form (arsenate, AsV). In E. coli, the proteins encoded by the arsRBC operon are the major arsenic detoxification mechanism. Our previous transcriptional analyses indicate broad changes in metal uptake and regulation upon arsenic exposure. Currently, it is not known how arsenic exposure impacts the cellular distribution of other metals. This study examines the metalloproteome of E. coli strains with and without the arsRBC operon in response to sublethal doses of AsIII and AsV. Size exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICPMS) was used to investigate the distribution of five metals (56Fe, 24Mg, 66Zn, 75As, and 63Cu) in proteins and protein complexes under native conditions. Parallel analysis by SEC-UV-Vis spectroscopy monitored the presence of protein cofactors. Together, these data reveal global changes in the metalloproteome, proteome, protein cofactors, and soluble intracellular metal pools in response to arsenic stress in E. coli. This work brings to light one outcome of metal exposure and suggests that metal toxicity on the cellular level arises from direct and indirect effects

Joint discussion 6 neutron stars and black holes in star clusters

This article was co-authored by all invited speakers at Joint Discussion 6 on Neutron Stars and Black Holes in Star Clusters, which took place during the IAU General Assembly in Prague, Czech Republic, on August 17 and 18, 2006. Each section presents a short summary of recent developments in a key area of research, incorporating the main ideas expressed during the corresponding panel discussion at the meeting