1,346 research outputs found
Use of a distant reporter group as evidence for a conformational change in a sensory receptor
A highly sensitive method for demonstrating ligand-induced conformational changes in protein molecules in solution is described. The method utilizes an environmentally sensitive reporter group that is known to be distant from the active site. In the present application a conformational change is demonstrated in the galactose receptor of Salmonella typhimurium, involved in bacterial sensing and transport, by means of an extrinsic fluorophore, 5-iodoacetamidofluorescein, attached at a single methionine residue, and the intrinsic tryptophan fluorophore. Binding of the ligand galactose perturbs the microenvironment of both the fluorescein and tryptophan, as shown by both spectral and potassium iodide quenching changes. The distance between the two dyes is established by fluorescence energy transfer methods to be 41 ± 10 angstrom. Since only one molecule of galactose binds per molecule of receptor and since the galactose molecule is only about 5 angstrom in length, changes at one of these sites reflect the result of an indirect effect. Hence, there must be a ligand-induced conformational change that is propagated a minimum of 30 angstrom through the receptor molecule
Rocket and FUSE Observations of IC 405: Differential Extinction and Fluorescent Molecular Hydrogen
We present far-ultraviolet spectroscopy of the emission/reflection nebula IC
405 obtained by a rocket-borne long-slit spectrograph and the Far Ultraviolet
Spectroscopic Explorer. Both data sets show a rise in the ratio of the nebular
surface brightness to stellar flux (S/F_*) of approximately two orders of
magnitude towards the blue end of the far-UV bandpass. Scattering models using
simple dust geometries fail to reproduce the observed S/F_* for realistic grain
properties. The high spectral resolution of the FUSE data reveals a rich
fluorescent molecular hydrogen spectrum ~1000" north of the star that is
clearly distinguished from the steady blue continuum. The S/F_* remains roughly
constant at all nebular pointings, showing that fluorescent molecular hydrogen
is not the dominant cause for the blue rise. We discuss three possible
mechanisms for the ``Blue Dust'': differential extinction of the dominant star
(HD 34078), unusual dust grain properties, and emission from nebular dust. We
conclude that uncertainties in the nebular geometry and the degree of dust
clumping are most likely responsible for the blue rise. As an interesting
consequence of this result, we consider how IC 405 would appear in a spatially
unresolved observation. If IC 405 was observed with a spatial resolution of
less than 0.4 pc, for example, an observer would infer a far-UV flux that was
2.5 times the true value, giving the appearance of a stellar continuum that was
less extinguished than radiation from the surrounding nebula, an effect that is
reminiscent of the observed ultraviolet properties of starburst galaxies.Comment: 8 pages, 9 figures, using emulateapj, ApJ - accepte
Targeted colonic release formulations of mesalazine - A clinical pharmaco-scintigraphic proof-of-concept study in healthy subjects and patients with mildly active ulcerative colitis.
Colonic targeting of orally applied therapeutic drugs remains a challenge. Tablet coatings relying on gastrointestinal pH and colonic bacterial enzymes as triggers in association with an inner alkaline layer are expected to improve targeting efficiency. Mesalazine release from three differently coated tablets labelled with 1 MBq 153Sm was characterised in a single centre, open-label, parallel group study in nineteen healthy subjects and seven patients with mildly active ulcerative colitis. Two semi-organic and one aqueous-based outer coating with different ratios of enteric polymer and resistant starch were tested. All coatings showed comparable release lagtimes in biorelevant dissolution media and were not affected by neutron-activation of the samarium tracer. Mesalazine pharmacokinetics and gamma scintigraphy were used to characterise drug release, anatomical site of tablet disintegration and gastrointestinal transit. Initial tablet disintegration occurred at the ileo-caecal junction or beyond in 92% of the subjects Time to initial tablet disintegration was inversely correlated with maximal plasma concentrations and systemic mesalazine exposure. Although high inter-subject variability precluded detection of differences between solvent types and different enteric polymer to polysaccharide ratios, the dual pH and enzymatic triggered release system in combination with an inner alkaline layer promoted mesalazine release at the target site with high accuracy
East Asian audio-visual collaboration and the global expansion of Chinese media
This article investigates the significant re-orientation of audio-visual production in East Asia over the last few years brought about by the rise of China, beginning with the proposition that unprecedented change is occurring in East Asian media production. While the 'Sinophone world' has been the locus of critical analysis in the past, all eyes are now focused on China. Flows of knowledge, expertise and content are becoming significant in this mediascape, yet this dimension has been overlooked by most scholarship in the field. Conceptual and theoretical frameworks based on cross-border consumption of East Asian content require urgent revision. This article shows how media collaborations are changing global media practice and East Asian media flows through a variety of contemporary international collaborations, as well as relevant policy frameworks that impact, positively or negatively, productions by international partners working in film, television and online and mobile video content
Male Competition Reverses Female Preference For Male Chemical Cues
Females must choose among potential mates with different phenotypes in a variety of social contexts. Many male traits are inherent and unchanging, but others are labile to social context. Competition, for example, can cause physiological changes that reflect recent wins and losses that fluctuate throughout time. We may expect females to respond differently to males depending on the outcome of their most recent fight. In Bolitotherus cornutus (forked fungus beetles), males compete for access to females, but copulation requires female cooperation. In this study, we use behavioral trials to determine whether females use chemical cues to differentiate between males and whether the outcome of recent male competition alters female preference. We measured female association time with chemical cues of two sizeâmatched males both before and after maleâmale competition. Females in our study preferred to associate with future losers before males interacted, but changed their preference for realized winners following male competitive interactions. Our study provides the first evidence of change in female preference based solely on the outcome of maleâmale competition
Fluorescent Molecular Hydrogen Emission in IC 63: FUSE, HUT, and Rocket Observations
We present far-ultraviolet observations of IC 63, an emission/reflection
nebula illuminated by the B0.5IV star gamma Cassiopeia, located 1.3 pc from the
nebula. Molecular hydrogen fluorescence was detected first in IC 63 by IUE and
later at shorter wavelengths by ORFEUS. Here we present Far Ultraviolet
Spectroscopic Explorer (FUSE) observations towards three locations in the
nebula, complemented by Hopkins Ultraviolet Telescope (HUT) data on the central
nebular position. In addition, we present a sounding rocket calibration of a
FUSE spectrum of gamma Cas. Molecular hydrogen fluorescence is detected in all
three FUSE pointings. The intensity of this emission as well as the
contributions from other species are seen to vary with position. The absolute
flux calibration of the sounding rocket data allows us to reliably predict the
radiation field incident on IC 63. We use these data to test models of the
fluorescent process. Our modeling resolves the perceived discrepancy between
the existing ultraviolet observations and achieves a satisfactory agreement
with the H_2 rotational structure observed with FUSE.Comment: 7 pages, 6 figures, using emulateapj. Accepted by Ap
Advanced Camera for Surveys Observations of Young Star Clusters in the Interacting Galaxy UGC 10214
We present the first Advanced Camera for Surveys (ACS) observations of young
star clusters in the colliding/merging galaxy UGC 10214. The observations were
made as part of the Early Release Observation (ERO) program for the newly
installed ACS during service mission SM3B for the Hubble Space Telescope (HST).
Many young star clusters can be identified in the tails of UGC 10214, with ages
ranging from ~3 Myr to 10 Myr. The extreme blue V-I (F606W-F814W) colors of the
star clusters found in the tail of UGC 10214 can only be explained if strong
emission lines are included with a young stellar population. This has been
confirmed by our Keck spectroscopy of some of these bright blue stellar knots.
The most luminous and largest of these blue knots has an absolute magnitude of
M_V = -14.45, with a half-light radius of 161 pc, and if it is a single star
cluster, would qualify as a super star cluster (SSC). Alternatively, it could
be a superposition of multiple scaled OB associations or clusters. With an
estimated age of ~ 4-5 Myr, its derived mass is < 1.3 x 10^6 solar masses. Thus
the young stellar knot is unbound and will not evolve into a normal globular
cluster. The bright blue clusters and associations are much younger than the
dynamical age of the tail, providing strong evidence that star formation occurs
in the tail long after it was ejected. UGC 10214 provides a nearby example of
processes that contributed to the formation of halos and intra-cluster media in
the distant and younger Universe.Comment: 6 pages with embedded figures, ApJ in pres
Discovery of Globular Clusters in the Proto-Spiral NGC2915: Implications for Hierarchical Galaxy Evolution
We have discovered three globular clusters beyond the Holmberg radius in
Hubble Space Telescope Advanced Camera for Surveys images of the gas-rich dark
matter dominated blue compact dwarf galaxy NGC2915. The clusters, all of which
start to resolve into stars, have M_{V606} = -8.9 to -9.8 mag, significantly
brighter than the peak of the luminosity function of Milky Way globular
clusters. Their colors suggest a metallicity [Fe/H] ~ -1.9 dex, typical of
metal-poor Galactic globular clusters. The specific frequency of clusters is at
a minimum normal, compared to spiral galaxies. However, since only a small
portion of the system has been surveyed it is more likely that the luminosity
and mass normalized cluster content is higher, like that seen in elliptical
galaxies and galaxy clusters. This suggests that NGC2915 resembles a key phase
in the early hierarchical assembly of galaxies - the epoch when much of the old
stellar population has formed, but little of the stellar disk. Depending on the
subsequent interaction history, such systems could go on to build-up larger
elliptical galaxies, evolve into normal spirals, or in rare circumstances
remain suspended in their development to become systems like NGC2915.Comment: ApJ Letters accepted; 6 pages, 2 figures, 3 table
Star Formation at z~6: i-dropouts in the ACS GTO fields
Using an i-z dropout criterion, we determine the space density of z~6
galaxies from two deep ACS GTO fields with deep optical-IR imaging. A total of
23 objects are found over 46 arcmin^2, or ~0.5 objects/arcmin^2 down to z~27.3
(6 sigma; all AB mag) (including one probable z~6 AGN). Combining deep ISAAC
data for our RDCS1252-2927 field (J~25.7 and Ks~25.0 (5 sigma)) and NICMOS data
for the HDF North (JH~27.3 (5 sigma)), we verify that these dropouts have flat
spectral slopes. i-dropouts in our sample range in luminosity from ~1.5 L*
(z~25.6) to ~0.3 L* (z~27.3) with the exception of one very bright candidate at
z~24.2. The half-light radii vary from 0.09" to 0.29", or 0.5 kpc to 1.7 kpc.
We derive the z~6 rest-frame UV luminosity density using three different
procedures, each utilizing simulations based on a CDF South V dropout sample.
First, we compare our findings with a no-evolution projection of this V-dropout
sample. We find 23+/-25% more i-dropouts than we predict. Adopting previous
results to z~5, this works out to a 20+/-29% drop in the luminosity density
from z~3 to z~6. Second, we use these same V-dropout simulations to derive a
selection function for our i-dropout sample and compute the UV-luminosity
density (7.2+/-2.5 x 10^25 ergs/s/Hz/Mpc^3 down to z~27). We find a 39+/-21%
drop over the same redshift range. This is our preferred value and suggests a
star formation rate of 0.0090+/-0.0031 M_sol/yr/Mpc^3 to z~27, or ~0.036+/-
0.012 M_sol/yr/Mpc^3 extrapolating the LF to the faint limit. Third, we follow
a very similar procedure, but assume no incompleteness, finding a luminosity
density which is ~2-3X lower. This final estimate constitutes a lower limit.
All three estimates are within the canonical range of luminosity densities
necessary for reionization of the universe at this epoch. (abridged)Comment: 36 pages, 13 figures, 2 tables, accepted for publication in ApJ,
postscript version with high-resolution figures can be downloaded at
http://www.ucolick.org/~bouwens/idropout.p
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