586 research outputs found
Characterisation of two alcohol acyltransferases from kiwifruit (Actinidia spp.) reveals distinct substrate preferences.
Volatile esters are key compounds of kiwifruit flavour and are formed by alcohol acyltransferases that belong to the BAHD acyltransferase superfamily. Quantitative RT-PCR was used to screen kiwifruitderived expressed sequence tags with proposed acyltransferase function in order to select ripeningspecific sequences and test their involvement in alcohol acylation. The screening criterion was for at least 10-fold increased transcript accumulation in ripe compared with unripe kiwifruit and in response to ethylene. Recombinant expression in yeast revealed alcohol acyltransferase activity for Actinidia-derived AT1, AT16 and the phylogenetically distinct AT9, using various alcohol and acyl-CoA substrates. Functional characterisation of AT16 and AT9 demonstrated striking differences in their substrate preferences and apparent catalytic efficiencies ðV0 max K�1 m Þ. Thus revealing benzoyl-CoA:alcohol O-acyltransferase activity for AT16 and acetyl-CoA:alcohol O-acyltransferase activity for AT9. Both kiwifruit-derived enzymes displayed higher reaction rates with butanol compared with ethanol, even though ethanol is the main alcohol in ripe fruit. Since ethyl acetate and ethyl benzoate are major esters in ripe kiwifruit, we suggest that fruit characteristic volatile profiles result from a combination of substrate availability and specificity of individual alcohol acyltransferases
Dynamics of the magnetic and structural a -> e phase transition in Iron
We have studied the high-pressure iron bcc to hcp phase transition by
simultaneous X-ray Magnetic Circular Dichroism (XMCD) and X-ray Absorption
Spectroscopy (XAS) with an X-ray dispersive spectrometer. The combination of
the two techniques allows us to obtain simultaneously information on both the
structure and the magnetic state of Iron under pressure. The magnetic and
structural transitions simultaneously observed are sharp. Both are of first
order in agreement with theoretical prediction. The pressure domain of the
transition observed (2.4 0.2 GPa) is narrower than that usually cited in
the literature (8 GPa). Our data indicate that the magnetic transition slightly
precedes the structural one, suggesting that the origin of the instability of
the bcc phase in iron with increasing pressure is to be attributed to the
effect of pressure on magnetism as predicted by spin-polarized full potential
total energy calculations
Disk Heating, Galactoseismology, and the Formation of Stellar Halos
Deep photometric surveys of the Milky Way have revealed diffuse structures
encircling our Galaxy far beyond the "classical" limits of the stellar disk.
This paper reviews results from our own and other observational programs, which
together suggest that, despite their extreme positions, the stars in these
structures were formed in our Galactic disk. Mounting evidence from recent
observations and simulations implies kinematic connections between several of
these distinct structures. This suggests the existence of collective disk
oscillations that can plausibly be traced all the way to asymmetries seen in
the stellar velocity distribution around the Sun. There are multiple
interesting implications of these findings: they promise new perspectives on
the process of disk heating, they provide direct evidence for a stellar halo
formation mechanism in addition to the accretion and disruption of satellite
galaxies, and, they motivate searches of current and near-future surveys to
trace these oscillations across the Galaxy. Such maps could be used as
dynamical diagnostics in the emerging field of "Galactoseismology", which
promises to model the history of interactions between the Milky Way and its
entourage of satellites, as well examine the density of our dark matter halo.
As sensitivity to very low surface brightness features around external galaxies
increases, many more examples of such disk oscillations will likely be
identified. Statistical samples of such features not only encode detailed
information about interaction rates and mergers, but also about long
sought-after dark matter halo densities and shapes. Models for the Milky Way's
own Galactoseismic history will therefore serve as a critical foundation for
studying the weak dynamical interactions of galaxies across the universe.Comment: 20 pages, 5 figures, accepted in for publication in a special edition
of the journal "Galaxies", reporting the proceedings of the conference "On
the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador,
March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope
Sleep‐disordered breathing is common among term and near term infants in the NICU
ObjectiveAmong older infants and children, sleep‐disordered breathing (SDB) has negative neurocognitive consequences. We evaluated the frequency and potential impact of SDB among newborns who require intensive care.Study DesignTerm and near‐term newborns at risk for seizures underwent 12‐h attended polysomnography in the neonatal intensive care unit (NICU). Bayley Scales of Infant Development, third edition (Bayley‐III) were administered at 18‐22 months.ResultThe 48 newborns (EGA 39.3 ± 1.6) had a median pediatric apnea‐hypopnea index (AHI) of 10.1 (3.3‐18.5) and most events were central (vs obstructive). Maternal and prenatal factors were not associated with AHI. Moreover, neonatal PSG results were not associated with Bayley‐III scores (P > 0.05).ConclusionSDB is common among term and near‐term newborns at risk for seizures. Follow‐up at ages when more nuanced testing can be performed may be necessary to establish whether neonatal SDB is associated with long‐term neurodevelopmental disability.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149248/1/ppul24266.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149248/2/ppul24266_am.pd
GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
The Milky Way stellar halo contains relics of ancient mergers that tell the
story of our Galaxy's formation. Some of them are identified due to their
similarity in energy, actions and chemistry, referred to as the "chemodynamical
space", and are often attributed to distinct merger events. It is also known
that our Galaxy went through a significant merger event that shaped the local
stellar halo during its first Gyr. Previous studies using -body only and
cosmological hydrodynamical simulations have shown that such single massive
merger can produce several "signatures" in the chemodynamical space, which can
potentially be misinterpreted as distinct merger events. Motivated by these, in
this work we use a subset of the GASTRO, library which consists of several
SPH+-body models of single accretion event in a Milky Way-like galaxy. Here,
we study models with orbital properties similar to the main merger event of our
Galaxy and explore the implications to known stellar halo substructures. We
find that: supernova feedback efficiency influences the satellite's
structure and orbital evolution, resulting in distinct chemodynamical features
for models with the same initial conditions, very retrograde high energy
stars are the most metal-poor of the accreted dwarf galaxy and could be
misinterpreted as a distinct merger the most bound stars are more
metal-rich in our models, the opposite of what is observed in the Milky Way,
suggesting a secondary massive merger, and finally our models can
reconcile other known substructures to an unique progenitor.Comment: Published in Ap
Snails Across Scales: Local and Global Phase-Mixing Structures as Probes of the Past and Future Milky Way
Signatures of vertical disequilibrium have been observed across the Milky
Way's disk. These signatures manifest locally as unmixed phase-spirals in
-- space ("snails-in-phase") and globally as nonzero mean and
which wraps around as a physical spiral across the -- plane
("snails-in-space"). We explore the connection between these local and global
spirals through the example of a satellite perturbing a test-particle Milky Way
(MW)-like disk. We anticipate our results to broadly apply to any vertical
perturbation.
Using a -- asymmetry metric we demonstrate that in test-particle
simulations: (a) multiple local phase-spiral morphologies appear when stars are
binned by azimuthal action , excited by a single event (in our case, a
satellite disk-crossing); (b) these distinct phase-spirals are traced back to
distinct disk locations; and (c) they are excited at distinct times. Thus,
local phase-spirals offer a global view of the MW's perturbation history from
multiple perspectives.
Using a toy model for a Sagittarius (Sgr)-like satellite crossing the disk,
we show that the full interaction takes place on timescales comparable to
orbital periods of disk stars within kpc. Hence such
perturbations have widespread influence which peaks in distinct regions of the
disk at different times.
This leads us to examine the ongoing MW-Sgr interaction. While Sgr has not
yet crossed the disk (currently, kpc, km/s), we demonstrate that the peak of the impact has already passed.
Sgr's pull over the past 150 Myr creates a global signature with
amplitude , which might be detectable in future spectroscopic
surveys
Interaction of Streptavidin-Based Peptide-MHC Oligomers (Tetramers) with Cell-Surface T Cell Receptors
he binding of oligomeric peptide–MHC (pMHC) complexes to cell surface TCR can be considered to approximate TCR–pMHC interactions at cell-cell interfaces. In this study, we analyzed the equilibrium binding of streptavidin-based pMHC oligomers (tetramers) and their dissociation kinetics from CD8[superscript pos] T cells from 2C-TCR transgenic mice and from T cell hybridomas that expressed the 2C TCR or a high-affinity mutant (m33) of this TCR. Our results show that the tetramers did not come close to saturating cell-surface TCR (binding only 10–30% of cell-surface receptors), as is generally assumed in deriving affinity values (K[subscript D]), in part because of dissociative losses from tetramer-stained cells. Guided by a kinetic model, the oligomer dissociation rate and equilibrium constants were seen to depend not only on monovalent association and dissociation rates (k[subscript off] and k[subscript on]), but also on a multivalent association rate (μ) and TCR cell-surface density. Our results suggest that dissociation rates could account for the recently described surprisingly high frequency of tetramer-negative, functionally competent T cells in some T cell responses.National Institutes of Health (U.S.) (Grant P01 CA097296)National Institutes of Health (U.S.) (Grant R01 GM55767)National Institutes of Health (U.S.) (Grant PO1-AI071195)National Institutes of Health (U.S.). Pioneer Awar
The Prince and the Pauper: Evidence for the early high-redshift formation of the Galactic -poor disc population
Context. The presence of [/Fe]-[Fe/H] bi-modality in the Milky Way
disc has animated the Galactic archaeology community since more than two
decades. Aims. Our goal is to investigate the chemical, temporal, and
kinematical structure of the Galactic discs using abundances, kinematics, and
ages derived self-consistently with the new Bayesian framework SAPP. Methods.
We employ the public Gaia-ESO spectra, as well as Gaia EDR3 astrometry and
photometry. Stellar parameters and chemical abundances are determined for 13
426 stars using NLTE models of synthetic spectra. Ages are derived for a
sub-sample of 2 898 stars, including subgiants and main-sequence stars. The
sample probes a large range of Galactocentric radii, 3 to 12 kpc, and
extends out of the disc plane to 2 kpc. Results. Our new data confirm the
known bi-modality in the [Fe/H] - [/Fe] space, which is often viewed as
the manifestation of the chemical thin and thick discs. The over-densities
significantly overlap in metallicity, age, and kinematics, and none of these is
a sufficient criterion for distinguishing between the two disc populations.
Different from previous studies, we find that the -poor disc population
has a very extended [Fe/H] distribution and contains 20 old stars
with ages of up to 11 Gyr. Conclusions. Our results suggest that the
Galactic thin disc was in place early, at look-back times corresponding to
redshifts z 2 or more. At ages 9 to 11 Gyr, the two disc
structures shared a period of co-evolution. Our data can be understood within
the clumpy disc formation scenario that does not require a pre-existing thick
disc to initiate a formation of the thin disc. We anticipate that a similar
evolution can be realised in cosmological simulations of galaxy formation.Comment: 14 pages, 10 figures, re-submitted to A&
Impact of hands‐on care on infant sleep in the neonatal intensive care unit
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135460/1/ppul23513_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135460/2/ppul23513.pd
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