613 research outputs found
Thyroid hormones correlate with field metabolic rate in ponies, Equus ferus caballus
Acknowledgments The authors thank JĂŒrgen Dörl for technical help and for taking care of the animals and Peter Thompson for technical assistance with the doubly labelled water analysis. Funding The study was supported by a grant from the German Research Foundation (DFG;GE 704/13-1).Peer reviewedPublisher PD
Seasonal changes in energy expenditure, body temperature and activity patterns in llamas (Lama glama)
The authors thank Knut Salzmann und Arne Oppermann for technical help and for taking care of the animals and Anna Stölzl for help with the administering of the ruminal unit of the telemetry system. The study was supported by a grant from the German Research Foundation (DFG) to A.R. (RI 1796/3-1).Peer reviewedPublisher PD
Selective Enzymatic Oxidation of Silanes to Silanols
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wildâtype cytochrome P450 monooxygenase (P450_(BM3) from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this nonânative activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves CâH bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native CâH hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire
Role of the Maillard Reaction in Aging of Tissue Proteins: Advanced Glycation End Product-Dependent Increase in Imidazolium Cross-Links in Human Lens Proteins
Dicarbonyl compounds such as glyoxal and methylglyoxal are reactive dicarbonyl intermediates in the nonenzymatic browning and cross-linking of proteins during the Maillard reaction. We describe here the quantification of glyoxal and methylglyoxal-derived imidazolium cross-links in tissue proteins. The imidazolium salt cross-links, glyoxal-lysine dimer (GOLD) and methylglyoxal-lysine dimer (MOLD), were measured by liquid chromatography/mass spectrometry and were present in lens protein at concentrations of 0. 02-0.2 and 0.1-0.8 mmol/mol of lysine, respectively. The lens concentrations of GOLD and MOLD correlated significantly with one another and also increased with lens age. GOLD and MOLD were present at significantly higher concentrations than the fluorescent cross-links pentosidine and dityrosine, identifying them as major Maillard reaction cross-links in lens proteins. Like the N-carboxy-alkyllysines Nepsilon-(carboxymethyl)lysine and Nepsilon-(carboxyethyl)lysine, these cross-links were also detected at lower concentrations in human skin collagen and increased with age in collagen. The presence of GOLD and MOLD in tissue proteins implicates methylglyoxal and glyoxal, either free or protein-bound, as important precursors of protein cross-links formed during Maillard reactions in vivo during aging and in disease
Spectral Decomposition of Broad-Line AGNs and Host Galaxies
Using an eigenspectrum decomposition technique, we separate the host galaxy
from the broad line active galactic nucleus (AGN) in a set of 4666 spectra from
the Sloan Digital Sky Survey (SDSS), from redshifts near zero up to about 0.75.
The decomposition technique uses separate sets of galaxy and quasar
eigenspectra to efficiently and reliably separate the AGN and host
spectroscopic components. The technique accurately reproduces the host galaxy
spectrum, its contributing fraction, and its classification. We show how the
accuracy of the decomposition depends upon S/N, host galaxy fraction, and the
galaxy class. Based on the eigencoefficients, the sample of SDSS broad-line AGN
host galaxies spans a wide range of spectral types, but the distribution
differs significantly from inactive galaxies. In particular, post-starburst
activity appears to be much more common among AGN host galaxies. The
luminosities of the hosts are much higher than expected for normal early-type
galaxies, and their colors become increasingly bluer than early-type galaxies
with increasing host luminosity. Most of the AGNs with detected hosts are
emitting at between 1% and 10% of their estimated Eddington luminosities, but
the sensitivity of the technique usually does not extend to the Eddington
limit. There are mild correlations among the AGN and host galaxy
eigencoefficients, possibly indicating a link between recent star formation and
the onset of AGN activity. The catalog of spectral reconstruction parameters is
available as an electronic table.Comment: 18 pages; accepted for publication in A
Radio Continuum Emission at 1.4 GHz from KISS Emission-Line Galaxies
We have searched the Faint Images of the Radio Sky at Twenty centimeters
(FIRST) and the NRAO VLA Sky Survey (NVSS) 1.4 GHz radio surveys for sources
that are coincident with emission-line galaxy (ELG) candidates from the KPNO
International Spectroscopic Survey (KISS). A total of 207 of the 2157 KISS ELGs
(~10%) in the first two H-alpha-selected survey lists were found to possess
radio detections in FIRST and/or NVSS. Follow-up spectra exist for all of the
radio detections, allowing us to determine the activity type (star-forming vs.
AGN) for the entire sample. We explore the properties of the radio-detected
KISS galaxies in order to gain a better insight into the nature of
radio-emitting galaxies in the local universe (z < 0.1). No dwarf galaxies were
detected, despite the large numbers of low-luminosity galaxies present in KISS,
suggesting that lower mass, lower luminosity objects do not possess strong
galaxian-scale magnetic fields. Due to the selection technique used for KISS,
our radio ELGs represent a quasi-volume-limited sample, which allows us to
develop a clearer picture of the radio galaxy population at low redshift.
Nearly 2/3rds of the KISS radio galaxies are starburst/star-forming galaxies,
which is in stark contrast to the results of flux-limited radio surveys that
are dominated by AGNs and elliptical galaxies (i.e., classic radio galaxies).
While there are many AGNs among the KISS radio galaxies, there are no objects
with large radio powers in our local volume. We derive a radio luminosity
function (RLF) for the KISS ELGs that agrees very well with previous RLFs that
adequately sample the lower-luminosity radio population.Comment: Accepted for publication in the Astronomical Journal (April 2004); 23
pages, 16 figure
A Catalogue of Morphologically Classified Galaxies from the Sloan Digital Sky Survey: North Equatorial Region
We present a catalogue of morphologically classified bright galaxies in the
north equatorial stripe (230 deg) derived from the Third Data Release of
the Sloan Digital Sky Survey (SDSS). Morphological classification is performed
by visual inspection of images in the band. The catalogue contains 2253
galaxies complete to a magnitude limit of after Galactic extinction
correction, selected from 2658 objects that are judged as extended in the
photometric catalogue in the same magnitude limit. 1866 galaxies in our
catalogue have spectroscopic information. A brief statistical analysis is
presented for the frequency of morphological types and mean colours in the
catalogue. A visual inspection of the images reveals that the rate of
interacting galaxies in the local Universe is approximately 1.5% in the
sample. A verification is made for the photometric catalogue generated
by the SDSS, especially as to its bright end completeness.Comment: Accepted for publication in Astronomical Journal. Table 2 available
at http://www.icrr.u-tokyo.ac.jp/~fukugita/MCGpaper/table2.tx
Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple
epochs, we find that the composite flux density differences in the rest frame
wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk
model where the accretion rate has changed from one epoch to the next (without
considering additional continuum emission components). The fit to the composite
residual has two free parameters: a normalizing constant and the average
characteristic temperature . In turn the characteristic temperature
is dependent on the ratio of the mass accretion rate to the square of the black
hole mass. We therefore conclude that most of the UV/optical variability may be
due to processes involving the disk, and thus that a significant fraction of
the UV/optical spectrum may come directly from the disk.Comment: 31 pages, 8 figure
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