1,724 research outputs found
Covalently bound substrate at the regulatory site triggers allosteric enzyme activation
The mechanism by which the enzyme pyruvate decarboxylase from yeast is activated allosterically has been elucidated. A total of seven three-dimensional structures of the enzyme, of enzyme variants or of enzyme complexes form two yeast species (three of them reported here for the first time) provide detailed atomic resolution snapshots along the activation coordinate. The prime event is the covalent binding of the substrate pyruvate to the side chain of cysteine 221, thus forming a thiohemiketal. This reaction causes the shift of a neighbouring amino acid, which eventually leads to the rigidification of two otherwise flexible loops, where one of the loops provides two histidine residues necessary to complete the enzymatically competent active site architecture. The structural data are complemented and supported by kinetic investigations and binding studies and provide a consistent picture of the structural changes, which occur upon enzyme activation
Photonic crystal resonator integrated in a microfluidic system
We report on a novel optofluidic system consisting of a silica-based 1D
photonic crystal, integrated planar waveguides and electrically insulated
fluidic channels. An array of pillars in a microfluidic channel designed for
electrochromatography is used as a resonator for on-column label-free
refractive index detection. The resonator was fabricated in a silicon
oxynitride platform, to support electroosmotic flow, and operated at 1.55
microns. Different aqueous solutions of ethanol with refractive indices ranging
from n = 1.3330 to 1.3616 were pumped into the column/resonator and the
transmission spectra were recorded. Linear shifts of the resonant wavelengths
yielded a maximum sensitivity of 480 nm/RIU and a minimum difference of 0.007
RIU was measured
Acoustic resonances in microfluidic chips: full-image micro-PIV experiments and numerical simulations
We show that full-image micro-PIV analysis in combination with images of
transient particle motion is a powerful tool for experimental studies of
acoustic radiation forces and acoustic streaming in microfluidic chambers under
piezo-actuation in the MHz range. The measured steady-state motion of both
large 5 um and small 1 um particles can be understood in terms of the acoustic
eigenmodes or standing ultra-sound waves in the given experimental
microsystems. This interpretation is supported by numerical solutions of the
corresponding acoustic wave equation.Comment: RevTex, 10 pages, 9 eps figures; NOTE first authors changed his name
to S. Melker Hagsater in the published versio
Cryogenic Orbital Testbed (CRYOTE) Ground Test Article, Final Report
Liquid propulsion has been used since Robert Goddard started developing a liquid oxygen (LO2) and gasoline powered rocket and fired it in 1923 (Ref. 1). In the following decades engineers settled on the combination of liquid hydrogen (LH2) and LO2 as the most efficient propellant combination for in-space travel. Due to their low temperatures (LH2 at 20 K and LO2 at 90 K), they require special handling and procedures. General Dynamics began developing LO2 and LH2 upper stages in 1956 in the form of Centaur, these efforts were soon funded by the Department of Defense in conjunction with NASA (beginning in 1958) (Ref. 2). Meanwhile NASA also worked with McDonnell Douglas to develop the SIV-B stage for the Saturn V rocket. In the subsequent years, the engineers were able to push the Centaur to up to 9 hr of orbital lifetime and the SIV-B to up to 6 hr. Due to venting the resultant boil-off from the high heat loads through the foam insulation on the upper stages, both vehicles remained in a settled configuration throughout the flights, thus the two phases of propellant (liquid and vapor) were separated at a known location. The one exception to this were the Titan/Centaur missions, which thanks to the lower boil-off using three layers of multilayer insulation (MLI), were able to coast unsettled for up to 5.25 hr during direct geosynchronous orbit insertion missions. In the years since there has been a continuous effort to extend the life of these upper stages from hours to days or even months
Isolation of Salmonella spp. and bacteriophage active against Salmonella spp. from commercial swine
Bacteriophage are viruses that prey on bacteria and may be a potential strategy to reduce foodborne pathogemc bactena in the gastromtestlnal tract of food animals Phages are fairly common in the gastrointestinal microbial ecosystem of mammals, but the incidence is unknown. If phage are to be an intervention strategy, we must understand their role in the microbial ecology of the gut. From a regulatory perspective, knowing incidence of phage is crucial. Therefore the current study was designed to determine the incidence of phage active against Salmonella spp in the feces of commercial finishing swine in the United States. Fecal samples (n=60) were collected from each of six commercial swine finishing operations. Samples were collected from 10 randomly selected pens throughout each operation. Total number of fecal samples collected in this study was n=360 Salmonella spp were found in 66% of the fecal samples Salmonella spp. were isolated from only 2 farms and the serotypes represented were Schwarzengrund, Anatum, Ohio and Heidelberg Bacteriophages were isolated from fecal sample through 2 parallel methods, 1) initlal enrichment in Salmonella Typhimunum, or 2) initial ennchment in E. colt B (a strain very sensitive to phages), followed by direct spot-testing against Salmonella Typhimurium Bacteriophages active against Salmonella Typhimunum were isolated from 1.1% 4/360) of the individual fecal samples when initially enriched in Salmonella Typhimurium, but E coli S-killing phages were 1solated from 43.8% (158/360) of the fecal samples but only 2 of these Isolates were capable of k1ll1ng Salmonella Typhimunum. Our results mdicate that bactenophage capable of killing Salmonella Typh1murium are fairly w1despread across commercial swine production facilities but may be present at relatively low populat1ons These results md1cate that phage (predator) populations may vary along w1th Salmonella (prey) populations and that phage could potentially be used as a food safety pathogen reduction strategy
Experimental study of the atmospheric neutrino backgrounds for proton decay to positron and neutral pion searches in water Cherenkov detectors
The atmospheric neutrino background for proton decay to positron and neutral
pion in ring imaging water Cherenkov detectors is studied with an artificial
accelerator neutrino beam for the first time. In total, about 314,000 neutrino
events corresponding to about 10 megaton-years of atmospheric neutrino
interactions were collected by a 1,000 ton water Cherenkov detector (KT). The
KT charged-current single neutral pion production data are well reproduced by
simulation programs of neutrino and secondary hadronic interactions used in the
Super-Kamiokande (SK) proton decay search. The obtained proton to positron and
neutral pion background rate by the KT data for SK from the atmospheric
neutrinos whose energies are below 3 GeV is about two per megaton-year. This
result is also relevant to possible future, megaton-scale water Cherenkov
detectors.Comment: 13 pages, 16 figure
Search for coherent charged pion production in neutrino-carbon interactions
We report the result from a search for charged-current coherent pion
production induced by muon neutrinos with a mean energy of 1.3 GeV. The data
are collected with a fully active scintillator detector in the K2K
long-baseline neutrino oscillation experiment. No evidence for coherent pion
production is observed and an upper limit of is set on
the cross section ratio of coherent pion production to the total
charged-current interaction at 90% confidence level. This is the first
experimental limit for coherent charged pion production in the energy region of
a few GeV.Comment: 5 pages, 4 figure
The phage therapy paradigm: prêt-à -porter or sur-mesure?
The present opinion is the result of discussions on the future of
phage therapy (personalized or large-scale uniform therapy?)
during the first International Congress on Viruses of Microbes,
held at the Institut Pasteur in Paris on June 21–25, 2010
Measurement of single charged pion production in the charged-current interactions of neutrinos in a 1.3 GeV wide band beam
Single charged pion production in charged-current muon neutrino interactions
with carbon is studied using data collected in the K2K long-baseline neutrino
experiment. The mean energy of the incident muon neutrinos is 1.3 GeV. The data
used in this analysis are mainly from a fully active scintillator detector,
SciBar. The cross section for single production in the resonance
region ( GeV/) relative to the charged-current quasi-elastic cross
section is found to be 0.734 . The energy-dependent cross
section ratio is also measured. The results are consistent with a previous
experiment and the prediction of our model.Comment: 15 pages, 12 figures, 7 tables. Uses revtex4. Minor revisions to
match version accepted for publication in Physical Review
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