323 research outputs found
Protein dynamics in the reductive activation of a B12-containing enzyme
B12-dependent proteins are involved in methyl transfer reactions ranging from the biosynthesis of methionine in humans to the formation of acetyl-CoA in anaerobic bacteria. During their catalytic cycle, they undergo large conformational changes to interact with various proteins. Recently, the crystal structure of the B12-containing corrinoid iron–sulfur protein (CoFeSP) in complex with its reductive activator (RACo) was determined, providing a first glimpse of how energy is transduced in the ATP-dependent reductive activation of corrinoid-containing methyltransferases. The thermodynamically uphill electron transfer from RACo to CoFeSP is accompanied by large movements of the cofactor-binding domains of CoFeSP. To refine the structure-based mechanism, we analyzed the conformational change of the B12-binding domain of CoFeSP by pulsed electron–electron double resonance and Förster resonance energy transfer spectroscopy. We show that the site-specific labels on the flexible B12-binding domain and the small subunit of CoFeSP move within 11 Å in the RACo:CoFeSP complex, consistent with the recent crystal structures. By analyzing the transient kinetics of formation and dissociation of the RACo:CoFeSP complex, we determined values of 0.75 μM–1 s–1 and 0.33 s–1 for rate constants kon and koff, respectively. Our results indicate that the large movement observed in crystals also occurs in solution and that neither the formation of the protein encounter complex nor the large movement of the B12-binding domain is rate-limiting for the ATP-dependent reductive activation of CoFeSP by RACo
Relationship between fine-mode AOD and precipitation on seasonal and interannual time scales
On seasonal and interannual time scales, weather is highly influential in aerosol variability. In this study, we investigate the relationship between fine-mode AOD (fAOD) and precipitation on these scales, in order to unravel the effect of wet weather on aerosol amount. We find with integrated satellite and ground observations that biomass burning related fAOD has a relatively greater seasonal variation than fossil fuel combustion related fAOD. It is also found that wet weather reduces biomass burning fAOD and increases fossil fuel combustion fAOD. Aerosol simulation models forced by reanalyses consistently simulate the biomass burning fAOD reduced during wet weather but only in the tropics and furthermore do not consistently increase fossil fuel combustion fAOD during wet conditions. The identified relationship between fAOD and precipitation in observations allows for seasonal predictability of fAOD, since average precipitation can be predicted a few to several months in advance due to the well-established predictability of El Niño-Southern Oscillation (ENSO). We reveal ENSO-covariant fAOD using a rotated component principal analysis of combined interannual variation of sea surface temperature, precipitation and fAOD. During the warm phase of ENSO, we find that fAOD increases over Indonesia and the eastern coastal area of China, and decreases over South Asia, the Amazon and the continental parts of China
Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic ep scattering have
been studied in the Breit frame with the ZEUS detector at HERA using an
integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in
terms of the angular separation between current-region particles within a cone
centred around the virtual photon axis. Long-range correlations between the
current and target regions have also been measured. The data support
predictions for the scaling behaviour of the angular correlations at high Q2
and for anti-correlations between the current and target regions over a large
range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations
and Monte Carlo models correctly describe the trends of the data at high Q2,
but show quantitative discrepancies. The data show differences between the
correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C
Search for n-nbar oscillation in Super-Kamiokande
A search for neutron-antineutron () oscillation was undertaken in
Super-Kamiokande using the 1489 live-day or neutron-year
exposure data. This process violates both baryon and baryon minus lepton
numbers by an absolute value of two units and is predicted by a large class of
hypothetical models where the seesaw mechanism is incorporated to explain the
observed tiny neutrino masses and the matter-antimatter asymmetry in the
Universe. No evidence for oscillation was found, the lower limit of
the lifetime for neutrons bound in O, in an analysis that included all
of the significant sources of experimental uncertainties, was determined to be
~years at the 90\% confidence level. The corresponding
lower limit for the oscillation time of free neutrons was calculated to be ~s using a theoretical value of the nuclear suppression factor of
~s and its uncertainty.Comment: 8 pages, 2 figure
Search for n-nbar oscillation in Super-Kamiokande
A search for neutron-antineutron () oscillation was undertaken in
Super-Kamiokande using the 1489 live-day or neutron-year
exposure data. This process violates both baryon and baryon minus lepton
numbers by an absolute value of two units and is predicted by a large class of
hypothetical models where the seesaw mechanism is incorporated to explain the
observed tiny neutrino masses and the matter-antimatter asymmetry in the
Universe. No evidence for oscillation was found, the lower limit of
the lifetime for neutrons bound in O, in an analysis that included all
of the significant sources of experimental uncertainties, was determined to be
~years at the 90\% confidence level. The corresponding
lower limit for the oscillation time of free neutrons was calculated to be ~s using a theoretical value of the nuclear suppression factor of
~s and its uncertainty.Comment: 8 pages, 2 figure
- …