1,293 research outputs found
SIRT1 and SIRT3 deacetylate homologous substrates: AceCS1,2 and HMGCS1,2.
SIRT1 and SIRT3 are NAD+-dependent protein deacetylases that are evolutionarily conserved across mammals. These proteins are located in the cytoplasm/nucleus and mitochondria, respectively. Previous reports demonstrated that human SIRT1 deacetylates Acetyl-CoA Synthase 1 (AceCS1) in the cytoplasm, whereas SIRT3 deacetylates the homologous Acetyl-CoA Synthase 2 (AceCS2) in the mitochondria. We recently showed that 3-hydroxy-3-methylglutaryl CoA synthase 2 (HMGCS2) is deacetylated by SIRT3 in mitochondria, and we demonstrate here that SIRT1 deacetylates the homologous 3-hydroxy-3-methylglutaryl CoA synthase 1 (HMGCS1) in the cytoplasm. This novel pattern of substrate homology between cytoplasmic SIRT1 and mitochondrial SIRT3 suggests that considering evolutionary relationships between the sirtuins and their substrates may help to identify and understand the functions and interactions of this gene family. In this perspective, we take a first step by characterizing the evolutionary history of the sirtuins and these substrate families
Unique Conformation of Rh(i) Pillar Complexes Immobilized on Taeniolite
Rhodium pillar complex with chiral diamine ligands, Rh-Cn-(-)-CHDA, were synthesized and intercalated with various loading amounts in the range of 19 - 26% CEC, Cation Exchange Capacity (CEC) into Lithium Taeniolite (LiTN). These pillared catalysts (Rh-Cn-(-)-CHDA/TN) were characterized by XRD, elementary analysis, and FT-IR. Results of XRD analysis showed that the clearance space of the catalyst interlayer increased proportionally with the alkyl chain length of the ligand with the slope of 0.14 nm/CH2
Superconductor-insulator quantum phase transition in a single Josephson junction
The superconductor-to-insulator quantum phase transition in resistively
shunted Josephson junctions is investigated by means of path-integral Monte
Carlo simulations. This numerical technique allows us to directly access the
(previously unexplored) regime of the Josephson-to-charging energy ratios
E_J/E_C of order one. Our results unambiguously support an earlier theoretical
conjecture, based on renormalization-group calculations, that at T -> 0 the
dissipative phase transition occurs at a universal value of the shunt
resistance R_S = h/4e^2 for all values E_J/E_C. On the other hand,
finite-temperature effects are shown to turn this phase transition into a
crossover, which position depends significantly on E_J/E_C, as well as on the
dissipation strength and on temperature. The latter effect needs to be taken
into account in order to reconcile earlier theoretical predictions with recent
experimental results.Comment: 7 pages, 6 figure
Investigation of Dynamics of Self-Similarly Evolving Magnetic Clouds
Magnetic clouds (MCs) are "magnetized plasma clouds" moving in the solar
wind. MCs transport magnetic flux and helicity away from the Sun. These
structures are not stationary but feature temporal evolution. Commonly,
simplified MC models are considered. The goal of the present study is to
investigate the dynamics of more general, radially expanding MCs. They are
considered as cylindrically symmetric magnetic structures with low plasma
{\beta}. In order to study MC`evolution the self-similar approach method and a
numerical approach are used. It is shown that the forces are balanced in the
considered self-similarly evolving, cylindrically symmetric magnetic
structures. Explicit analytical expressions for magnetic field, plasma
velocity, density and pressure within MCs are derived. These solutions are
characterized by conserved values of magnetic flux and helicity. We also
investigate the dynamics of self-similarly evolving MCs by means of the
numerical code "Graale". In addition, their expansion in a medium with higher
density and higher plasma {\beta} is studied. It is shown that the physical
parameters of the MCs maintain their self-similar character throughout their
evolution. Conclusions. A comparison of the different self-similar and
numerical solutions allows us to conclude that the evolving MCs are quite
adequately described by our self-similar solutions - they retain their
self-similar, coherent nature for quite a long time and over large distances
from the Sun
Dynamics of solar wind protons reflected by the Moon
Solar system bodies that lack a significant atmosphere and significant
internal magnetic fields, such as the Moon and asteroids, have been considered
as passive absorbers of the solar wind. However, ion observations near the Moon
by the SELENE spacecraft show that a fraction of the impacting solar wind
protons are reflected by the surface of the Moon. Using new observations of the
velocity spectrum of these reflected protons by the SARA experiment on-board
the Chandrayaan-1 spacecraft at the Moon, we show by modeling that the
reflection of solar wind protons will affect the global plasma environment.
These global perturbations of the ion fluxes and the magnetic fields will
depend on microscopic properties of the object's reflecting surface. This solar
wind reflection process could explain past ion observations at the Moon, and
the process should occur universally at all atmosphereless non-magnetized
objects.Comment: 12 pages, 8 figure
Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions
We have measured the current-voltage characteristics of small-capacitance
single Josephson junctions at low temperatures (T < 0.04 K), where the strength
of the coupling between the single junction and the electromagnetic environment
was controlled with one-dimensional arrays of dc SQUIDs. We have clearly
observed Coulomb blockade of Cooper-pair tunneling and even a region of
negative differential resistance, when the zero-bias resistance of the SQUID
arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative
differential resistance is evidence of coherent single-Cooper-pair tunneling in
the single Josephson junction.Comment: RevTeX, 4 pages with 6 embedded figure
Export of functional Streptomyces coelicolor alditol oxidase to the periplasm or cell surface of Escherichia coli and its application in whole-cell biocatalysis
Streptomyces coelicolor A3(2) alditol oxidase (AldO) is a soluble monomeric flavoprotein in which the flavin cofactor is covalently linked to the polypeptide chain. AldO displays high reactivity towards different polyols such as xylitol and sorbitol. These characteristics make AldO industrially relevant, but full biotechnological exploitation of this enzyme is at present restricted by laborious and costly purification steps. To eliminate the need for enzyme purification, this study describes a whole-cell AldO biocatalyst system. To this end, we have directed AldO to the periplasm or cell surface of Escherichia coli. For periplasmic export, AldO was fused to endogenous E. coli signal sequences known to direct their passenger proteins into the SecB, signal recognition particle (SRP), or Twin-arginine translocation (Tat) pathway. In addition, AldO was fused to an ice nucleation protein (INP)-based anchoring motif for surface display. The results show that Tat-exported AldO and INP-surface-displayed AldO are active. The Tat-based system was successfully employed in converting xylitol by whole cells, whereas the use of the INP-based system was most likely restricted by lipopolysaccharide LPS in wild-type cells. It is anticipated that these whole-cell systems will be a valuable tool for further biological and industrial exploitation of AldO and other cofactor-containing enzymes.
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