2,464 research outputs found
Alternate routes to the cell surface underpin insulin-regulated membrane trafficking of GLUT4
Insulin-stimulated delivery of glucose transporters (GLUT4) from specialized intracellular GLUT4 storage vesicles (GSVs) to the surface of fat and muscle cells is central to whole-body glucose. This translocation and subsequent internalization of GLUT4 back into intracellular stores transits numerous small membrane-bound compartments (internal GLUT4-containing vesicles; IGVs) including GSVs, but the function of these different compartments is not clear. Cellugyrin and sortilin define distinct populations of IGV; sortilin-positive IGVs represent GSVs, but the function of cellugyrin-containing IGVs is unknown. Here we demonstrate a role for cellugyrin in intracellular sequestration of GLUT4 in HeLa cells and have used a proximity ligation assay to follow changes in pairwise associations between cellugyrin, sortilin, GLUT4 and membrane trafficking machinery following insulin-stimulation of 3T3-L1 adipoctyes. Our data suggest that insulin stimulates traffic from cellugyrin- to sortilin- membranes, and that cellugyrin-IGVs provide an insulin-sensitive reservoir to replenish GSVs following insulin-stimulated exocytosis of GLUT4. Furthermore, our data support the existence of a pathway from cellugyrin-membranes to the surface of 3T3-L1 adipocytes that bypasses GSVs under basal conditions, and that insulin diverts traffic away from this into GSVs
A comparison of feeding reconstituted and dried milk upon the growth and carcass composition of calves
1. The live-weight gain, carcass weight, edible carcass composition, efficiency of food conversion, and roughage intake were measured in three groups of calves fed for 87 d. After a 3-week feeding period on a common regimen, one group of calves was weaned on to a diet of dry whole-milk powder and chopped lucerne, the second group received a similar diet except that the whole-milk powder was reconstituted to a liquid milk, containing 12â15% dry matter. The third group was given the diet in the same manner as the second group except that the chopped lucerne was available ad lib. 2. The mean live-weight gains for the three groups were 37.7, 47.6 and 52.7 kg respectively, the differences between the dry-fed and the liquid-fed groups being highly significant. 3. Energy and nitrogen accretion in the edible carcass and efficiency of food conversion were superior in the second and third groups. 4. The third group ate larger quantities of roughage, though the difference did not reach significance. 5. The reasons for the superiority of the liquid milk diet are discussed in relation to the avoidance of ruminal fermentation of the milk
Comparison of two methods for describing the strain profiles in quantum dots
The electronic structure of interfaces between lattice-mismatched
semiconductor is sensitive to the strain. We compare two approaches for
calculating such inhomogeneous strain -- continuum elasticity (CE, treated as a
finite difference problem) and atomistic elasticity (AE). While for small
strain the two methods must agree, for the large strains that exist between
lattice-mismatched III-V semiconductors (e.g. 7% for InAs/GaAs outside the
linearity regime of CE) there are discrepancies. We compare the strain profile
obtained by both approaches (including the approximation of the correct C_2
symmetry by the C_4 symmetry in the CE method), when applied to C_2-symmetric
InAs pyramidal dots capped by GaAs.Comment: To appear in J. Appl. Physic
MoleculeâInduced Radical Formation (MIRF) ReactionsâA Reappraisal
Radical chain reactions are commonly initiated through the thermal or photochemical activation of purposeâbuilt initiators, through photochemical activation of substrates, or through wellâdesigned redox processes. Where radicals come from in the absence of these initiation strategies is much less obvious and are often assumed to derive from unknown impurities. In this situation, moleculeâinduced radical formation (MIRF) reactions should be considered as wellâdefined alternative initiation modes. In the most general definition of MIRF reactions, two closedâshell molecules react to give a radical pair or biradical. The exact nature of this transformation depends on the Ïâ or Ïâbonds involved in the MIRF process, and this Minireview specifically focuses on reactions that transform two Ïâbonds into two radicals and a closedâshell product molecule
Structure of the Draco Dwarf Spheroidal Galaxy
This article studies the structure of the Draco dwarf spheroidal galaxy with
an emphasis on the question of whether the spatial distribution of its stars
has been affected by the tidal interaction with the Milky Way, using R- and
V-band CCD photometry for eleven fields. The article reports coordinates for
the center, a position angle of the major axis, and the ellipticity. It also
reports the results of searches for asymmetries in the structure of Draco.
These results, and searches for a ``break'' in the radial profile and for the
presence of principal sequences of Draco in a color-magnitude diagram for
regions more than 50 arcmin from the center, yield no evidence that tidal
forces from the Milky Way have affected the structure of Draco.Comment: 25 pages, 11 figures, 3 tables. Accepted for publication in A
Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots
We report significant deviations from the usual quadratic dependence of the
ground state interband transition energy on applied electric fields in
InAs/GaAs self-assembled quantum dots. In particular, we show that conventional
second-order perturbation theory fails to correctly describe the Stark shift
for electric field below kV/cm in high dots. Eight-band calculations demonstrate this effect is predominantly due to
the three-dimensional strain field distribution which for various dot shapes
and stoichiometric compositions drastically affects the hole ground state. Our
conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure
Anomalous quantum confined Stark effects in stacked InAs/GaAs self-assembled quantum dots
Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs)
are predicted to exhibit a strong non-parabolic dependence of the interband
transition energy on the electric field, which is not encountered in single SAD
structures nor in other types of quantum structures. Our study based on an
eight-band strain-dependent Hamiltonian indicates that
this anomalous quantum confined Stark effect is caused by the three-dimensional
strain field distribution which influences drastically the hole states in the
stacked SAD structures.Comment: 4 pages, 4 figure
Diversity, genetic structure and evidence of outcrossing in British populations of the rock fern Adiantum capillus-veneris using microsatellites
Microsatellites were isolated and a marker system was developed in the fern Adiantum capillus-veneris. Polymorphic markers were then used to study the genetic diversity and structure of populations within the UK and Ireland where this species grows at the northern edge of its range, requiring a specific rock habitat and limited to a few scattered populations. Three dinucleotide loci detected a high level of diversity (23 alleles and 28 multilocus genotypes) across the UK and Ireland, with nearly all variation partitioned among rather than within populations. Of 17 populations represented by multiple samples, all except four were monomorphic. Heterozygosity was detected in three populations, all within Glamorgan, Wales (UK), showing evidence of outcrossing. We make inferences on the factors determining the observed levels and patterns of genetic variation and the possible evolutionary history of the populations
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