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31.
Background
Previously it has been shown that insulin-mediated tyrosine phosphorylation of myosin heavy chain is concomitant with enhanced association of C-terminal SRC kinase during skeletal muscle differentiation. We sought to identify putative site(s) for this phosphorylation event. 相似文献32.
ARBUCKLE RK 《California medicine》1954,80(5):360-362
Examination of the esophagus must go considerably beyond observation of "a barium swallow"; it must include a thorough study of the hypopharynx, the cervical esophagus and the thoracic esophagus. Dysphagia, which is almost always the presenting complaint, may be due to a number of lesions originating outside the esophagus and thus cause no sign of mucous membrane destruction or of filling defect. 相似文献
33.
Catchment land-use, macroinvertebrates and detritus processing in headwater streams: taxonomic richness versus function 总被引:3,自引:0,他引:3
ALEXANDER D. HURYN VIVIAN M. BUTZ HURYN CHRIS J. ARBUCKLE & LEONIDAS TSOMIDES 《Freshwater Biology》2002,47(3):401-415
1. We used a litter bag technique to assess the effect of catchment land-use (forest, wetland, agriculture, urban) on the processing of red maple ( Acer rubrum L.) litter in 17 streams in Maine, U.S.A. Litter processing by fungi was predicted to increase with nutrient concentrations along a gradient of land use, from relatively unmodified to highly modified. Litter processing by litter-shredding macroinvertebrates was predicted to decline along this gradient because of a decline in their taxonomic richness and biomass.
2. Land use was associated with the anticipated gradient in nutrient and macroinvertebrate attributes, and a significant relationship was found between land use and nitrate concentration. There was, however, no significant relationship between land use and soluble reactive phosphorus (SRP) concentration. Similarly, shredder taxonomic richness was significantly related to land use type, whereas shredder biomass showed no significant relationship to land use.
3. Attributes of the shredder assemblage structure and nutrient concentrations were both strong determinants of litter processing. Increasing biomass and taxonomic richness of shredders was significantly related to increasing rates of litter mass loss. Increasing concentrations of nitrate and SRP were significantly related to increasing rates of litter softening below threshold concentrations (approximately 0.20 mg NO3 -N L–1 and 5 μg SRP L–1 ).
4. The potentially additive effects of nitrate and SRP concentrations or shredder richness and biomass on litter processing rates were confounded by the lack of significant correlation between these pairs of variables. Consequently, rates of litter processing (as rates of softening or mass loss) did not vary systematically among different land use regimes. 相似文献
2. Land use was associated with the anticipated gradient in nutrient and macroinvertebrate attributes, and a significant relationship was found between land use and nitrate concentration. There was, however, no significant relationship between land use and soluble reactive phosphorus (SRP) concentration. Similarly, shredder taxonomic richness was significantly related to land use type, whereas shredder biomass showed no significant relationship to land use.
3. Attributes of the shredder assemblage structure and nutrient concentrations were both strong determinants of litter processing. Increasing biomass and taxonomic richness of shredders was significantly related to increasing rates of litter mass loss. Increasing concentrations of nitrate and SRP were significantly related to increasing rates of litter softening below threshold concentrations (approximately 0.20 mg NO
4. The potentially additive effects of nitrate and SRP concentrations or shredder richness and biomass on litter processing rates were confounded by the lack of significant correlation between these pairs of variables. Consequently, rates of litter processing (as rates of softening or mass loss) did not vary systematically among different land use regimes. 相似文献
34.
35.
WILLIAM J. ETGES KAREN L. ARBUCKLE MAX LEVITAN 《Biological journal of the Linnean Society. Linnean Society of London》2006,88(1):131-141
We resurveyed an elevational transect in the Great Smoky Mountains National Park first sampled in 1947 for chromosomal polymorphisms in populations of Drosophila robusta . Combining these results with those from previous surveys, unpublished data, and long-term meteorological data from this region up to 2003, we found that these chromosomal polymorphisms had continued to shift in frequency consistent with long-term temperature changes, yet had maintained elevational clines. Intensity of linkage disequilibrium for X-chromosome gene arrangements had shifted up and down the transect over the 56-year sampling period, suggesting shifting patterns of adaptation. Chromosomal frequency changes through the 1980s clearly demonstrated concerted directional evolution in response to cooler temperatures, but over the 20 years until 2003, frequency changes in most high-elevation populations reversed for many of the most temperature-sensitive gene arrangements. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 131–141. 相似文献
36.
O. ÜNAL R. SÜLEYMAN GÖKTÜRK 《Botanical journal of the Linnean Society. Linnean Society of London》2003,142(4):465-468
A new species Scorzonera gokcheoglui O. Ünal & R. S. Göktürk sp. nov. from south Anatolia is described and illustrated. Its relationships with S. argyria and S. pisidica are discussed. A map showing the distribution of the species and other related species is given. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 465–468. 相似文献
37.
Previously it has been shown that insulin-mediated tyrosine phosphorylation of myosin heavy chain is concomitant with enhanced association of C-terminal SRC kinase during skeletal muscle differentiation. We sought to identify putative site(s) for this phosphorylation event. A combined bioinformatics approach of motif prediction and evolutionary and structural analyses identified tyrosines163 and 1856 of the skeletal muscle heavy chain as the leading candidate for the sites of insulin-mediated tyrosine phosphorylation. Our work is suggestive that tyrosine phosphorylation of myosin heavy chain, whether in skeletal muscle or in platelets, is a significant event that may initiate cytoskeletal reorganization of muscle cells and platelets. Our studies provide a good starting point for further functional analysis of MHC phosphor-signalling events within different cells. 相似文献
38.
Two groups control light-induced schiff base deprotonation and the proton affinity of asp(85) in the Arg(82)His mutant of bacteriorhodopsin 总被引:1,自引:0,他引:1
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ES Imasheva SP Balashov TG Ebrey N Chen RK Crouch DR Menick 《Biophysical journal》1999,77(5):2750-2763
Arg(82) is one of the four buried charged residues in the retinal binding pocket of bacteriorhodopsin (bR). Previous studies show that Arg(82) controls the pK(a)s of Asp(85) and the proton release group and is essential for fast light-induced proton release. To further investigate the role of Arg(82) in light-induced proton pumping, we replaced Arg(82) with histidine and studied the resulting pigment and its photochemical properties. The main pK(a) of the purple-to-blue transition (pK(a) of Asp(85)) is unusually low in R82H: 1.0 versus 2.6 in wild type (WT). At pH 3, the pigment is purple and shows light and dark adaptation, but almost no light-induced Schiff base deprotonation (formation of the M intermediate) is observed. As the pH is increased from 3 to 7 the M yield increases with pK(a) 4.5 to a value approximately 40% of that in the WT. A transition with a similar pK(a) is observed in the pH dependence of the rate constant of dark adaptation, k(da). These data can be explained, assuming that some group deprotonates with pK(a) 4.5, causing an increase in the pK(a) of Asp(85) and thus affecting k(da) and the yield of M. As the pH is increased from 7 to 10.5 there is a further 2.5-fold increase in the yield of M and a decrease in its rise time from 200 &mgr;s to 75 &mgr;s with pK(a) 9. 4. The chromophore absorption band undergoes a 4-nm red shift with a similar pK(a). We assume that at high pH, the proton release group deprotonates in the unphotolyzed pigment, causing a transformation of the pigment into a red-shifted "alkaline" form which has a faster rate of light-induced Schiff base deprotonation. The pH dependence of proton release shows that coupling between Asp(85) and the proton release group is weakened in R82H. The pK(a) of the proton release group in M is 7.2 (versus 5.8 in the WT). At pH < 7, most of the proton release occurs during O --> bR transition with tau approximately 45 ms. This transition is slowed in R82H, indicating that Arg(82) is important for the proton transfer from Asp(85) to the proton release group. A model describing the interaction of Asp(85) with two ionizable residues is proposed to describe the pH dependence of light-induced Schiff base deprotonation and proton release. 相似文献
39.
Structural analysis of human neutrophil migration: Centriole, microtubule, and microfilament orientation and function during chemotaxis 总被引:41,自引:21,他引:20
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Orientation of nucleus, centriole, microtubules, and microfilaments within human neutrophils in a gradient of chemoattractant (5 percent Escherichia coli endotoxin-activated serum) was evaluated by electron microscopy. Purified neutropils (hypaque-Ficoll) were placed in the upper compartment of chemotactic chambers. Use of small pore (0.45 μm) micropore filters permitted pseudopod penetration, but impeded migration. Under conditions of chemotaxis with activated serum beneath the filter, the neutrophil population oriented at the filter surface with nuclei located away from the stimulus, centrioles and associated radial array of microtubules beneath the nuclei, and microfilament-rich pseudopods penetrating the filter pores. Reversal of the direction of the gradient of the stimulus (activated serum above cells) resulted in a reorientation of internal structure which preceded pseudopod formation toward the activated serum and migration off the filter. Coordinated orientation of the entire neutrophil population did not occur in buffer (random migration) or in a uniform concentration of activated serum (activated random migration). Conditions of activated random migration resulted in increased numbers of cells with locomotory morphology, i.e. cellular asymmetry with linear alignment of nucleus, centriole, microtubule array, and pseudopods. Thus, activated serum increased the number of neutrophils exhibiting locomotory morphology, and a gradient of activated serum induced the alignment of neutrophils such that this locomotory morphology was uniform in the observed neutrophil populayion. In related studies, cytochalasin B and colchicines were used to explore the role of microfilaments and microtubules in the neutrophil orientation and migration response to activated serum. Cytochalasin B (3.0 μg/ml) prevented migration and decreased the microfilaments seen, but allowed normal orientation of neutrophil structures. In an activated serum gradient, colchicines, but not lumicolchicine, decreased the orientation of nuclei and centrioles, and caused a decrease in centriole-associated microtubules in concentrations as low as 10(-8) to 10(-7) M. These colchicines effects were associated with the rounding of cells and impairment of pseudopod formation. The impaired pseudopod formation was characterized by an inability to form pseudopods in the absence of a solid substrate, a formation of narrow pseudopods within a substrate, and a defect in pseudopod orientation in an activated serum gradient. Functional studies of migration showed that colchicines, but not lumicolchicine, minimally decreased activated random migration and markedly inhibited directed migration, but had not effect on random migration. These studies show that, although functioning microfilaments are probably necessary for neutrophil migration, intact microtubules are essential for normal pseudopod formation and orientation, and maximal unidirectional migration during chemotaxis. 相似文献
40.
Worldwide patterns of mitochondrial DNA differentiation in the harbor seal (Phoca vitulina) 总被引:3,自引:0,他引:3
Stanley HF; Casey S; Carnahan JM; Goodman S; Harwood J; Wayne RK 《Molecular biology and evolution》1996,13(2):368-382
The harbor seal (Phoca vitulina) has one of the broadest geographic
distributions of any pinniped, stretching from the east Baltic, west across
the Atlantic and Pacific Oceans to southern Japan. Although individuals may
travel several hundred kilometers on annual feeding migrations, harbor
seals are generally believed to be philopatric, returning to the same areas
each year to breed. Consequently, seals from different areas are likely to
be genetically differentiated, with levels of genetic divergence increasing
with distance. Differentiation may also be caused by long-standing
topographic barriers such as the polar sea ice. We analyzed samples of 227
harbor seals from 24 localities and defined 34 genotypes based on 435 bp of
control region sequence. Phylogenetic analysis and analysis of molecular
variance showed that populations in the Atlantic and Pacific Oceans and
east and west coast populations of these oceans are significantly
differentiated. Within these four regions, populations that are
geographically farthest apart generally are the most differentiated and
often do not share genotypes or differ in genotype frequency. The average
corrected sequence divergence between populations in the Atlantic and
Pacific Oceans is 3.28% +/- 0.38% and those among populations within each
of these oceans are 0.75% +/- 0.69% and 1.19% +/- 0.65%, respectively. Our
results suggest that harbor seals are regionally philopatric, on the scale
of several hundred kilometers. However, genetic discontinuities may exist,
even between neighboring populations such as those on the Scottish and east
English coasts or the east and west Baltic. The mitochondrial data are
consistent with an ancient isolation of populations in both oceans, due to
the development of polar sea ice. In the Atlantic and Pacific, populations
appear to have been colonized from west to east with the European
populations showing the most recent common ancestry. We suggest the recent
ancestry of European seal populations may reflect recolonization from Ice
Age refugia after the last glaciation.
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