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511.
A high-pressure Fourier-transform infrared technique was used to probe the evolution of 2H bonds inside the helical segments of myoglobin in relation to p2H, Tris concentration in the medium and iron-ligand nature. The analysis was focused on changes in the conformation-sensitive amide-I' band, reflecting the peptide C = O group stretching vibrations coupled to the in-plane N-2H bending and C = N stretching modes. From data obtained under high pressure, the strength of 2H bonds, inside the alpha-helical segments of the protein at atmospheric pressure, is not simply a function of p2H and salt concentration. At low Tris concentration (50 mM), the strength of these 2H bonds increases with p2H, whereas for a higher Tris concentration (100 mM) this strength is lower at p2H 7 than at p2H 6.0 or 8.5. It is also observed that the azidometmyoglobin molecule exhibits tighter intrahelical interactions and lower sensitivity to pressure than aquametmyoglobin. Information is also presented regarding interhelical interactions in relation to the solvent. 相似文献
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Peter Alpert 《Oecologia》1999,120(1):69-76
In plants, only species with clonal growth are able to directly transfer resources between otherwise independent units of
the same genetic individual. A simple conceptual model of plant performance as a function of internal resource supply and
environmental resource availability suggests that resource sharing between ramets within clones is likely to be disadvantageous
in uniform habitats and advantageous in patchy ones. It was therefore hypothesized that clones in populations from relatively
uniform habitats will have been selected for low rates of resource sharing between ramets compared to clones in populations
from patchier habitats. In coastal northern California, the clonal herb Fragaria chiloensis is common both in grasslands, where resources are relatively uniform, and on sand dunes, where resources are more patchy.
It was predicted that clones from a grassland population of Fragaria would have “selfish” ramets with low rates of resource sharing compared to clones from an adjacent dune population. Ramets
were subjected to contrasting light levels with and without connection between ramets. Patterns of biomass accumulation were
consistent with the prediction. This appears to be the first report of genetically based variation in patterns of resource
sharing in clonal plants. It supports the idea that these patterns are locally selected to increase plant performance in habitats
with different patterns of resource availability.
Received: 19 August 1998 / Accepted: 4 March 1999 相似文献
514.
Amnon Licht Bertram E. Alpert Jacques J. Bourgoignie Detlef Schlondorff 《Prostaglandins & other lipid mediators》1981,22(1):1-10
The effect of acute infusion of the prostaglandin synthetase inhibitors — meclofenamate or indomethacin — was examined in awake rats. Studies were performed in normal rats undergoing either sodium or water diuresis and in salt-replete rats with chronic renal insufficiency. Prostaglandin synthetase inhibitors had no effect on renal plasma flow, glomerular filtration rate or fractional excretion of sodium in any of the groups. Absolute urinary excretion rates for sodium and potassium decreased only in the normal, salt-replete rats. In contrast, prostaglandin synthetase inhibitors consistently decreased urinary flow and osmolar clearance under all experimental conditions studied. In the normal, salt-replete rats the fall in urine flow was preceded by an increase in urinary excretion of cyclic AMP. These results show that inhibitors of prostaglandin synthesis enhance the ability of the kidney to reabsorb water. This effect may be secondary to increased cyclic AMP generation and to increased urea recirculation resulting in higher urea accumulation in the renal medulla. 相似文献
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