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991.
992.
The absorption of glycyl-l-leucine is studied using the small intestine of Rana pipiens perfused through the vascular bed. It is found that the transfer into the vascular bed of glycine and leucine from the peptide in the lumen occurs in part by a process independent from those for the transfer of the free amino acids. This process is particularly effective for the transfer of glycine. 相似文献
993.
P. A. Parsons 《Genetica》1993,89(1-3):245-253
1. Little evolutionary change may occur at species borders since the cost of accommodating environmental stresses is high.
Extreme examples of such stasis include cave animals in stable stressed environments and ‘living fossils’ in widely fluctuating
stressed environments.
2. Variability from the molecular to the organismic level tends to be high under extreme stress. At the developmental level,
the fitness of such variants may be low. This means that much developmental variability in natural populations may have little
evolutionary significance.
3. Rapid evolutionary change of morphological traits is most likely to be based upon genes acting late in a developmental
pathway under conditions which are ecologically and energetically permissive.
4. Although some increases in resistance to temperature extremes have been recorded in laboratory selection experiments, major
extensions of extremes in natural populations appear difficult to achieve. The energetic costs of surviving extremes at species
borders implies that the evolution of major developmental and morphological shifts is more likely to be a feature of populations
of more equable habitats. 相似文献
994.
995.
996.
997.
Francis H. Parsons 《BMJ (Clinical research ed.)》1899,2(2033):1706-1707
998.
Red blood cells, a source of factors which induce Neisseria gonorrhoeae to resistance to complement-mediated killing by human serum 总被引:5,自引:0,他引:5
P V Patel P M Martin M Goldner N J Parsons H Smith 《Journal of general microbiology》1984,130(11):2767-2770
Lysates of guinea pig or human red blood cells (RBC) contain far more of the factors that induce resistance in gonococci to complement-mediated killing by fresh human serum that do plasma or serum. As was previously found with serum, most of the resistance-inducing activity of guinea pig RBC lysates was found in ultrafiltrates with molecular weights of less than 5000. In contrast, and as with human serum, most of the resistance-inducing activity of human RBC lysates did not pass ultrafilters which removed molecules of less than 5000 daltons, although some active material of low molecular weight was present. 相似文献
999.
1000.