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Siham Bouahim Laïla Rhazi Btissam Amami Nargis Sahib Mouhssine Rhazi Aline Waterkeyn Abdelmjid Zouahri François Mesleard Serge D. Muller Patrick Grillas 《Comptes rendus biologies》2010,333(9):670-679
The impact of grazing on the vegetation of Moroccan temporary pools has been studied at 2 scales: regional (inter-pools) and local (intra-pools). Half of the 16 forest pools studied is located in a reserve and ungrazed. The other half, located within public forest, is grazed. Vegetation relevés coupled to water-depths measurements were carried out in each pool. The results showed a significant effect of grazing on both scales of analysis. This effect was found in the species composition of the vegetation, which differed between the 2 types of pools, and in the lower species richness and abundance of plant species in the grazed pools. These differences are interpreted as resulting from the selection by herbivores and the differential tolerance of species to disturbance. These impacts are likely to expose certain species to local extinction by reducing their populations. 相似文献
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The aspartate and alanine aminotransferases in the tissues of the snail, Pila globosa showed high catalytic potentials (low Km and high Vmax) during malathion exposure in vivo. In vitro addition of different concentrations of malathion did not influence aminotransferase activity. The results are discussed in relation to the regulative influence of the intracellular environment of the cell. 相似文献
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Kabeer I. Ahammad Sahib Durisala Desaiah 《Journal of biochemical and molecular toxicology》1986,1(4):55-66
Previous studies from this laboratory have indicated that tricyclohexyltin hydroxide (Plictran) is a potent inhibitor of both basal- and isoproterenol-stimulated cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase, with an estimated IC-50 of 2.5 × 10?8M. The present studies were initiated to evaluate the mechanism of inhibition of Ca2+-ATPase by Plictran. Data on substrate and cationic activation kinetics of Ca2+-ATPase indicated alteration of Vmax and Km by Plictran (1 and 5×10?8M), suggesting a mixed type of inhibition. The beta-adrenergic agonist isoproterenol increased Vmax of both ATP- and Ca2+-dependent enzyme activities. However, the Km of enzyme was decreased only for Ca2+ Plictran inhibited isoproterenol-stimulated Ca2+-ATPase activity by altering both and Vmax and Km of ATP as well as Ca2+-dependent enzyme activities, suggesting that after binding to a single independent site, Plictran inhibits enzyme catalysis by decreasing the affinity of enzyme for ATP as well as for Ca2+ Preincubation of enzyme with 15 μM cAMP or the addition of 2mM ATP to the reaction mixture resulted in slight activation of Plictran-inhibited enzyme. Pretreatment of SR with 5 × 10?7M propranolol and 5 × 10?8M Plictran resulted in inhibition of basal activity in addition to the loss of stimulated activity. Preincubation of heart SR preparation with 5 × 10?5M coenzyme A in combination with 5 × 10?8M Plictran partly restored the beta-adrenergic stimulation. These results suggest that some critical sites common to both basal- and beta-adrenergic-stimulated Ca2+-ATPase are sensitive to binding by Plictran, and the resultant conformational change may lead to inhibition of beta-adrenergic stimulation. 相似文献
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Identification and origin of oestradiol-binding protein in immature rat skin. Demonstration of oestrophilic alpha-foetoprotein synthesis and secretion by developing rat skin explants in culture. 总被引:1,自引:1,他引:0
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Oestrophilic alpha-foetoprotein (alpha FP) is found in high concentrations in developing rat skin cytosol. Elevated levels of alpha FP observed in foetal-rat skin decreased during development, and the protein became undetectable after 3 weeks of postnatal life. The developmental profile of alpha FP in skin is different from that in foetal blood. alpha FP in skin arises as a result of its synthesis in situ in the epidermal cells. Synthesis of alpha FP in skin is demonstrated by linear incorporation of [14C]leucine into immunoprecipitable, intracellular alpha FP by skin explants during 6 h in culture. Secretion is demonstrated by incorporation into alpha FP in culture medium. The rate of alpha FP synthesis in skin also declined with age and its synthesis is completely switched off 2 weeks after birth. The skin alpha FP level during development is regulated by controlling the rate of its synthesis in skin. alpha FP synthesized and secreted by skin is immunologically, electrophoretically and, with respect to molecular weight and oestradiol-binding properties, similar to that found in foetal serum. alpha FP was also identified as the major oestradiol-binding protein present in newborn-rat skin or secreted by newborn-rat skin explants in culture. 相似文献
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Interaction of [125I]-insulin with intact hepatocytes and its correlation with circulatory insulin level was examined. The hepatocytes from new-born rats bound lowest amount of [125I]-insulin (1.39±0.41 pM/mg cell protein) when circulatory insulin level was high (8±1.5 ΜU/ml). Hepatocytes from 7 day and 21 day old animals demonstrated a more or less similar relationship, Cells from 31 day old animals exhibited maximum insulin binding, activity (5.13±0.18.pM/mg cell protein) against a low serum insulin level (4.25±0.25 ΜU/ ml). Scatchard analysis of insulin binding shows that the affinity is higher in the hepatocytes from new-born animals than in the hepatocytes of 31 day old animals. Higher binding observed in the latter case may be due to a greater number of binding sites. Hepatocytes from one year old rats bound very little insulin (2.50±0.36 pM/mg cell protein) against a high circulatory insulin level (9.25±0.85 ΜU/ml). In view of these results, it appears that the down-regulation hypothesis holds true during ontogeny too. 相似文献
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The sublethal toxic potency of malathion in inhibiting acetylcholinesterase activity of brain, muscle, gill and liver tissues
of the fish,Tilapia mossambica was studied at 12 h intervals. Maximum in hibition at 36 and 48 h, and complete revival of acetylcholinesterase activity
after 72 h was noticed, suggestive of the loss of inhibition of the enzyme activity was probably by suitable (acetylcholine)
accumulation. 相似文献
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