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133.
C. Köckert S. Abens U. Escher B. Kluge A. Gladun S. Sahling M. Schneider 《Journal of Low Temperature Physics》2001,124(3-4):477-495
Glasslike anomalies of low-temperature thermal properties were observed for the polycrystalline Nb37Ti63 alloy and Nb37Ti63 doped with deuterium. A giant heat release effect was found in (Nb-Ti)92D8 corresponding to a spectral density of two level systems of 7.8·1045 J–1 m–3. After rapid cooling of the sample a length relaxation with a quadratic dependence on the starting temperature was detected obeying a logarithmic time dependence. The results fit to the standard tunneling model assuming a temperature and time independent Grüneisen parameter. A constant Grüneisen parameter is compatible with a constant deformation potential but requires /V to depend on /0. For both systems the thermal expansion coefficient exhibits a linear temperature term in the superconducting state dominating below 1 K. 相似文献
134.
The purpose of this study was to compare the efficiency of two different Gq protein-coupled receptors (AT1 receptor for angiotensin II and B2 receptor for bradykinin) to activate phospholipase C (PLC). When the receptors were expressed at a similar level of 0.5 pmol/mg of protein, inositol trisphosphate (IP) accumulation elicited by AT1 receptor was four times higher than that elicited by B2 receptor. Genistein and pertussis toxin did not modify AT1 receptor- or B2 receptor-induced IP accumulation. These results indicate that in COS-7 cells, the two receptors activate PLC beta through G proteins of the Gq family. AT1 or B2 receptors were co-expressed with the alpha subunit of either Gq or G11. Both alpha subunits potentiated to the same extent AT1 receptor-induced IP accumulation. alpha 11 was also as efficient as alpha q to potentiate B2 receptor-induced response. Interestingly, however, the potentiating effect of alpha q and alpha 11 was more important (by 5-fold) on AT1 receptor-mediated response than on B2 receptor-mediated response. These results demonstrate that the extent of activation of PLC beta by different Gq-coupled receptors depends on the level of expression of these receptors and on their coupling efficiency. These are important parameters that determine the relative contribution of specific hormones to different biological processes. 相似文献
135.
Kretschmann A Ashauer R Preuss TG Spaak P Escher BI Hollender J 《Environmental science & technology》2011,45(11):4995-5002
A toxicokinetic model for Daphnia magna , which simulates the internal concentration of the insecticide diazinon, its detoxification product 2-isopropyl-6-methyl-4-pyrimidinol, and its active metabolite diazoxon, is presented. During in vivo exposure to diazinon with and without inhibition of cytochrome P450 by piperonyl butoxide, the parent compound as well as its metabolites were quantified with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) in extracts of D. magna . Rate constants of all relevant toxicokinetic steps were obtained by modeling the time course of the internal concentrations with a multicomponent first-order kinetics model. When cytochrome P450 was inhibited, the kinetic bioconcentration factor (BCF) of diazinon increased from 17.8 to 51.0 mL·g(ww)(-1). This clearly indicates that diazinon is biotransformed to a high degree by cytochrome P450 in D. magna . The dominant elimination step of diazinon was shown to be its oxidative dearylation to pyrimidinol (62% of total elimination) with a corresponding rate constant of 0.16 h(-1). In contrast, oxidative activation to diazoxon with a rate constant of 0.02 h(-1) amounted to only 8% of the total elimination. During exposure to diazinon, the active metabolite diazoxon could be detected only in very low concentrations (approximately 0.5% of the parent compound), presumably due to a very fast reaction with the target site acetylcholinesterase. During the exposure experiments (no feeding of daphnids), an exponential decline of the lipid content in D. magna with a first-order rate constant of 0.013 h(-1) was observed. For short exposure times (≤ 24 h), this had only a minor influence on the determined TK parameters. Such a TK model containing detailed biotransformation processes is an important tool for estimation of the toxic potential of chemicals, particularly, when active metabolites are formed inside an organism. 相似文献