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排序方式: 共有439条查询结果,搜索用时 15 毫秒
1.
Ildikó Vidra Kálmán Simon László Institóris Ingeborg Csöregh Mátyás Czugler 《Carbohydrate research》1982,111(1):41-57
After hydrolysis of 1,6-dibromo-1,6-dideoxygalactitol (1) and 1,2:5,6-dianhydrogalactitol (2), 11 compounds were isolated, three of them as tritylated derivatives. Their structures were established on the basis of chemical evidence and, for four compounds, by X-ray diffraction. The main product of the hydrolysis of 1 was 3,6-anhydro-1-bromo-1-deoxy-dl-galactitol; the end-products of the hydrolysis of 2 were 1,5-anhydro-dl-galactitol, 2,5-anhydro-dl-altritol, and galactitol. 相似文献
2.
Polytene salivary gland nuclei of Chironomus pallidivittatus were transplanted into oocytes of Xenopus laevis which were then cultured in vitro for 18 h. The giant chromosomes and nucleoli as well as the entire nuclei enlarged considerably
in volume during this time. The polyteny and specific chromomere pattern of the chromosomes were maintained, and the puffing
of the salivary gland-specific Balbiani rings was not noticeably changed. — Polytene nuclei from differentiated insect cells
transplanted into Xenopus oocytes thus appear suited for exposing giant chromosomes in vivo to purified factors such as regulatory molecules.
This paper is dedicated to Professor Wolfgang Beermann on the occasion of his 60th birthday 相似文献
3.
Phosphate-Activated Glutaminase in the Crude Mitochondrial Fraction (P2 Fraction) from Human Brain Cortex 总被引:1,自引:1,他引:0
Gerd Svenneby Bjørg Roberg Svein Hogstad Ingeborg Aa. Torgner Elling Kvamme 《Journal of neurochemistry》1986,47(5):1351-1355
The kinetics and other properties of phosphate-activated glutaminase have for the first time been studied in the crude mitochondrial fraction (P2 fraction) from human brain. The enzyme is for unexplained reasons inactivated postmortem. The enzyme activity decreases by storing the tissue or homogenate at 37 degrees C. The inactivation is not caused by formation of a dialysable inhibiting compound. No large proteolytic degradation has occurred, since the phosphate-activated glutaminase-like immunoreactive band did not disappear during the storage. The molecular weight of the subunit of the enzyme as determined by immunoblots of sodium dodecyl sulfate-treated homogenates from human brain is estimated to be approximately 64 K. The enzyme has been shown to have a pH optimum of 8.6; it is activated by phosphate, inhibited by glutamate, and partially inhibited by ammonia. Double-inverse plots of enzyme activity against phosphate are concave-upward, and more so in the presence of an inhibitor. The inhibition by glutamate appears to be noncompetitive with the substrate glutamine, and competitive with the activator phosphate. These kinetic properties are not significantly different from our earlier observations concerning phosphate-activated glutaminase from pig brain and pig kidney. 相似文献
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Commonly used semiparametric estimators of causal effects specify parametric models for the propensity score (PS) and the conditional outcome. An example is an augmented inverse probability weighting (IPW) estimator, frequently referred to as a doubly robust estimator, because it is consistent if at least one of the two models is correctly specified. However, in many observational studies, the role of the parametric models is often not to provide a representation of the data-generating process but rather to facilitate the adjustment for confounding, making the assumption of at least one true model unlikely to hold. In this paper, we propose a crude analytical approach to study the large-sample bias of estimators when the models are assumed to be approximations of the data-generating process, namely, when all models are misspecified. We apply our approach to three prototypical estimators of the average causal effect, two IPW estimators, using a misspecified PS model, and an augmented IPW (AIPW) estimator, using misspecified models for the outcome regression (OR) and the PS. For the two IPW estimators, we show that normalization, in addition to having a smaller variance, also offers some protection against bias due to model misspecification. To analyze the question of when the use of two misspecified models is better than one we derive necessary and sufficient conditions for when the AIPW estimator has a smaller bias than a simple IPW estimator and when it has a smaller bias than an IPW estimator with normalized weights. If the misspecification of the outcome model is moderate, the comparisons of the biases of the IPW and AIPW estimators show that the AIPW estimator has a smaller bias than the IPW estimators. However, all biases include a scaling with the PS-model error and we suggest caution in modeling the PS whenever such a model is involved. For numerical and finite sample illustrations, we include three simulation studies and corresponding approximations of the large-sample biases. In a dataset from the National Health and Nutrition Examination Survey, we estimate the effect of smoking on blood lead levels. 相似文献
8.
Peter Miethe Ingeborg Jansen Uwe Niedermeyer Udo Kragl Regine Haftendorn Maria-Regina Kula Christian Wandrey Karl-Heinz Mohr Helmut-Walter Meyer 《Biocatalysis and Biotransformation》1992,7(1):61-73
The possibility of using the enzyme (R)-Oxynitrilase in a biphasic lyotropic liquid crystal/dibutylether system has been demonstrated. This reaction system is applicable for the continuous production of (R)-benzaldehydecyanohydrin in a fixed bed reactor. The optical purity was between 94 and 96% ee and independent of the flow rate. The space time yield was maximal (2650 g/(1*d)) at a flow rate of 1.6 ml/min. 相似文献
9.
Mariagrazia Grilli A. Gilbert Wright Jr. Ingeborg Hanbauer 《Journal of neurochemistry》1991,56(6):2108-2115
[3H]Dopamine uptake and [3H]cocaine binding sites were studied in primary cultures of ventral mesencephalon from 14-day-old rat embryos. Specific binding sites for [3H]cocaine and [3H]mazindol were detected only in intact cell cultures of ventral mesencephalon, and were absent in sonicated, washed membranes prepared from these cell cultures. [3H]Cocaine was not taken up by the cells through an active transport process because [3H]cocaine binding occurred also at 4 degrees C. Moreover, the possibility of [3H]cocaine entering the cells by passive diffusion and ion trapping was also excluded because extensive washing failed to remove [3H]cocaine from the cells. [3H]Cocaine binding was reduced to 6% of control when cells were permeabilized with streptolysin O (0.2 U/ml, 5 min). Taken together, these results suggest that in cultured mesencephalic neurons, [3H]cocaine may enter the cell by passive diffusion and then be sequestered by a cytosolic compartment that is lost in the process of permeabilization or sonication and washing of membrane preparations. Permeabilization of cultured neurons failed to alter the storage of [3H]dopamine. When cells were permeabilized with streptolysin O (0.2 U/ml; 5 min) after [3H]dopamine was taken up, [3H]dopamine was retained by the cells and did not leak into the incubation medium, indicating that [3H]dopamine was stored in sites that could not pass through the perforated membranes. In contrast, [3H]dopamine uptake into already permeabilized cells was reduced by 33%, suggesting that a cytosolic protein that had leaked out may play a functional role in the uptake process. In contrast to striatal membrane preparations of adult rats, [3H]cocaine binding in intact mesencephalic cell cultures was Na+ independent.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
10.
Gabriel von Euler Ingeborg van der Ploeg Bertil B. Fredholm Kjell Fuxe 《Journal of neurochemistry》1991,56(1):178-183
To examine whether GTP-binding proteins (G proteins) mediate the ability of neurotensin to lower the affinity of dopamine D2 agonist binding, the modulation by neurotensin in vitro of N-[3H]propylnorapomorphine [( 3H]-NPA) binding was investigated following pretreatment with pertussis toxin and N-ethylmaleimide in rat neostriatal membranes. Preincubation with N-ethylmaleimide (100 microM) markedly inhibited pertussis toxin-induced back-ADP ribosylation of three proteins with apparent molecular masses of 41, 40, and 39 kDa, respectively. This inhibition was prevented by adding dithiothreitol (250 microM) during the preincubation. N-Ethylmaleimide increased the KD (180 +/- 30%) and decreased the Bmax (-31 +/- 9%) of [3H]NPA binding sites but did not affect the binding properties of the selective D2 antagonist [3H]raclopride. N-Ethylmaleimide pretreatment did not affect the neurotensin (3 nM)-induced increase in the KD of [3H]NPA binding sites. Pertussin toxin treatment in vivo and in vitro was similarly ineffective. In conclusion, the present study indicates that neurotensin modulation of D2 agonist binding in neostriatal membranes is not mediated by G proteins. 相似文献