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排序方式: 共有266条查询结果,搜索用时 15 毫秒
1.
Ana E. Lemus Felipe Vilchis Rebeca Damsky Bertha A. Ch vez Gustavo A. Garcí a Ivonne Grillasca Gregorio P rez-Palacios 《The Journal of steroid biochemistry and molecular biology》1992,41(3-8):881-890
Levonorgestrel (LNG) is a synthetic steroid that displays potent progestional and androgenic effects but it lacks estrogen-like activity. To examine the mode of action of this progestin, we studied its metabolism in vitro in target organs and the specific interactions of LNG and its metabolites with putative steroid receptors. The results demonstrated that [3H]LNG was efficiently converted to A-ring reduced derivatives when incubated with rat hypothalamus and pituitary. Under optimal incubation conditions, [3H]5-dihydro LNG (5-LNG) and [3H]3-5-tetrahydro LNG (3,5-LNG) were identified as the major metabolic conversion products, while [3H]3ß, 5-LNG formation occured to a lesser extent. A-ring reduction of LNG was NADPH-dependent. Assessment of the relative binding affinities of LNG and its derivatives to progesterone (PR), androgen (AR) and estrogen (ER) receptors by displacement analysis revealed that unchanged LNG binds with high affinity to PR and AR but not to ER. 5-LNG exhibited a diminished though significant interactions with PR and an enhanced binding affinity for AR as compared with LNG, indicating that 5-reduction of LNG increases its affinity for AR. The most striking finding was that further reduction of the 5-LNG molecule at C-3 abolished its binding activity to PR, AR, and even to ER. The overall data provides a plausible explanation for the lack of estrogen agonistic action of LNG and for its potent progestational and androgenic effects. 相似文献
2.
To examine the sensitivities of partially purified dopamine receptors to various dopaminergic agonists and antagonists, canine brain striatum dopamine receptors were enriched by isoelectric focusing. The digitonin-solubilized receptors were prelabelled with [3H]spiperone and focused for two time periods. After 5 h (incomplete focusing), radioactive peaks were detected at pH 6 and 9-11. Only the pH 6 peak revealed drug sensitivities expected of D2 receptors. Receptor recovery of the pH 6 peak was 79% with purification being sevenfold. After focusing overnight to equilibrium, the pH 6 peak further separated into peaks at pH 4.6 and 6.8. The receptor was identified only in the pH 4.6 fraction. The recovery of receptors in the pH 4.6 peak was low (10%), indicating little enrichment of the receptor. The rank order of binding of neuroleptics and dopamine agonists to the purified material was similar to that of the original preparation of soluble receptors. Dopamine did not bind to the purified pH 4.6 fraction unless the phosphate buffer (used during focusing) was replaced with Tris buffer. The absence of receptors in the pH 6.8 and pH 10 fractions, although both contained prelabeled [3H]spiperone, indicates the importance of testing agonists and antagonists on each fraction at each step in purification. 相似文献
3.
A Direct Screening Procedure for Gravitropism Mutants in Arabidopsis thaliana (L.) Heynh. 总被引:5,自引:5,他引:0
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Bertha L. Bullen Thérèse R. Best Mary M. Gregg Sara-Ellen Barsel Kenneth L. Poff 《Plant physiology》1990,93(2):525-531
In order to isolate gravitropism mutants of Arabidopsis thaliana (L.) Heynh. var Estland for the genetic dissection of the gravitropism pathway, a direct screening procedure has been developed in which mutants are selected on the basis of their gravitropic response. Variability in hypocotyl curvature was dependent on the germination time of each seed stock, resulting in the incorrect identification of several lines as gravitropism mutants when a standard protocol for the potentiation of germination was used. When the protocol was adjusted to allow for differences in germination time, these lines were eliminated from the collection. Out of the 60,000 M2 seedlings screened, 0.3 to 0.4% exhibited altered gravitropism. In approximately 40% of these mutant lines, only gravitropism by the root or the hypocotyl was altered, while the response of the other organ was unaffected. These data support the hypothesis that root and hypocotyl gravitropism are genetically separable. 相似文献
4.
Una S. Ryan Marlene Absher Bertha M. Olazabal Lynn M. Brown James W. Ryan 《Tissue & cell》1982,14(4):637-649
A fundamental characteristic of vascular endothelium is that it exists as a monolayer, a condition that must be met in both vascular growth and repair. Maintenance of the monolayer is important both for the exchange of nutrients and for interactions between blood solutes and endothelial enzymes and transport systems. We have used time-lapse cinematography to compare proliferative behavior of bovine pulmonary endothelial cells in (1) establisment of a monolayer from a low-density seed (7.5 × 104 cells in a 60 mm dish) and (2) restitution of a confluent monolayer (approx. 2.9 × 106 cells in a 60 mm dish) following a mechanical wound (removal of cells from an area 5 × 15 mm by scraping). Culture 2 was not refed after wounding. In culture 2, approx. 30% of the cells accounted for repopulation (confluence in 40 hr). In culture I, all cells entered into division. Participating cells of culture 2 began division immediately (69 divisions/filmed area in 10 hr, vs. four divisions in culture I). Interdivision times (IDT) were longer and relatively constant in culture I until near confluence; none were < 10 h, whereas in 2, 24% of the IDT's were ≤ 10 hr. Remarkably, IDTs of culture 2 decreased steadily until confluence was re-established. Cell migration in culture 1 was multidirectional while direction of migration in culture 2 was always into the wound area. Mean migration rate (MIG) in culture 2 was related to the site of origin of the cells, those dividing farthest from the unwounded area had fastest MIGs. Neither culture formed more than a single layer of cells. Although the cell kinetics of cultures 1 and 2 differed, the same goal, confluence, was achieved in either case. 相似文献
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6.
Lubomir Prochazka Stepan Koudelka Lan-Feng Dong Jan Stursa Jacob Goodwin Jiri Neca Josef Slavik Miroslav Ciganek Josef Masek Katarina Kluckova Maria Nguyen Jaroslav Turanek Jiri Neuzil 《Apoptosis : an international journal on programmed cell death》2013,18(3):286-299
α-Tocopheryl succinate (α-TOS) is a promising anti-cancer agent due to its selectivity for cancer cells. It is important to understand whether long-term exposure of tumour cells to the agent will render them resistant to the treatment. Exposure of the non-small cell lung carcinoma H1299 cells to escalating doses of α-TOS made them resistant to the agent due to the upregulation of the ABCA1 protein, which caused its efflux. Full susceptibility of the cells to α-TOS was restored by knocking down the ABCA1 protein. Similar resistance including ABCA1 gene upregulation was observed in the A549 lung cancer cells exposed to α-TOS. The resistance of the cells to α-TOS was overcome by its mitochondrially targeted analogue, MitoVES, that is taken up on the basis of the membrane potential, bypassing the enhanced expression of the ABCA1 protein. The in vitro results were replicated in mouse models of tumours derived from parental and resistant H1299 cells. We conclude that long-term exposure of cancer cells to α-TOS causes their resistance to the drug, which can be overcome by its mitochondrially targeted counterpart. This finding should be taken into consideration when planning clinical trials with vitamin E analogues. 相似文献
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8.
Abstract Oochoristica novaezealandae n. sp. is described from the small intestine of a skink, Leiolopisma nigriplantare maccanni (Hardy 1977) from Birdling's Flat, Banks Peninsula, South Island, New Zealand. In having fewer than 20 testes it differs from all other species in the genus except O. chinensis Jensen, Schmidt & Kuntz, 1983; O. vacuolata Hickman, 1954; O. lygosomae Burt, 1933; and O. lygosomatis Skinker, 1935. Of these, it most resembles O. chinensis, but differs from it in the ovary, which consists of 2 rounded lobes; they are subdivided into finger-like lobules in O. chinensis. Further, O. novaezealandae has a conspicuous, encapsulated, sac-like mass of glands surrounding the genital atrium; these are not present in O. chinensis. 相似文献
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10.
Phylogenetic relationships among Andean-Ecuadorian and other Neotropical populations of Anastrepha fraterculus and related species have been studied using two regions of mtDNA : 405 base pairs within Cytochrome Oxidase I ( COI) and 224 base pairs within Cytochrome Oxidase II (COII). Phylogenetic relationships were inferred using Maximun Parsimony (MP) method and haplotype networks. Andean-Ecuadorian populations of A. fraterculus are monomorphic at the COI locus and fall within a clade of South-American lowland populations of A. fraterculus. They appear to be unrelated with populations of northern Andes of Colombia and Venezuela also assigned to A. fraterculus, meaning that this species, as currently circumscribed, is not monophyletic and is composed of different biological entities that are little differentiated morphologically. At the COII locus, Andean-Ecuadorian populations of A. fraterculus show a major haplotype with a few variants, and form a clade with the lowland populations of southern Brazil an Argentina, but are clearly differentiated from them. Andean-Ecuadorian populations of Anastrepha fraterculus appear to be homogeneous with respect to their mitochondrial genome and thus their identity as members of a single gene pool is confirmed by these results. 相似文献