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排序方式: 共有250条查询结果,搜索用时 31 毫秒
241.
242.
Noncontact dipole effects on channel permeation. III. Anomalous proton conductance effects in gramicidin 总被引:3,自引:2,他引:1
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LR Phillips CD Cole RJ Hendershot M Cotten TA Cross DD Busath 《Biophysical journal》1999,77(5):2492-2501
Proton transport on water wires, of interest for many problems in membrane biology, is analyzed in side-chain analogs of gramicidin A channels. In symmetrical 0.1 N HCl solutions, fluorination of channel Trp(11), Trp-(13), or Trp(15) side chains is found to inhibit proton transport, and replacement of one or more Trps with Phe enhances proton transport, the opposite of the effects on K(+) transport in lecithin bilayers. The current-voltage relations are superlinear, indicating that some membrane field-dependent process is rate limiting. The interfacial dipole effects are usually assumed to affect the rate of cation translocation across the channel. For proton conductance, however, water reorientation after proton translocation is anticipated to be rate limiting. We propose that the findings reported here are most readily interpreted as the result of dipole-dipole interactions between channel waters and polar side chains or lipid headgroups. In particular, if reorientation of the water column begins with the water nearest the channel exit, this hypothesis explains the negative impact of fluorination and the positive impact of headgroup dipole on proton conductance. 相似文献
243.
Changes in levels of sex steroids and gonadotropins were measured in 16 normal prepubertal and 15 pubertal girls prior to and after a 3 hour infusion of 100 microgrm synthetic gonadotropin releasing hormone (Gn-RH). Plasa estradiol (E2) concentrations rose significantly (p less than 0.02) from 29.7 +/- 4.6 (SE) pg/ml in the basal period to to 46.8 +/- 7.1 at the end of the infusion in the pubertal girls but were unchanged in the prepubertal girls. Estrone (E1), progesterone (P), 17-HYDROXYPROGESTERONE (17OHP), TESTOSTERONE (T), DIHYDROTESTOSTERONE (DHT), and androstenedione (A), dehydroepiandrosterone (DHA) and dehydroepiandrosterone sulfate (DHAS) levels were not altered in either maturity group. Basal plasma E2, E1, T, DHT, DHA and DHAS concentrations significantly correlated with the releasable pool of LH evoked by Gn-RH from the pituitary gonadotropes. We conclude: 1) The ovary is not highly and rapidly responsive to transient elevations of endogenous gonadotropin, and 2) Adrenal androgens may to some extent modulate the maturation of the hypothalamic-pituitary-gonadal system, at least as reflected by the pituitary response to exogenous Gn-RH. 相似文献
244.
Douglas E. Biancur Kevin S. Kapner Keisuke Yamamoto Robert S. Banh Jasper E. Neggers Albert S.W. Sohn Warren Wu Robert T. Manguso Adam Brown David E. Root Andrew J. Aguirre Alec C. Kimmelman 《Cell metabolism》2021,33(1):199-210.e8
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245.
246.
To see whether plasma glucose or insulin changed in anticipation of feeding, we provided seven rhesus monkeys with four-hour access to food every other day. Blood was sampled before and during a 30-minute signal which ended with food availability and before and during a 30-minute signal which was not closely and reliably linked with food availability. Plasma insulin showed no evidence of conditioning. Plasma glucose was higher during the signal than prior to the signal in both experiments. This probably reflects the arousing nature of the signal rather than appetitive-associated learning. However, the differences, while statistically significant, were probably biologically trivial because they fall within the normal fluctuations of meal-fed monkeys. Under the conditions of this experiments, it appears that conditional changes in glucose and insulin do not reliably occur in monkeys anticipating access to food. 相似文献
247.
The spectrum of mutations in TBX3: Genotype/Phenotype relationship in ulnar-mammary syndrome. 总被引:6,自引:0,他引:6
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248.
The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus 总被引:1,自引:0,他引:1
Padgett RW; Loeb DD; Snyder LR; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1987,4(1):30-45
Recombinant DNA clones have been isolated that contain 80 kb of the
beta-globin complex from the deer mouse, Peromyscus maniculatus.
Comparisons of this complex with that from the laboratory mouse, Mus
domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3,
Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin
complex since the two species diverged. Unlike other mammals studied thus
far, the deer mouse possesses three adult genes. Partial sequence analysis
indicates that each of the three adult genes is intact and hence may be
functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to
genomic blots from Peromyscus reveals that it has a homologous counterpart
in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO
and Hbb-bhl, are also found in Peromyscus. The strong hybridization between
the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO
genes suggest that both pairs are important for the ontogeny of these mice
although no known product has been identified for the Hbb-bhO genes. The
presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication
that created this related gene set occurred before the two lineages
diverged. A single gene for Hbb-y has been isolated from Peromyscus. The
adult region in Peromyscus has undergone significant divergence from the
same region in Mus, having three rather than two adult genes, the
acquisition of at least 15 kb of extra DNA relative to Mus, and possibly
the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in
contrast, contains the same set of genes apparently distributed over the
same amount of DNA as in the Mus beta- globin complex. This observation
suggests that the embryonic region of the complex is more evolutionarily
stable than the adult region.
相似文献
249.
250.