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1.
Evidence for an ascorbate shuttle for the transfer of reducing equivalents across chromaffin granule membranes 总被引:2,自引:0,他引:2
Adrenal chromaffin granules must shuttle reducing equivalents from the cytosol inward to reduce ascorbic acid oxidized during norepinephrine biosynthesis by intragranular dopamine-beta-hydroxylase. A transmembrane electron shuttle between the external (cytosolic) and intragranular ascorbate pools was demonstrated in vitro in intact bovine chromaffin granules undergoing tyramine- or dopamine-stimulated dopamine-beta-hydroxylase turnover. Incubation of intact chromaffin granules with tyramine results in a time-dependent decrease in reduced intragranular ascorbate and production of octopamine. The rate of ascorbate oxidation is a function of the extragranular concentrations of tyramine over the range 50 microM to 2 mM and is 95% inhibited by addition of the dopamine-beta-hydroxylase inhibitor disulfiram. The stoichiometry of octopamine synthesized/ascorbate oxidized closely approximates unity. The presence of extragranular dopamine also induces oxidation of intragranular ascorbate which is inhibited by blocking dopamine transport with reserpine. On the other hand, incubation with octopamine, which is also transported by the granules, causes no net decrease in reduced intragranular ascorbate. The presence of 400 microM extragranular ascorbate abolishes the observed tyramine-induced intragranular ascorbate oxidation. The addition of ascorbate extragranularly 30 min after addition of tyramine reverses the oxidation of intragranular ascorbate. The measurement of [14C]ascorbate distribution ratios in granule pellets and supernatants indicates that there is no transmembrane transport of ascorbate. Extravesicular NADH had no significant effect on matrix ascorbate levels during beta-hydroxylation. These data provide new in vitro evidence that chromaffin granules shuttle reducing equivalents inwardly from an extra- to an intravesicular ascorbate pool and that cytosolic ascorbate is the source of the intragranular reducing equivalents required during norepinephrine biosynthesis. 相似文献
2.
For several species of lepidoptera, most of the approximately 350-bp
mitochondrial control-region sequences were determined. Six of these
species are in one genus, Jalmenus; are closely related; and are believed
to have undergone recent rapid speciation. Recent speciation was supported
by the observation of low interspecific sequence divergence. Thus, no
useful phylogeny could be constructed for the genus. Despite a surprising
conservation of control-region length, there was little conservation of
primary sequences either among the three lepidopteran genera or between
lepidoptera and Drosophila. Analysis of secondary structure indicated only
one possible feature in common--inferred stem loops with higher-than-random
folding energies-- although the positions of the structures in different
species were unrelated to regions of primary sequence similarity. We
suggest that the conserved, short length of control regions is related to
the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In
addition, determination of flanking sequences for one Jalmenus species
indicated (i) only weak support for the available model of insect 12S rRNA
structure and (ii) that tRNA translocation is a frequent event in the
evolution of insect mitochondrial genomes.
相似文献
3.
A cell culture assay for follicle-stimulating hormone 总被引:3,自引:0,他引:3
Cultured rat ovarian granulosa cells respond to follicle-stimulating hormone (FSH) by synthesizing and secreting plasminogen activator. The specificity of the response for FSH prompted us to explore the use of this system as an in vitro bioassay for FSH. The release of FSH by pituitary cell cultures has been examined by this method, as have been preparations of FSH of known biological activity. The results indicate that the granulosa cell system allows accurate, rapid, and convenient determinations of FSH activity. Furthermore, the method obviates metabolic clearance problems associated with whole animal assays and it is extremely sensitive: as little as 10(-15) mol (approximately 100 micronIU) of FSH can be detected. 相似文献
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Sophie O. Vanwambeke Eric F. Lambin Markus P. Eichhorn Stéphane P. Flasse Ralph E. Harbach Linda Oskam Pradya Somboon Stella van Beers Birgit H. B. van Benthem Cathy Walton Roger K. Butlin 《EcoHealth》2007,4(1):37-51
Land-use change, a major constituent of global environmental change, potentially has significant consequences for human health
in relation to mosquito-borne diseases. Land-use change can influence mosquito habitat, and therefore the distribution and
abundance of vectors, and land use mediates human–mosquito interactions, including biting rate. Based on a conceptual model
linking the landscape, people, and mosquitoes, this interdisciplinary study focused on the impacts of changes in land use
on dengue and malaria vectors and dengue transmission in northern Thailand. Extensive data on mosquito presence and abundance,
land-use change, and infection risk determinants were collected over 3 years. The results of the different components of the
study were then integrated through a set of equations linking land use to disease via mosquito abundance. The impacts of a
number of plausible scenarios for future land-use changes in the region, and of concomitant behavioral change were assessed.
Results indicated that land-use changes have a detectable impact on mosquito populations and on infection. This impact varies
according to the local environment but can be counteracted by adoption of preventive measures. 相似文献
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MF Perutz 《Current opinion in structural biology》1996,6(6):848-858
Several dominantly inherited, late onset, neurodegenerative diseases are due to expansion of CAG repeats, leading to expansion of glutamine repeats in the affected proteins. These proteins are of very different sizes and, with one exception, show no sequence homology to known proteins or to each other; their functions are unknown. In some, the glutamine repeat starts near the N-terminus, in another near the middle and in another near the C-terminus, but regardless of these differences, no disease has been observed in individuals with fewer than 37 repeats, and absence of disease has never been found in those with more than 41 repeats. Protein constructs with more than 41 repeats are toxic to E. coli and to CHO cells in culture, and they elicit ataxia in transgenic mice. These observations argue in favour of a distinct change of structure associated with elongation beyond 37–41 glutamine repeats. The review describes experiments designed to find out what these structures might be and how they could influence the properties of the proteins of which they form part. Poly-
-glutamines form pleated sheets of β-strands held together by hydrogen bonds between their amides. Incorporation of glutamine repeats into a small protein of known structure made it associate irreversibly into oligomers. That association took place during the folding of the protein molecules and led to their becoming firmly interlocked by either strand- or domain-swapping. Thermodynamic considerations suggest that elongation of glutamine repeats beyond a certain length may lead to a phase change from random coils to hydrogen-bonded hairpins. Possible mechanisms of expansion of CAG repeats are discussed in the light of looped DNA model structures. 相似文献
9.
Programmed cell death during plant growth and development 总被引:12,自引:0,他引:12
Beers EP 《Cell death and differentiation》1997,4(8):649-661
This review describes programmed cell death as it signifies the terminal differentiation of cells in anthers, xylem, the suspensor and senescing leaves and petals. Also described are cell suicide programs initiated by stress (e.g., hypoxia-induced aerenchyma formation) and those that depend on communication between neighboring cells, as observed for incompatible pollen tubes, the suspensor and synergids in some species. Although certain elements of apoptosis are detectable during some plant programmed cell death processes, the participation of autolytic and perhaps autophagic mechanisms of cell killing during aerenchyma formation, tracheary element differentiation, suspensor degeneration and senescence support the conclusion that nonapoptotic programmed cell death pathways are essential to normal plant growth and development. Heterophagic elimination of dead cells, a prominent feature of animal apoptosis, is not evident in plants. Rather autolysis and autophagy appear to govern the elimination of cells during plant cell suicide. 相似文献
10.