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排序方式: 共有234条查询结果,搜索用时 15 毫秒
181.
Reversible loss of affinity induced by glucose in the maltose-H+ symport of Saccharomyces cerevisiae 总被引:3,自引:0,他引:3
Glucose represses and inactivates maltose transport in Saccharomyces cerevisiae. The inactivation has been described as an irreversible process involving proteolysis. We have studied the inactivation of the maltose-H+ symport in this yeast and have observed that the mechanism of inactivation depends on the physiological conditions. In resting cells there was a decrease in transport capacity. The rate of decrease was enhanced nonspecifically by the presence of a sugar, glucose being more effective than maltose. In growing cells, glucose induced a decrease in affinity of the H+-symport which could be recovered by starvation, even in the presence of cycloheximide; there was no loss in capacity or, if present, this loss could be explained fully by the dilution due to repression during growth on glucose. We submit that in growing cells inactivation consists in a reversible modification of the permease not involving proteolysis. 相似文献
182.
Effect of growth rate and aeration on the production of microcin by Escherichia coli growing in continuous culture 总被引:1,自引:0,他引:1
The production of microcin 15, a low molecular weight antibiotic, resistant to proteases and antagonized by methionine, was measured in batch and continuous cultures of E. coli LP 136. The highest yield per cell was obtained in conditions (anaerobiosis, low glucose concentration, low growth rate) similar to those found in the intestinal tract. It is postulated that microcin production may be an important factor in growth competition between enterobacteria in the intestinal tract. 相似文献
183.
M. Peinado M. Á. Macías F. M. Ocaña-Peinado J. L. Aguirre J. Delgadillo 《Plant Ecology》2011,212(2):263-281
We describe relationships between the bioclimates and vegetation of the northwest of Mexico, including the Baja California
peninsula and the stretch of the Pacific basin between the states of Sonora and Colima, a transition zone from the most arid
deserts of North America to tropical rainforests. Links were inferred from temperature and rainfall data obtained from 453
weather stations that were used to construct climatograms, calculate several climate indices and describe main latitudinal
and longitudinal trends, and from sampling the vegetation around these stations. Across this extensive area, spanning some
14° of both latitude and longitude as well as three zonobiomes and two zonoecotones, two macrobioclimates were identified,
Mediterranean and Tropical, within which we were able to distinguish six bioclimates. For each of these bioclimates, we find
different types of zonal and azonal vegetation, whose floristic composition and physiognomy are described here. 相似文献
184.
Igor Y Oshkin David AC Beck Andrew E Lamb Veronika Tchesnokova Gabrielle Benuska Tami L McTaggart Marina G Kalyuzhnaya Svetlana N Dedysh Mary E Lidstrom Ludmila Chistoserdova 《The ISME journal》2015,9(5):1119-1129
We report observations on the dynamics of bacterial communities in response to methane stimulus in laboratory microcosm incubations prepared with lake sediment samples. We first measured taxonomic compositions of long-term enrichment cultures and determined that, although dominated by Methylococcaceae types, these cultures also contained accompanying types belonging to a limited number of bacterial taxa, methylotrophs and non-methylotrophs. We then followed the short-term community dynamics, in two oxygen tension regimens (150 μM and 15 μM), observing rapid loss of species diversity. In all microcosms, a single type of Methylobacter represented the major methane-oxidizing partner. The accompanying members of the communities revealed different trajectories in response to different oxygen tensions, with Methylotenera species being the early responders to methane stimulus under both conditions. The communities in both conditions were convergent in terms of their assemblage, suggesting selection for specific taxa. Our results support prior observations from metagenomics on distribution of carbon from methane among diverse bacterial populations and further suggest that communities are likely responsible for methane cycling, rather than a single type of microbe. 相似文献
185.
186.
Garzón-Alvarado DA Peinado Cortés LM Cárdenas Sandoval RP 《Computer methods in biomechanics and biomedical engineering》2011,14(1):23-32
This paper introduces a 'hypothesis about the growth pattern of the secondary ossification centre (SOC)', whereby two phases are assumed. First, the formation of cartilage canals as an event essential for the development of the SOC. Second, once the canals are merged in the central zone of the epiphysis, molecular factors are released (primarily Runx2 and MMP9) spreading and causing hypertrophy of adjacent cells. In addition, there are two important molecular factors in the epiphysis: PTHrP and Ihh. The first one inhibits chondrocyte hypertrophy and the second helps the cell proliferation. Between these factors, there is negative feedback, which generates a highly localised and stable pattern over time. From a mathematical point of view, this pattern is similar to the patterns of Turing. The spread of Runx2 hypertrophies the cells from the centre to the periphery of the epiphysis until found with high levels of PTHrP to inhibit hypertrophy. This mechanism produces the epiphyseal bone-plate. Moreover, the hypertrophy is inhibited when the cells sense low shear stress and high pressure levels that maintain the articular cartilage structure. To test this hypothesis, we solve a system of coupled partial differential equations using the finite element method and we have obtained spatio-temporal patterns of the growth process of the SOC. The model is in qualitative agreement with experimental results previously reported by other authors. Thus, we conclude that this model can be used as a methodological basis to present a complete mathematical model of the whole epiphyseal development. 相似文献
187.
Peinado JR Quirós PM Pulido MR Mariño G Martínez-Chantar ML Vázquez-Martínez R Freije JM López-Otín C Malagón MM 《Molecular & cellular proteomics : MCP》2011,10(11):M111.008094
Lipodystrophy is a major disease involving severe alterations of adipose tissue distribution and metabolism. Mutations in genes encoding the nuclear envelope protein lamin A or its processing enzyme, the metalloproteinase Zmpste24, cause diverse human progeroid syndromes that are commonly characterized by a selective loss of adipose tissue. Similarly to humans, mice deficient in Zmpste24 accumulate prelamin A and display phenotypic features of accelerated aging, including lipodystrophy. Herein, we report the proteome and phosphoproteome of adipose tissue as well as serum metabolome in lipodystrophy by using Zmpste24(-/-) mice as experimental model. We show that Zmpste24 deficiency enhanced lipolysis, fatty acid biogenesis and β-oxidation as well as decreased fatty acid re-esterification, thus pointing to an increased partitioning of fatty acid toward β-oxidation and away from storage that likely underlies the observed size reduction of Zmpste24-null adipocytes. Besides the mitochondrial proteins related to lipid metabolism, other protein networks related to mitochondrial function, including those involved in tricarboxylic acid cycle and oxidative phosphorylation, were up-regulated in Zmpste24(-/-) mice. These results, together with the observation of an increased mitochondrial response to oxidative stress, support the relationship between defective prelamin A processing and mitochondrial dysfunction and highlight the relevance of oxidative damage in lipoatrophy and aging. We also show that absence of Zmpste24 profoundly alters the processing of the cytoskeletal protein vimentin and identify a novel protein dysregulated in lipodystrophy, High-Mobility Group Box-1 Protein. Finally, we found several lipid derivates with important roles in energy balance, such as Lysophosphatidylcholine or 2-arachidonoylglycerol, to be dysregulated in Zmpste24(-/-) serum. Together, our findings in Zmpste24(-/-) mice may be useful to unveil the mechanisms underlying adipose tissue dysfunction and its overall contribution to body homeostasis in progeria and other lipodystrophy syndromes as well as to develop novel strategies to prevent or ameliorate these diseases. 相似文献
188.
Scott A. Reid Jinguang Zhang Grace L. Anderson Jessica Gasiorek Douglas Bonilla Susana Peinado 《Evolution and human behavior》2012,33(5):471-478
To avoid disease, people should maintain close ties with ingroup members but maintain distance from outgroup members who possess novel pathogens. Consistent with this disease-avoidance hypothesis, pathogenic stimuli, as well as increased personal vulnerability to disease, are associated with xenophobic and ethnocentric attitudes. Researchers assume that this disease-avoidance process is an automatic emotional response that compels negative attitudes and behavioral avoidance. However, when outgroup contact can represent fitness costs or benefits, and when group membership is an uncertain cue to infection risk, it becomes a fitness advantage for a social perceiver to track group membership and thus infection risk. Given that accents can be a cue to group membership, we predicted that the perception of linguistic similarity to ingroup speakers and dissimilarity from outgroup speakers would increase with individual differences in pathogen disgust, and that this association would be most apparent when threat of disease was salient. This hypothesis was confirmed in two experiments. Further, the mechanism was domain specific—disgust due to sexual acts and moral violations did not moderate perceived linguistic distance. The disease-avoidance mechanism is not just an automatic disgust-based reaction; it also operates through the cognitive appraisal of social distance. 相似文献
189.
Lima-Costa ME Tavares C Raposo S Rodrigues B Peinado JM 《Journal of industrial microbiology & biotechnology》2012,39(5):789-797
The waste materials from the carob processing industry are a potential resource for second-generation bioethanol production. These by-products are small carob kibbles with a high content of soluble sugars (45–50%). Batch and fed-batch Saccharomyces cerevisiae fermentations of high density sugar from carob pods were analyzed in terms of the kinetics of sugars consumption and ethanol inhibition. In all the batch runs, 90–95% of the total sugar was consumed and transformed into ethanol with a yield close to the theoretical maximum (0.47–0.50 g/g), and a final ethanol concentration of 100–110 g/l. In fed-batch runs, fresh carob extract was added when glucose had been consumed. This addition and the subsequent decrease of ethanol concentrations by dilution increased the final ethanol production up to 130 g/l. It seems that invertase activity and yeast tolerance to ethanol are the main factors to be controlled in carob fermentations. The efficiency of highly concentrated carob fermentation makes it a very promising process for use in a second-generation ethanol biorefinery. 相似文献
190.
Salima FE van Weely J Christiaan van Denderen Martijn PM Steultjens Marike van der Leeden Michael T Nurmohamed Joost Dekker Ben AC Dijkmans Irene E van der Horst-Bruinsma 《Arthritis research & therapy》2012,14(2):R52-6