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排序方式: 共有114条查询结果,搜索用时 15 毫秒
1.
Structural characterization of myosin from bovine brain 总被引:1,自引:0,他引:1
Myosins isolated from bovine brain, rabbit skeletal muscle, and chicken gizzard smooth muscle and their heavy meromyosin and light meromyosin fractions were studied in the electron microscope by negative staining with uranyl acetate. Under similar conditions of preparation and polymerization, the three myosins formed paracrystals of different structures. The light meromyosin portion of the skeletal muscle myosin also assembled in a different fashion than the brain or smooth muscle light meromyosins; the latter two assembled similarly. The heavy meromyosin portion from each of the three myosins was shown to interact with the actins isolated from each of the three tissue sources by the formation of the characteristic arrowhead patterns with similar periodicities. The brain heavy meromyosin attachment to both skeletal and brain actins was dissociated by ATP. It is suggested that differences in the light meromyosin portions of the three myosins may account in part for their differences in assembly in vivo. 相似文献
2.
Compartmentation of glutamic acid metabolism in brain slices 总被引:12,自引:4,他引:8
— (1) Compartmentation of glutamate metabolism in brain cortex previously observed only in vivo, has now been demonstrated in vitro.This was shown by using [U-14C]aspartate and [U-14C]glutamate as tracer substrates. (2) Preparation and maintenance of the slices at 0° resulted in reversible inhibition of glutamine synthesis. Preincubation at 37° for 10 min or preparation of the slices at room temperature partially overcame this inhibition. (3) Transfer to fresh medium after preincubation had an added stimulatory effect on glutamine synthesis. (4) Incubation in high K+ medium (27 mm ) altered the relative specific activity of glutamine. (5) The data are in keeping with the postulate of the existence of at least two different pools of citric acid cycle intermediates in the cerebral cortex. 相似文献
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4.
The ciliate Mesodinium rubrum has excited considerable interest because it has been reported to contain cryptophycean endoxymbionts which lack nuclei (Taylor et al., 1969, 1971). Hibberd (1977), however, has recently shown that in Mesodinium from the United Kingdom the cryptophycean chloroplasts and mitochondria share a common cytoplasm with an apparent cryptophycean nucleus. This cytoplasm is separated from the ciliate cytoplasm by a single membrane. Here we confirm, through extensive observation including serial sectioning, the presence of multiple, discrete, anucleate chloroplast-mitochondrial complexes in a population of Mesodinium from British Columbia. In addition to the normal ciliate macro- and micronuclei, however, these cells contain a third type of nucleus, possibly of cryptophycean origin, which is apparently in its own membrane-bound cytoplasm. This suggests the possibility of a new type of endosymbiotic organization in which endosymbiont organelles have become separated into discrete cytoplasmic compartments. 相似文献
5.
The structure of the dinoflagellate chromosome is examined using spread whole mounts and serial sectioning. Evidence is presented that the chromosome is composed of a toroidal bundle of DNA strands which is coiled plectonemically into a tight double helix. This structure is apparent in interphase whole-mount chromosomes and by careful analysis of serial sectioning can be shown in all mitotic stages. It is particularly apparent in the arms of replicating Y shaped chromosomes which often uncoil slightly (either naturally or as a result of the fixation used). A model is presented which is based on these results and recent genetic and biochemical data. 相似文献
6.
ZHU Zhaoliang XIONG Zhengqin& XING Guangxi State Key Laboratory of Soil Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing China 《中国科学:生命科学英文版》2005,48(Z2)
Asia is the major consumer of fertilizer nitrogen and energy in the world, and consequently shares a considerable proportion of the world creation of reactive nitrogen (Nr). However, if estimated on per capita basis, Asia is characterized by a lower arable land area, fertilizer nitrogen consumption, energy consumption, and gross domestic product, as well as lower daily protein intake. To meet the increasing needs for food and energy for the growing population combined with the improvement of living standards, Nr will inevitably increase. The present study estimates the creation of Nr and the emissions of various N compounds into environment in Asia currently and in 2030. In comparison with the world averages, the lower fertilizer nitrogen and energy use efficiencies, and the lower use of animal wastes for agriculture imply that there is potential for moderating the increase in Nr and its impacts on the environment. Strategies for moderating the increase are discussed. 相似文献
7.
Dean Frawley Claudio Greco Berl Oakley Mohamed M. Alhussain Alastair B. Fleming Nancy P. Keller
zgür Bayram 《Cellular microbiology》2020,22(6)
For eukaryotes like fungi to regulate biological responses to environmental stimuli, various signalling cascades are utilized, like the highly conserved mitogen‐activated protein kinase (MAPK) pathways. In the model fungus Aspergillus nidulans, a MAPK pathway known as the pheromone module regulates development and the production of secondary metabolites (SMs). This pathway consists five proteins, the three kinases SteC, MkkB and MpkB, the adaptor SteD and the scaffold HamE. In this study, homologs of these five pheromone module proteins have been identified in the plant and human pathogenic fungus Aspergillus flavus. We have shown that a tetrameric complex consisting of the three kinases and the SteD adaptor is assembled in this species. It was observed that this complex assembles in the cytoplasm and that MpkB translocates into the nucleus. Deletion of steC, mkkB, mpkB or steD results in abolishment of both asexual sporulation and sclerotia production. This complex is required for the positive regulation of aflatoxin production and negative regulation of various SMs, including leporin B and cyclopiazonic acid (CPA), likely via MpkB interactions in the nucleus. These data highlight the conservation of the pheromone module in Aspergillus species, signifying the importance of this pathway in regulating fungal development and secondary metabolism. 相似文献
8.
应用电子探针对植物根际和根内营养元素微区分布的探讨 总被引:3,自引:0,他引:3
用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。 相似文献
9.
The effect of the excitotoxin kainic acid on glutamate and glutamine metabolism was studied in cerebellar slices incubated with D-[2-14C]glucose, [U-14C]gamma-aminobutyric acid, [3H]acetate, [U-14C]glutamate, and [U-14C]glutamine as precursors. Kainic acid (1 mM) strongly inhibited the labeling of glutamine relative to that of glutamate from all precursors except [2-14C]glucose and [U-14C]glutamine. Kainic acid did not inhibit glutamine synthetase directly. The data indicate that in the cerebellum kainic acid inhibits the synthesis of glutamine from the small pool of glutamate that is thought to be associated with glial cells. Kainic acid also markedly stimulated the efflux of glutamate from cerebellar slices and this release was not sensitive to tetrodotoxin. Kainic acid stimulated efflux of both glucose- and acetate-labeled glutamate. In contrast, veratridine released glucose-labeled glutamate preferentially via a tetrodotoxin-sensitive mechanism. Kainic acid did not release [U-14C]glutamate from synaptosomal fractions. These results suggest that the bulk of the glutamate released from cerebellar slices by kainic acid comes from nonsynaptic pools. 相似文献
10.
垦殖对新疆绿洲农田土壤有机碳组分及团聚体稳定性的影响 总被引:9,自引:0,他引:9
土壤有机碳是土壤质量变化的重要指标,土壤活性有机碳组分在土壤质量变化方面发挥重要作用。采用有机碳分组技术,研究了干旱荒漠区自然土壤开垦对绿洲农田土壤有机碳活性组分及团聚体稳定性的影响。结果表明:低有机碳含量的自然土壤垦殖后,有利于干旱荒漠区绿洲棉田土壤有机碳的积累,且垦殖(0-5a)增加显著,年均增加在0.65gkg-1以上,上升幅度为76%-286%,5a后维持在相对平衡的水平;土壤活性有机碳、轻组有机碳在垦殖0-5a显著增加,平均增加72%和99%,5a后下降;颗粒有机碳则表现出垦殖0-10a明显增加,增加在275%以上,10a后下降;土壤水稳性团聚体含量随垦殖年限的延长显著增加,0-20a内较自然土壤提高了75%。垦殖可能是干旱区绿洲农田潜在碳汇的重要影响因素;但随垦殖年限延长,土壤有机碳活性组分下降,土壤质量又存在一定的退化风险。 相似文献