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61.
62.
Ultrastructural correlation of water reabsorption in isolated rat cauda epididymidis 总被引:2,自引:0,他引:2
Electron microscopic study was made on the water reabsorption of the epithelial cells of the rat cauda epididymidis. It was shown that when the epididymal duct was reabsorbing water at a maximal rate, widely dilated intercellular spaces were seen. It is suggested that the standing gradient model of water reabsorption first proposed for the gall bladder may also operate in the cauda epididymidis. 相似文献
63.
Acetylcholine activates both nicotinic and muscarinic receptors in the central nervous system. Although the action of acetylcholine at muscarinic receptor has been well characterized, relatively little is known at the cellular level concerning nicotinic receptor stimulation in brain. Central nicotinic receptors have been implicated in Alzheimer's disease, seizure activity, the generation of slow-wave theta rhythm in the hippocampus and the potential abuse liability of nicotine. At the neuronal level, nicotinic agonists have been most often associated with postsynaptically mediated excitation and membrane depolarization at various sites, including Renshaw spinal motoneurons, locus coeruleus and the medial habenular nucleus. Nicotine acting presynaptically can produce either excitation or inhibition indirectly through the release of endogeneous transmitters or modulators. Whereas a direct inhibitory effect of nicotine has been suggested by one in vivo extracellular recording study in rat cerebellar Purkinje neurons, the mechanism(s) underlying this action is not yet known. We now report our findings obtained using in vitro intracellular methods in a submerged brain slice preparation in which application of nicotinic agonists to rat dorsolateral septal neurons reveal a direct membrane hyperpolarization mediated by an increase in potassium conductance. 相似文献
64.
J Kuriyan T S Krishna L Wong B Guenther A Pahler C H Williams P Model 《Nature》1991,352(6331):172-174
An example of two related enzymes that catalyse similar reactions but possess different active sites is provided by comparing the structure of Escherichia coli thioredoxin reductase with glutathione reductase. Both are dimeric enzymes that catalyse the reduction of disulphides by pyridine nucleotides through an enzyme disulphide and a flavin. Human glutathione reductase contains four structural domains within each molecule: the flavin-adenine dinucleotide (FAD)- and nicotinamide-adenine dinucleotide phosphate (NADPH)-binding domains, the 'central' domain and the C-terminal domain that provides the dimer interface and part of the active site. Although both enzymes share the same catalytic mechanism and similar tertiary structures, their active sites do not resemble each other. We have determined the crystal structure of E. coli thioredoxin reductase at 2 A resolution, and show that thioredoxin reductase lacks the domain that provides the dimer interface in glutathione reductase, and forms a completely different dimeric structure. The catalytically active disulphides are located in different domains on opposite sides of the flavin ring system. This suggests that these enzymes diverged from an ancestral nucleotide-binding protein and acquired their disulphide reductase activities independently. 相似文献
65.
The Oct4 and Nanog transcription network regulates pluripotency in mouse embryonic stem cells 总被引:45,自引:0,他引:45
66.
Xiaofeng Xia Shaoxiong Wang Jianbang Luo Ricky N. S. Wong Senfang Sui 《科学通报(英文版)》1999,44(20):1892-1892
Tianhuafen is a kind of traditional Chinese medicine for abortion, which has long been used in China. The basic protein trichosanthin (TCS) is responsible for such activity. As a ribosome inactivating protein (RIP), trichosanthin removes A4304 in the 28s rRNA via the N-glycosidase activity and inactivates the ribosome. However, it remains unclear how TCS can enter the cytoplasm. In the experiment, monolayers at air/water interface have been used to study the interaction between TCS and phospholipid membrane. The results show that TCS can penetrate negatively charged phospholipid monolayer under acid condition, and its membrane penetrating ability is obviously pH-dependent. A hypothesis of TCS penetrating biological membrane under acid condition is proposed based on the obtained result. 相似文献
67.
Directional guidance of neuronal migration in the olfactory system by the protein Slit. 总被引:34,自引:0,他引:34
Although cell migration is crucial for neural development, molecular mechanisms guiding neuronal migration have remained unclear. Here we report that the secreted protein Slit repels neuronal precursors migrating from the anterior subventricular zone in the telencephalon to the olfactory bulb. Our results provide a direct demonstration of a molecular cue whose concentration gradient guides the direction of migrating neurons. They also support a common guidance mechanism for axon projection and neuronal migration and suggest that Slit may provide a molecular tool with potential therapeutic applications in controlling and directing cell migration. 相似文献
68.
王永初 《华侨大学学报(自然科学版)》1987,(2):176-180
极值调节器是DDZ-Ⅲ型或DDZ-Ⅱ型系列仪表的一个新单元,可用于生产过程的静态最佳控制,如燃烧效率控制、蒸发器最佳液位控制,由于本调节器是由模拟线路构成,所以在模拟信号的保持,传送以及梯度方向的判断遇到某些困难,本文介绍这些问题及其解决办法。这台仪表的精度为±0.5%。 相似文献
69.
合成了通式为(C15H15N2O3)xRE(NO3)y(H2O)z(当RE=La~Pr时,x=3,y=6,z=0;RE=Nd时,x=2,y=5,z=1;RE=Sm~Lu,Y时,x=2,y=5,z=0)的一系列15种标题配合物.通过元素分析,IR,UV,1HNMR,TG-DTA,摩尔电导和X射线粉末衍射分析等对配合物的性质进行了表征.认为可能生成包含一分子水的11配位钕配合物的原因在于抗衡阳离子的空间效应,使其与络阴离子间的vanderWaals力增强的结果 相似文献
70.
YAO YingMing SHEN Qi WONG Wing Tak 《科学通报(英文版)》2007,52(4):467-470
The lanthanide coordination polymers bearing a 13-membered macrocycle, [(13-EDTA-pnOH)H2] were synthesized. The products [Ln(13-EDTA-pnOH)(H2O)2·NO3]n (Ln = Eu(1), Tb(2), Dy(3)) have been obtained by MS, IR and element analyses. The solid-state structure of 1 was established by single-crystal X-ray analysis. The coordination geometry around the central metal atom in complex 1 is a nine-coor-dinated, tricapped-trigonal prism having six donor atoms (two amine nitrogen atoms, two amide oxygen atoms and two carboxymethyl oxygen atoms) from one ligand, one oxygen atom from a neighboring ligand, and two more oxygen atoms from two water molecules. The europium atoms are linked by―Eu―O―C―O―Eu―bridges to form an infinite chain. 相似文献