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101.
旱地玉米农田棵间蒸发研究 总被引:3,自引:0,他引:3
采用中子微区模拟装置测量旱地玉农田棵间蒸发,实验表明,本实验装置实用可行。晋西棵间蒸发量占降水量(510nm)的55%以上,棵间蒸发与蒸散的比值同时叶面积指数呈反相关,玉米产量与作物蒸腾呈正相关。 相似文献
102.
Novel nuclear ribonucleoprotein structural components in the dormouse adrenal cortex during hibernation 总被引:4,自引:0,他引:4
Manuela Malatesta Carlo Zancanaro Monica Tamburini Terence E. Martin Xiang-Dong Fu Peter Vogel Stanislav Fakan 《Chromosoma》1995,104(2):121-128
Adrenocortical cell nuclei of the dormouse Muscardinus avellanarius were investigated by electron microscopic immunocytochemistry in hibernating, arousing and euthermic individuals. While the basic structural constituents of the cell nucleus did not significantly were found in nuclei of hibernating dormice. Lattice-like bodies (LBs), clustered granules (CGs), fibrogranular material (FGM) and granules associated with bundles of nucleoplasmic fibrils (NF) all contained ribonucleoproteins (RNPs), as shown by labeling with anti-snRNP (small nuclear RNP), anti-m3G-capped RNA and anti-hnRNP (heterogeneous nuclear RNP) antibodies. Moreover, the FGM also showed immunoreactivity for the proliferation associated nuclear antigen (PANA) and the non-snRNP splicing factor SC-35. All these nuclear structural components disappeared early during arousal and were not found in euthermic animals. These novel RNP-containing structures, which have not been observed in other tissues investigated so far in the same animal model, could represent storage and/or processing sites for pre-mRNA during the extreme metabolic condition of hibernation, to be quickly released upon arousal. NFs, which had been sometimes found devoid of associated granules in nuclei of brown adipose tissue from hibernating dormice, were present in much higher amouts in adrenocortical cell nuclei; they do not contain RNPs and their role remains to be elucidated. The possible roles of these structures are discussed in the frame of current knowledge of morpho-functional relationships in the cell nucleus. 相似文献
103.
H.C. Chan S.H. Law P.S. Leung L.X.M. Fu P.Y.D. Wong 《The Journal of membrane biology》1997,156(3):241-249
The β-adrenergic (cAMP-dependent) regulation of Cl− conductance is defective in cystic fibrosis (CF). The present study explored alternative regulation of anion secretion in
CF pancreatic ductal cells (CFPAC-1) by angiotensin II (AII) using the short-circuit current (I
SC
) technique. An increase in I
SC
could be induced in CFPAC-1 cells by basolateral or apical application of AII in a concentration-dependent manner (EC50 at 3 μm and 100 nm, respectively). Angiotensin receptor subtypes were identified using specific antagonists, losartan and PD123177, for AT1 and AT2 receptors, respectively. It was found that losartan (1 μm) could completely inhibit the AII-induced I
SC
, whereas, PD123177 exerted insignificant effect on the I
SC
, indicating predominant involvement of AT1 receptors. The presence of AT1 receptors in CFPAC-1 cells was also demonstrated by immunohistochemical studies using specific antibodies against AT1 receptors. Confocal microscopic study demonstrated a rise in intracellular Ca2+ upon stimulation by AII indicating a role of intracellular Ca2+ in mediating the AII response. Depletion of intracellular but not extracellular pool of Ca2+ diminished the AII-induced I
SC
. Treatment of the monolayers with a Cl− channel blocker, DIDS, markedly reduced the I
SC
, indicating that a large portion of the AII-activated I
SC
was Cl−-dependent. AII-induced I
SC
was also observed in monolayers whose basolateral membranes had been permeabilized by nystatin, suggesting that the I
SC
was mediated by apical Cl− channels. Our study indicates an AT1-mediated Ca2+-dependent regulatory mechanism for anion secretion in CF pancreatic duct cells which may be important for the physiology
and pathophysiology of the pancreas.
Received: 17 June 1996/Revised: 14 November 1996 相似文献
104.
中国东亚飞蝗新类型蝗区──海南热带稀树草原蝗区的生态地理特征及其与大沙河蝗区比较 总被引:2,自引:0,他引:2
本文系统地对海南热带稀树草原螟区的生态地理结构特征进行了分析,说明本蝗区是Uvarov(1936)提出的飞蝗两类蝗区理论中.由于森林破坏而形成的一类蝗区,作者将它定名为"热带稀树草原蝗区"。这类蝗区在我国过去尚缺乏研究。文中进而根据本蝗区的成因、生态特征以及对蝗区的生态控制对策,分别与我国大陆的东亚飞蝗大沙河类型蝗区进行了比较。 相似文献
105.
106.
综述了近年来有关利用基因转移技术修饰肿瘤细胞制备肿瘤基因工程疫苗的最新研究进展,着重阐述了逆转录病毒载体介导的基因转移及其安全性;归纳了目前可用于肿瘤基因工程疫苗的各种目的基因的特点及作用并对这类肿瘤疫苗制备过程中所存在的问题进行了分析. 相似文献
108.
溶剂极性及盐酸胍对碳酸酐酶构象的影响 总被引:1,自引:0,他引:1
以紫外荧光光谱为检测手段,比较研究了溶剂极性及盐酸胍对碳酸酐酶构象的影响,结果表明,当盐酸胍浓度小于1mol/L时酶呈天然构象,1.5mol/L-2.0mol/L的盐酸胍导致该酶呈伸展构象;而乙醇不以导致该酶产生稳定的中间态构象,1mol/L和3mol/L的甲醇以及3mol/L的乙醇对盐酸胍致碳酸酐酶中间态的影响不大,甲醇略使致中间态的盐酸胍浓度下降,乙醇略使之上升。 相似文献
109.
F.M.A.H. Schuurmans Stekhoven H.G.P. Swarts Y.-F. Fu G.A.J. Kuijpers J.J.H.H.M. de Pont S.L. Bonting 《生物化学与生物物理学报:生物膜》1984,774(2):277-287
(1) Treatment of from rabbit kidney outer medulla with the labeled thio-analogue of ATP in the presence of and the absence of K+ leads to thiophosphorylation of the enzyme. The value for [γ-S]ATP is 2.2 μM and for Na+ 4.2 mM at 22°C. Thiophosphorylation is a sigmoidal function of the Na+ concentration, yielding a Hill coefficient . (2) The thio-analogue () can also support overall activity, but at 37°C is only h?1 or 0.09% of the specific activity for ATP (). (3) The thiophosphoenzyme intermediate, like the natural phosphoenzyme, is sensitive to hydroxylamine, indicating that it also is an acylphosphate. However, the thiophosphoenzyme, unlike the phosphoenzyme, is acid labile at temperatures as low as 0°C. The acid-denatured thiophosphoenzyme has optimal stability at pH 5–6. (4) The thiophosphorylation capacity of the enzyme is equal to its phosphorylation capacity, indicating the same number of sites. Phosphorylation by ATP excludes thiophosphorylation, suggesting that the two substrates compete for the same phosphorylation site. (5) The (apparent) rate constants of thiophosphorylation (0.4 s?1 vs. 180 s?1), spontaneous dethiophosphorylation (0.04 s?1 vs. 0.5 s?1) and K+-stimulated dethiophosphorylation (0.54 s?1 vs. 230 s?1) are much lower than those for the corresponding reactions based on ATP. (6) In contrast to the phosphoenzyme, the thiophosphoenzyme is ADP-sensitive (with an apparent rate constant in ADP-induced dethiophosphorylation of 0.35 s?1, ) and is relatively K+-insensitve. The for K+ in dethiophosphorylation is 0.9 mM and in dephosphorylation 0.09 mM. The thiophosphoenzyme appears to be for 75–90% in the ADP-sensitive E1-conformation. 相似文献
110.
7-Methylbenz[a]anthracene (7-MBA) was metabolized stereoselectively by rat liver microsomes to form five optically active dihydrodiols as the predominant metabolites. The dihydrodiols were purified by a combination of reversed-phase and normal-phase high performance liquid chromatography (HPLC). By comparison of their circular dichroism (CD) spectra with the corresponding benz[a]anthracene (BA) dihydrodiols of known absolute stereochemistry, the major dihydrodiol enantiomers of 7-MBA have been determined to have 1R,2R-, 3R,4R- and 10R , 11R - absolute configurations, respectively. Due to their quasi- diaxial conformations, the absolute configuration of trans-5,6- and trans-8,9-dihydrodiols, the two most abundant metabolites of 7-MBA, could not be determined by simple comparisons of their circular dichroism spectra with those of the quasidi -equatorial BA 5R, 6R - and 8R , 9R -dihydrodiols. The major enantiomers of the quasi- diaxial trans-5,6- and trans-8,9-dihydrodiol metabolites of 7-MBA were determined by comparison to the CD spectrum of 7-bromo-BA 5R, 6R -dihydrodiol and by the exciton chirality method to have R,R absolute stereochemistry. This study also revealed that the circular dichroism Cotton effects of an enantiomeric dihydrodiol of polycyclic aromatic hydrocarbons can be drastically altered if the conformation (quasi- diaxial vs. quasi di-equatorial ) of the dihydrodiol is changed. 相似文献