敌百虫对水丝蚓的毒害

采用急性毒性方法测定了被不同浓度敌百虫毒害的水丝蚓(Limnodilus hoffineisteri)半致死浓度(LC50),利用测定酶活性方法检测了水丝蚓超氧化物歧化酶(SOD)的变化及中毒后水丝蚓喂饲的强壮水螅(Hydra robusta)SOD的改变。(1)敌百虫对水丝蚓48 h LC50为3.29 mg/L。敌百虫对水丝蚓SOD活性影响显著(P<0.05):在低浓度1~4 mg/L时,SOD活性呈上升趋势,但随浓度增加至5 mg/L,SOD活性开始下降。(2)用1~8 mg/L中毒后的水丝蚓依次喂饲水螅,SOD活性呈上升趋势。实验结果表明,敌百虫作为重要的杀虫剂或作为防治鱼病的药物,对水丝蚓造成胁迫,并在一定浓度范围内直接或间接地影响以其为食的动物的生存,以至危害生命。     

Evidence for direct roles of two additional factors, SECp43 and soluble liver antigen, in the selenoprotein synthesis machinery

Selenocysteine (Sec) is inserted into selenoproteins co-translationally with the help of various cis- and trans-acting factors. The specific mechanisms of Sec biosynthesis and insertion into protein in eukaryotic cells, however, are not known. Two proteins, SECp43 and the soluble liver antigen (SLA), were previously reported to interact with tRNA([Ser]Sec), but their functions remained elusive. Herein, we report that knockdown of SECp43 in NIH3T3 or TCMK-1 cells using RNA interference technology resulted in a reduction in the level of methylation at the 2'-hydroxylribosyl moiety in the wobble position (Um34) of Sec tRNA([Ser]Sec), and consequently reduced glutathione peroxidase 1 expression. Double knockdown of SECp43 and SLA resulted in decreased selenoprotein expression. SECp43 formed a complex with Sec tRNA([Ser]Sec) and SLA, and the targeted removal of one of these proteins affected the binding of the other to Sec tRNA([Ser]Sec). SECp43 was located primarily in the nucleus, whereas SLA was found in the cytoplasm. Co-transfection of both proteins resulted in the nuclear translocation of SLA suggesting that SECp43 may also promote shuttling of SLA and Sec tRNA([Ser]Sec) between different cellular compartments. Taken together, these data establish the role of SECp43 and SLA in selenoprotein biosynthesis through interaction with tRNA([Ser]Sec) in a multiprotein complex. The data also reveal a role of SECp43 in regulation of selenoprotein expression by affecting the synthesis of Um34 on tRNA([Ser]Sec) and the intracellular location of SLA.     

细菌质粒的消除

利用化学消除剂或改变生长条件可以消除细菌中的质粒,除宿主菌的特性及其所含质粒分子量大小之外,消除率还与消除剂浓度,作用时间有关,嵌合染料适用于消除大肠杆菌中的质粒,十二烷基硫酸钠对具有性纤毛的细菌作用效果较好,适当提高培养温度可消除一些细菌中的质粒,胸腺嘧啶限量法仅适用于其营养缺陷菌株的质粒消除,利用原生质体的形成与再生及反复冻融菌体均可消除细菌中的质粒。     

农牧交错区不同植物群落土壤呼吸的日动态观测与测定方法比较

 采用动态密闭气室法（IRGA）对农牧交错区10种植物群落最大生物量时期的土壤呼吸日动态进行了测定,并将该方法得到的土壤日呼吸速率与碱液吸收法（AA）进行了比较。结果表明：1）10个群落土壤呼吸的昼夜变化比较明显,均为单峰型曲线,主要受土壤温度的驱动,但同时也受到当日降水情况和云量、风速等气象因子的较大影响。因此,这些群落土壤呼吸日动态的一致性较差,规律性并不明显。2）用碱液吸收法和动态密闭气室法测定的10个群落的土壤呼吸速率变化范围分别为394～894 mg C·m-2·d-1和313～2043 mg C·m-2·d-1,其中碱液吸收法测定结果平均为动态气室法的67.5%,明显低于动态密闭气室法。3）两种测定方法具有很好的相关性,R2为0.873 9。本研究中发现,在土壤呼吸速率低的情况下,两种方法的测定结果十分接近甚至碱液吸收法测定结果稍大于动态密闭气室法,而在土壤呼吸速率较高的情况下,动态密闭气室法测定结果则显著高于碱液吸收法。上述结果与国内外同类研究的结果高度一致,从而为校正以往采用碱液吸收法在该区域的测定结果提供了可靠依据。     

丛枝菌根真菌对滨梅扦插苗生根、生长和抗病相关酶活性的影响

研究Glomus mosseae,G.diaphanum和G.etunicatum对滨梅插条生根、生长和抗病相关酶活性的影响.结果表明:G.mosseae侵染导致最高生根百分率(47.6%),最多次生细根(20.4条),最高的根干重(0.26 g),最高的地上部分干重(3.55 g),最高的幼苗高度(51.3 cm)及...     

高温胁迫对花生幼苗光合速率、叶绿素含量、叶绿体Ca2+-ATPase、Mg2+-ATPase及Ca2+分布的影响

将水培后盆栽的花生幼苗,置于培养箱42℃高温培养,定时测定幼苗叶光合速率、叶绿素含量和叶绿体Ca2 -ATPase、Mg2 -ATPase的相对活性,并观察幼叶细胞内Ca2 分布的变化。试验结果表明:高温胁迫过程中,光合速率及叶绿素含量都随处理时间的延伸而下降,并呈显著正相关;叶绿体Ca2 -ATPase和Mg2 -ATPase高温胁迫过程中相对活性呈先升后降趋势,Ca2 -ATPase热敏性高于Mg2 -ATPase;高温胁迫过程中,Ca2 具有从胞外转运到胞质内和叶绿体中的趋势,Ca2 能够稳定高温胁迫下叶肉细胞膜和叶绿体的超微结构。     

成体干细胞的可塑性研究进展

人们传统观念认为成体干细胞局限于生成它们所在组织的分化细胞类型。但近年来的实验结果表明,从一个组织来的成体干细胞能被诱导分化成另外的一个组织的分化细胞,即成体干细胞具有可塑性。在此,我们对成体干细胞可塑性的证据、几种假设、调控机制和应用前景等方面做一综述。     

Four New Polyhydroxy Cyclohexanes from the Stems of Fissistigma tientangense

Four undescribed polyhydroxy cyclohexanes, fissoxhydrylenes A–D ( 1–4 ), together with two known biogenetically related polyhydroxy cyclohexanes ( 5 and 6 ) were isolated from the stems of Fissistigma tientangense Tsiang et P. T. Li. Their structures were elucidated by detailed analysis of NMR, HR-ESI-MS, IR, UV and Optical rotations data. The absolute configuration of 1 was confirmed by X-ray crystallographic. The absolute configurations of 2–4 were confirmed by chemical reaction and optical rotations. Compound 4 represent the first example of a no substituent polyhydroxy cyclohexanes from natural products. All isolated compounds were evaluated for their anti-inflammatory activities against the lipopolysaccharide-induced nitric oxide (NO) production in mouse macrophage RAW 264.7 cells in vitro. Compounds 3 and 4 showed inhibitory activities with the IC₅₀ values of 16.63±0.06 μM and 14.38±0.08 μM, respectively.     

Compartmentalization of the Edinburgh Human Metabolic Network

Background  

Direct in vivo investigation of human metabolism is complicated by the distinct metabolic functions of various sub-cellular organelles. Diverse micro-environments in different organelles may lead to distinct functions of the same protein and the use of different enzymes for the same metabolic reaction. To better understand the complexity in the human metabolism, a compartmentalized human metabolic network with integrated sub-cellular location information is required.     

Unassisted refolding of urea-denatured arginine kinase from shrimp Feneropenaeus chinensis: evidence for two equilibrium intermediates in the refolding pathway

The refolding process and the equilibrium intermediates of urea-denatured arginine kinase (AK) were investigated by 1-anilino-8-naphthalenesulfonate (ANS) intrinsic fluorescence, far-UV circular dichroism (CD), size-exclusion chromatography (SEC), and enzymatic activity. In dilute denaturant, two equilibrium refolding intermediates (I and N') were discovered, and a refolding scheme of urea-denatured AK was proposed. During the refolding of urea-denatured AK, the fluorescence intensity increased remarkably, accompanied by a significant blue shift of the emission maximum and a pronounced increase in molar ellipticity of CD at 222 nm. The first folding intermediate (I) was inactive in urea solution ranging between 2.4 and 3.0 M. The second (N') existed between a 0.4- and 0.8-M urea solution, with slightly increased activity. Neither the blue shift emission maximum nor the molar ellipticity of CD at 222 nm showed significant changes in these two regions. The two intermediates were characterized by monitoring the ANS binding ability in various residual urea solutions, and two peaks of the emission intensity were observed in urea solutions of 0.6 and 2.8 M, respectively. The SEC results indicated that a distribution coefficient (K(D)) platform existed in urea solutions ranging between 2.4 and 3.0 M urea, suggesting that there was a similarly apparent protein profile and size in the urea solution region. The refolding kinetics showed that the urea-denatured AK was in two-phase refolding. Proline isomerization occurred in the unfolding process of AK, which blocked the slow phase of refolding. These results suggested that the refolding process of urea-denatured AK contained at the least two equilibrium refolding intermediates.