Nitrate and nitrite transport in bacteria

The topological arrangements of nitrate and nitrite reductases in bacteria necessitate the synthesis of transporter proteins that carry the nitrogen oxyanions across the cytoplasmic membrane. For assimilation of nitrate (and nitrite) there are two types of uptake system known: ABC transporters that are driven by ATP hydrolysis, and secondary transporters reliant on a proton motive force. Proteins homologous to the latter type of transporter are also involved in nitrate and nitrite transport in dissimilatory processes such as denitrification. These proteins belong to the NarK family, which is a branch of the Major Facilitator Superfamily. The mechanism and substrate specificity of transport via these proteins is unknown, but is discussed in the light of sequence analysis of members of the NarK family. A hypothesis for nitrate and nitrite transport is proposed based on the finding that there are two distinct types of NarK.     

Eukaryotic nitrate and nitrite transporters

Nitrate transport is the key step controlling the amount of nitrate incorporated by the cells and subsequent of storage, reduction or export. Molecular, genetic and biochemical approaches to the study of eukaryotic nitrate/nitrite transporters allow an initial understanding of this step, which is much more complex and structured than previously suspected. At the plasma membrane level, two gene families, Nrt1 and Nrt2, account for high- and low-affinity nitrate transporters. Functionality of NRT1 from Arabidopsis and NRT2 proteins from Aspergillus and Chlamydomonas has been demonstrated. However, redundancy of these systems makes it difficult to assign particular physiological roles to each. Data on genes involved in the regulation of nitrate transport and reduction are still scarce. Information on nitrite transporters to the chloroplast is biased by the belief that in vivo nitrous acid diffuses freely to this organellum. The recent progress on these aspects is discussed in this review.     

去甲肾上腺素与内源性阿片肽在兔离体十二指肠电活动中的相互作用

实验采用银质双极电极,记录了家兔离体十二指肠综合肌电,并对去甲肾上腺素(NE)与内源性阿片肽在兔离体十二指肠电活动中的相互作用进行了观察.结果表明:NE 和吗啡对兔离体十二指肠综合肌电峰波簇均有抑制作用,NE 对基本节律无明显影响,而吗啡能使基本节律紊乱、峰电位幅度降低,其作用随剂量增加而变化.纳洛酮可减弱吗啡和 NE 的效应.     

运动应激对大鼠海马去甲肾上腺素、5-羟色胺及前体氨基酸的影响

目的：旨在观察运动应激对海马去甲肾上腺素和5-羟色胺及前体氨基酸的影响。探讨海马对运动应激的反应及运动技能学习的关系。方法：雄性SD大鼠分别直接处死，力竭性跑台运动后即刻和运动后24h处死；高效液相色谱法，测试去甲肾上腺素、5-羟色胺、酪氨酸和色氨酸。结果：与安静组相比，运动后即刻海马内去甲肾上腺素和色氨酸均显著性升高，运动后24h有所下降；安静时大鼠5-羟色胺与色氨酸，及运动后24h去甲肾上腺素、5-羟色胺及其前体氨基酸间的均呈显著性强相关系；安静时去甲肾上腺素与5-羟色胺相关系数也很高，p=0．055。结论：力竭性跑台运动应激过程中，去甲肾上腺素和5-HT参与应激反应，运动应激后的24h，大鼠海马内的去甲肾上腺素、5-羟色胺、酪氨酸和色氨酸含量及相关关系的个体差异减小，可能与运动技能、记忆形成和保持有关。     

动脉血管低温保存后的功能测试

血管的基本功能在冻存后的保持情况对血管移植影响奶大，通过测量冻存前后血管基本功能来判断保存效果的优劣，分别用含不同浓度的去甲肾上腺素或硝普钠的培养液，来测试经不同降温冻存后的血管的收缩功能和舒张功能，以确定降温速率对保持血管基本功能的影响。     

Identification of Ser354 and Ser357 involved in the function of norepinephrine transporter

Conserved Ser 354, Ser 357 in the seventh transmembrane domain of NET were mutated and the function of mutants was studied by 3H-NE influx measurement. Double mutation at these two serine sites reduced the activity of NET to base level. It is inferred that these two sites may be involved in the recognition and transport activity of the NET protein.     

植物钾离子转运相关蛋白及基因研究进展

本文概述了植物体内与K^ 转运相关的蛋白及其基因，包括通道蛋白(channel protein)和转运体(transporter)及其基因,前者可分为：(1)内向整流K^ 通道(inward-rectifying K^ channel:Kin^ )，(2)外向整流K^ 通道(outward-rectifyjng K^ channel ：Kout^ )；相关基因有AKTI，ANTI，SORK，GORK等．后者分为低亲和K^ 吸收转运体及高亲和K^ 吸收转运体；相关基因有HAK，KUP等．     

水稻(Oryza sativa L.)磷酸盐转运蛋白编码基因的表达研究

研究揭示了水稻磷酸盐转运蛋白编码基因的表达．低磷处理下，根系与叶片中的PTW-J，转录子迅速表达，处理7d时达到最高表达量．PTW-J mRNA的诱导积累具有元素的专一性，因为在缺氮、缺钾与缺铁情况下此基因不表达．缺磷处理后恢复供磷，PTW-J转录子积累量明显降低．这些结果说明，PTW-J基因表达是对磷素缺乏的早期反应机制．     

建立一个基于报告基因的靶标筛药系统筛选上调ABCA1基因转录的中药提取物

ATP结合盒转运蛋白A1(ABCA1)具有催化外周细胞过量胆固醇和磷脂外向流出的功能。本实验将ABCA1启动子序列克隆到含有荧光素酶报告基因和新霉素抗性基因的pGL3B-neo载体中,并将得到的重组质粒pGL3B-neo/ABCA1转染入人肝癌细胞(hepG2)。通过稀释培养法最终得到含有重组质粒的稳定细胞系SABCA1。利用这个报告基因为基础的药物筛选系统,筛选了100多种中药提取物。通过荧光素酶活性测试,相对活性达到180%以上的有4种中药提取物,并最终挑选能明显激活ABCA1基因启动子的鬼箭羽水提组分进一步研究,得出半数有效浓度(EC50)为48.06 mg/L。此外,利用基于apoA1基因的药物筛选系统验证得出鬼箭羽水提组分也能促进apoA1基因的表达。     

Lipid flippases and their biological functions

The typically distinct phospholipid composition of the two leaflets of a membrane bilayer is generated and maintained by bi-directional transport (flip-flop) of lipids between the leaflets. Specific membrane proteins, termed lipid flippases, play an essential role in this transport process. Energy-independent flippases allow common phospholipids to equilibrate rapidly between the two monolayers and also play a role in the biosynthesis of a variety of glycoconjugates such as glycosphingolipids, N-glycoproteins, and glycosylphosphatidylinositol (GPI)-anchored proteins. ATP-dependent flippases, including members of a conserved subfamily of P-type ATPases and ATP-binding cassette transporters, mediate the net transfer of specific phospholipids to one leaflet of a membrane and are involved in the creation and maintenance of transbilayer lipid asymmetry of membranes such as the plasma membrane of eukaryotes. Energy-dependent flippases also play a role in the biosynthesis of glycoconjugates such as bacterial lipopolysaccharide. This review summarizes recent progress on the identification and characterization of the various flippases and the demonstration of their biological functions. Received 12 April 2006; received after revision 22 June 2006; accepted 30 August 2006