Plant thioredoxins: the multiplicity conundrum

Thioredoxins are small proteins distinguished by the presence of a conserved dicysteine active site. In oxidized thioredoxin, the two cysteines form a disulfide bond that is targeted by the enzyme thioredoxin reductase. Together with an electron donor, thioredoxin and thioredoxin reductase form the 'thioredoxin system' that is present in all organisms. Thioredoxins participate in dithiol/disulfide exchange reactions with a large range of cellular substrates. Higher plants possess a very complex thioredoxin profile consisting of at least two different thioredoxin systems that contain distinct, multigenic thioredoxin classes which have different intracellular localizations. In this review we summarise the current state of knowledge regarding the function of plant thioredoxins representing all systems and classes. Received 30 October 2001; received after revision 13 December 2001; accepted 17 December 2001     

NFT栽培下不同营养液对提高蔬菜营养的作用

在营养液膜技术（ＮｕｔｒｉｅｎｔＦｉｌｍＴｅｃｈｉｎｉｑｕｅ简称ＮＦＴ）栽培下，研究不同营养液配方对蔬菜的生理效应和提高某些元素的作用．试验结果表明，在一定的浓度范围内增加营养液中的氮素营养，可促使植株氮素的吸收，加速氮素代谢，促进硝酸还原酶的活力及叶片总氮量的增加．适当增加营养液中Ｚｎ，Ｆｅ，Ｃａ的含量，可促进植株对Ｚｎ，Ｆｅ，Ｃａ的吸收，从而提高植株内人体所必需的微量元素含量，培养优质、富营养卫生的保健蔬菜．     

Digoxin and ouabain increase the synthesis of cholesterol in human liver cells

Digoxin and ouabain are steroid drugs that inhibit the Na⁺/K⁺-ATPase, and are widely used in the treatment of heart diseases. They may also have additional effects, such as on metabolism of steroid hormones, although until now no evidence has been provided about the effects of these cardioactive glycosides on the synthesis of cholesterol. Here we report that digoxin and ouabain increased the synthesis of cholesterol in human liver HepG2 cells, enhancing the activity and the expression of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), the rate-limiting enzyme of the cholesterol synthesis. This effect was mediated by the binding of the sterol regulatory element binding protein-2 (SREBP-2) to the HMGCR promoter, and was lost in cells silenced for SREBP-2 or loaded with increasing amounts of cholesterol. Digoxin and ouabain competed with cholesterol for binding to the SREBP-cleavage-activating protein, and are critical regulators of cholesterol synthesis in human liver cells. Received 10 January 2009; received after revision 11 February 2009; accepted 6 March 2009     

层流剪切力对悬浮培养红豆杉细胞HMGR酶基因转录的影响

以HMGR酶基因为研究对象,采用实时荧光RT-PCR技术,研究了Couette式反应器中0．3 Pa层流剪切力作用后悬浮培养的对数期东北红豆杉细胞HMGR酶基因转录情况．结果显示,在对数生长时期,未经剪切处理的悬浮培养虹豆杉细胞HMGR基因转录水平呈增长趋势,而剪切处理后的悬浮培养红豆杉细胞HMGR基因转录水平则基本保持不变．同时,对相应细胞生物量的测定结果也显示出类似的变化．以上结果说明在对数生长时期施加一定强度的剪切力,将使细胞生长发生停滞,谊生长停滞现象可能与因剪切所引起的HMGR基因转录水平下降有一定相关性．     

溴酸钾-碘离子体系催化动力学电位法测定痕量亚硝酸根

实验中发现NO-2 对KBrO3 氧化I-的反应有很强的催化作用。可用碘离子选择电极跟踪反应过程 ,由此建立了测定痕量NO-2 的新方法。在适宜条件下 ,该指示反应为一级反应 ,反应速度可用电位变化ΔE表示。当时间固定 ,ΔE与NO-2 浓度在 0～ 1 6× 10 -6mol/L范围内呈线性关系 ,检出限为 1 4× 10 -10 mol/L。该方法已用于肉类、蔬菜、粮食和血清中NO-2 的测定 ,得到了可靠结果。     

痕量钴镍的催化极谱同时测定的研究

钴(Ⅱ)镍(Ⅱ)在丁二酮肟、亚硝酸钠、磺基水杨酸和NH_4OH-NH_4CI的溶液中,均能产生相当灵敏的催化波,其峰电位分别为-1.27V(钴)和-1.08V(镍)(Vs,S.C.E).在浓度为1.0×10~(-10)～1.0 ×10~(-6)g/mL(钴)和1.0×10~(-9)～1.0×10~(-6)g/mL(镍)的范围内,峰高与浓度成线性关系.用该方法同时测定了水体中、头发中、高纯氧化铜及钴矿中的痕量钴和镍.还测定了维生素B_(12)和C中的痕量钴.     

土壤中亚硝酸根离子含量的测定

采用可见分光光度法测定土壤中亚硝酸根离子的含量。在浸取土壤后的滤液中加入氢氧化铝共沉淀剂，移取定量的二次滤液在酸性条件下与对氨基苯磺酸，α－萘胺显色，其吸光度与亚硝酸根离子的含量成线性关系。采用样品实测值与样品加标因收进行结果对照。回收率达到99．69％－96．86％，在定量测定的允许范围内，故该法具有可行性。     

一株好氧反硝化菌的降酚特性及反硝化关键酶活性

为了研究菌株Diaphorobacter sp.PD-7在有氧条件下降解低浓度苯酚同时反硝化的特性,采用单因素试验,摇床转速180 r/min时,最佳降酚条件为200 mg/L乙酸钠和300 mg/L苯酚同时作为碳源,培养液初始p H为7.0,温度30℃,20 h内对初始浓度300 mg/L苯酚去除率达97.3%。培养液p H为中性时,硝酸盐还原酶(NAR)与亚硝酸盐还原酶(NIR)的最适反应温度分别为35℃、40℃。用米门方程对酶促反应动力学模拟,拟合曲线与实验测定值相关性良好,参数分别为Km=0.76μmol/L、vmax=42.02×10-3U/min和Km=1.49μmol/L、vmax=32.79×10-3U/min。推测NIR可能是该菌株反硝化过程中的限速酶,菌株PD-7主要通过细胞同化作用与反硝化作用脱氮,且该菌株有着完整的反硝化途径。     

镧化合物催化酯交换合成碳酸二乙酯

以碳酸二甲酯(DMC)与乙醇进行酯交换法合成碳酸二乙酯(DEC),并考察不同催化剂、催化剂用量、反应时间、反应配比、催化剂重复性使用对反应的影响。结果表明,无水硝酸镧催化碳酸二甲酯与乙醇的酯交换反应具有优良的活性;当反应温度为76~80℃,乙醇与DMC摩尔比为8∶1,催化剂用量占DMC量的0.7%(摩尔分数)时,反应7h后DMC的转化率为86.0%,碳酸二乙酯和碳酸甲乙酯(EMC)的产率分别为59%和26.5%,酯交换反应的选择性为99.4%;催化剂无水硝酸镧在重复使用5次后仍具有很好的催化活性。     

伽马辐照对斑马鱼胚胎谷胱甘肽还原酶活性及基因表达的影响

谷胱甘肽还原酶(GR)是一种重要的抗氧化酶,其在生物体的抗氧化系统中起着关键作用.为了研究伽马辐照对斑马鱼胚胎GR活性及基因表达的影响,本实验用不同的辐照剂量(0.01、0.05、0.1、0.5和1 Gy)分别对三个发育时期(原肠胚期、体节期和咽囊期)的斑马鱼胚胎进行了辐照处理.分析了各组GR的活性,并采用荧光实时定量PCR技术(qRT-PCR)检测了GR基因的表达水平.结果显示,伽马辐照以剂量依赖的方式调整了斑马鱼胚胎GR的活性及GR基因的表达.随着辐照剂量的增加,GR活性及其mRNA的相对表达量呈现先升高后回落的趋势.这表明,GR是一种可以对伽马辐照作出早期预警的生物标志物.斑马鱼胚胎可以通过上调GR基因的表达,来增加GR的合成,从而提高对伽马射线的防御能力.但是,这种反应和调整是有限度的.咽囊期胚胎比其它两个时期的胚胎对伽马射线的防御能力更强.