External Na dependence of ouabain-sensitive ATP:ADP exchange initiated by photolysis of intracellular caged-ATP in human red cell ghosts

Coupled active transport of Na+ and K+ across cellular plasma membranes is mediated by (Na+ + K+)-stimulated Mg2+-dependent ATPase. Active cation transport by this Na pump involves a cyclic Na-dependent phosphorylation of the enzyme by intracellular ATP and hydrolytic dephosphorylation of the phosphoenzyme, stimulated by K+ (ref. 1). In human red blood cells, skeletal muscle and squid axons, replacement of extracellular K by Na results in a ouabain-sensitive efflux of Na coupled to an influx of extracellular Na. There is apparently no net Na movement nor net hydrolysis of ATP. The rate of Na:Na exchange is stimulated by increased levels of ADP and exchange transport is not observed in cells totally depleted of intracellular ATP. These characteristics suggest that the biochemical mechanism underlying the Na exchange mode of the Na pump involves phosphorylation of the enzyme by ATP (which requires intracellular Na) followed by its dephosphorylation by ADP. Such a reaction has been observed in partially purified (Na+ + K+) ATPase from a variety of sources and its dependence on Na concentration has been described (although not previously for the red cell enzyme). In the present work, intracellular ATP:ADP exchange reaction was initiated by photoreleased ATP following brief irradiation at 350 nm of ghosts containing caged-ATP. The ouabain-sensitive component of the ensuing ATP:ADP exchange reaction shows a biphasic response to extracellular Na. External Na in the range 0--10 mM has an inhibitory effect whilst increasing concentrations beyond this range stimulate the rate of exchange in a roughly linear fashion up to 100 mM Na. These results represent the first direct demonstration of the sidedness of the effects of Na on this partial sequence in the overall enzyme cycle and bear a qualitative resemblance to the Na effects on the Na-ATPase which occur in the absence of intracellular ADP in human red blood cells.     

H-A-O工艺强化脱氮及系统内污泥减量的研究

为提高生活污水传统处理工艺反硝化脱氮能力并在系统内部实现污泥减量,设计水解酸化-缺氧-好氧(H-A-O)生物脱氮及污泥减量组合工艺。试验采用连续运行方式,以实际生活污水为对象,进水化学需氧量(COD)为220～410 mg/L,进水NH4+-N质量浓度为36～58 mg/L,硝化液回流比(r)为300％。试验结果表明：水解酸化作用使原水的可生化性提高60％;系统在无外加碳源和碱度条件下,COD,NH14+-N和TN的去除率分别达到90％,95％和74％,其中总氮(TN)去除效果提高12％;当以污泥水解酸化出水和生活污水作为反硝化碳源时,最大NO3--N反硝化速率分别为0.75 mg/min和0.66 mg/min;H-A-O系统利用水解酸化作用实现剩余污泥减量为37％,同时提高系统的脱氮效果。     

Structure of mammalian AMPK and its regulation by ADP

The heterotrimeric AMP-activated protein kinase (AMPK) has a key role in regulating cellular energy metabolism; in response to a fall in intracellular ATP levels it activates energy-producing pathways and inhibits energy-consuming processes. AMPK has been implicated in a number of diseases related to energy metabolism including type 2 diabetes, obesity and, most recently, cancer. AMPK is converted from an inactive form to a catalytically competent form by phosphorylation of the activation loop within the kinase domain: AMP binding to the γ-regulatory domain promotes phosphorylation by the upstream kinase, protects the enzyme against dephosphorylation, as well as causing allosteric activation. Here we show that ADP binding to just one of the two exchangeable AXP (AMP/ADP/ATP) binding sites on the regulatory domain protects the enzyme from dephosphorylation, although it does not lead to allosteric activation. Our studies show that active mammalian AMPK displays significantly tighter binding to ADP than to Mg-ATP, explaining how the enzyme is regulated under physiological conditions where the concentration of Mg-ATP is higher than that of ADP and much higher than that of AMP. We have determined the crystal structure of an active AMPK complex. The structure shows how the activation loop of the kinase domain is stabilized by the regulatory domain and how the kinase linker region interacts with the regulatory nucleotide-binding site that mediates protection against dephosphorylation. From our biochemical and structural data we develop a model for how the energy status of a cell regulates AMPK activity.     

细胞外ATP调节了NaCl胁迫诱导的烟草悬浮细胞的死亡和呼吸的抑制

本文以烟草悬浮细胞BY-2为材料,探讨了胞外ATP对NaCl诱导的细胞死亡和呼吸抑制的调节作用。实验表明,随着NaCl浓度的逐渐上升(50、100、200、400 mmol/L),细胞的死亡水平逐渐上升,而胞外ATP含量和细胞呼吸速率则随NaCl浓度的上升而逐渐下降。本文在200 mmol/L NaCl处理下的细胞中探索了胞外ATP对NaCl诱导的细胞死亡和呼吸抑制的调节作用。结果发现,较之200 mmol/L NaCl胁迫下的细胞,对NaCl胁迫的细胞加入外源ATP(20 μmol/L )其使得细胞死亡水平显著性降低,也使得胞外ATP含量和细胞呼吸速率均有所回升。上述实验观察表明,NaCl胁迫诱导的植物细胞的死亡和呼吸抑制可能和细胞外ATP水平的变化有关,而胞外ATP对NaCl诱导的细胞死亡具有一定的调节作用。     

化学磷回收促进脱氮除磷和污泥减量的实验研究

文章采用改进A2O工艺(辅助化学磷回收)进行脱氮除磷和污泥减量的实验研究。实验结果表明,在进水COD质量浓度为150~180 mg/L时,COD、氨氮和总磷的去除率分别达到90%、97.9%、91.6%,结合化学磷回收后污泥产量减少约为10%~25%,并可进行磷的回收,实现磷的可持续发展,大大提高了污水处理厂的运行效益。     

碳热还原氮化一步法制备钒氮合金工艺研究

对V2O5自还原氮化过程进行热力学分析,并以工业级V2O5和炭黑为原料,经过混料、研磨、压制成块后进行烧结和还原氮化,制得含氮量较高的钒氮合金。结果表明,为了避免V2O5在还原过程中挥发,预还原温度应控制在V2O5熔点(678℃)以下;经过650℃预还原4h,试样中的V2O5才能全部转化为低价态的钒氧化物;V2O5在N2气氛下自还原时,还原终温低于1 271℃时,还原产物优先生成VN,还原终温高于1 271℃时,还原产物中才会出现大量VC;为保证还原产物的高氮和低碳含量,应将还原氮化最终温度控制在1 200～1 300℃。     

活性炭纤维表面含氧基团及其对NO的还原

利用程序升温还原装置（ＴＰＲ）和程序升温脱附（ＴＰＤ）、热重（ＴＧ）等试验方法,证明了未改性、硝酸基、铜基的活性炭纤维（ＡＣＦ）上均存在含氧基团。在躲开反应器中对这些ＡＣＦ与ＮＯ的反应产物进行了定量测定,发现ＮＯ脱除率与ＡＣＦ含氧量和表面含氧基团的存在及分布有关。还考察了ＣＯ的存在对该反应的影响。     

油页岩CS2-NMP萃取物中含氮化合物的分离与分析

为分离油页岩萃取物的含氮化合物,采用索氏萃取法,以CS2-NMP为萃取剂,在60℃条件下萃取依兰油页岩。采用中性氧化铝色谱柱对萃取物进行分离,并对含氮洗脱成分进行GC/MS分析。结果表明：中性氧化铝色谱法能实现萃取物的初步分离,分离获得的含氮化合物组分的质量分数不大于1.8%;萃取物所含的22种氮化合物有21种杂环化合物。这些含氮化合物为喹啉、吡啶、吲哚、酰胺等的衍生物。该结果为依兰油页岩的成因及油母结构研究提供了参考。     

Generation process of FeS and its inhibition mechanism on iron mineral reduction in selective direct reduction of laterite nickel ore

Numerous studies have demonstrated that Na₂SO₄ can significantly inhibit the reduction of iron oxide in the selective reduction process of laterite nickel ore. FeS generated in the process plays an important role in selective reduction, but the generation process of FeS and its inhibition mechanism on iron reduction are not clear. To figure this out, X-ray diffraction and scanning electron microscopy analyses were conducted to study the roasted ore. The results show that when Na₂SO₄ is added in the roasting, the FeO content in the roasted ore increases accompanied by the emergence of FeS phase. Further analysis indicates that Na₂S formed by the reaction of Na₂SO₄ with CO reacts with SiO₂ at the FeO surface to generate FeS and Na₂Si₂O₅. As a result, a thin film forms on the surface of FeO, hindering the contact between reducing gas and FeO. Therefore, the reduction of iron is depressed, and the FeO content in the roasted ore increases.     

乙炔法气相合成醋酸乙烯催化剂的研究综述

从乙炔法气相合成醋酸乙烯的反应机理入手,综述了醋酸锌/活性炭催化剂的载体、活性组分、助剂以及失活机理的国内外研究情况.     

Green chemistry: C-C coupling and asymmetric reduction by innovative catalysis

A catalytic method has been developed, which allows aryl halides to couple with various electron-rich olefins to give 1,1’-substituted olefins. The palladium-catalysed coupling in ionic liquid solvent proceeds with high efficiency and remarkable regioselectivity without the need for any costly or toxic halide scavengers. Parallel to this, an environmentally-appealing method for the asymmetric reduction of ketones has been established, with which a variety of chiral alcohols can be accessed with high enantioselectivity in water with no need for any organic solvents. The same chemistry has been explored for the reduction of aldehydes, which is shown to be fast and highly chemoselective. These methods add new tools to the armoury of synthetic chemists.     

Green chemistry: C-C coupling and asymmetric reduction by innovative catalysis

A catalytic method has been developed, which allows aryl halides to couple with various electron-rich olefins to give 1,1＇-substituted olefins. The palladium-catalysed coupling in ionic liquid solvent proceeds with high efficiency and remarkable regioselectivity without the need for any costly or toxic halide scavengers. Parallel to this, an environmentally-appealing method for the asymmetric reduction of ketones has been established, with which a variety of chiral alcohols can be accessed with high enantioselectivity in water with no need for any organic solvents. The same chemistry has been explored for the reduction of aldehydes, which is shown to be fast and highly chemoselective. These methods add new tools to the armoury of synthetic chemists.