Microbial detoxification of superoxide: the non-heme iron reductive paradigm for combating oxidative stress

A reductive paradigm has emerged in recent years for detoxification of superoxide and other redox active diatomic molecules in air-sensitive bacteria and archaea. Adventitiously generated superoxide in many anaerobic or microaerophilic bacteria and archaea is scavenged by superoxide reductase (SOR) rather than the classical superoxide dismutases characteristic of aerobic microbes. SORs contain a novel five-coordinate, square-pyramidal [Fe(His)4(Cys)] ferrous active site, which adds a sixth glutamate ligand upon oxidation. This Account summarizes the recently elucidated structural and mechanistic features of SORs. The non-heme iron reductive scavenging paradigm in these air-sensitive microbes also extends to recently characterized enzymes that scavenge hydrogen peroxide and nitric oxide and to oxygen sensing proteins.     

Finding intermediates in the O2 activation pathways of non-heme iron oxygenases

Intermediates in the reaction cycle of an oxygenase are usually very informative with respect to the chemical mechanism of O 2 activation and insertion. However, detection of these intermediates is often complicated by their short lifetime and the regulatory mechanism of the enzyme designed to ensure specificity. Here, the methods used to detect the intermediates in an extradiol dioxygenase, a Rieske cis-dihydrodiol dioxygenase, and soluble methane monooxygenase are discussed. The methods include the use of alternative, chromophoric substrates, mutagenesis of active site catalytic residues, forced changes in substrate binding order, control of reaction rates using regulatory proteins, and initialization of catalysis in crystallo.     

Rapid purification of rabbit reticulocyte lipoxygenase for electron paramagnetic spectroscopy characterization of the non-heme iron

An efficient three-step purification technique has been developed for the reticulocyte 15-lipoxygenase from rabbit. Ammonium sulfate fractionated reticulocyte lysate was purified by size exclusion chromatography and preparative scale isoelectric focusing. The entire procedure was complete in less than eight hours and was carried out in batches which typically yielded 10 mg of purified enzyme. The identity and purity of the enzyme were evaluated byN-terminal sequencing, sodium dodecylsulfate polyacrylamide gel electrophoresis and specific activity determinations. The enzyme contained approximately one g-atom iron per mole of protein. The iron was present in an electron paramagnetic spectroscopy (EPR) silent, presumably high spin iron(II), form in the isolated enzyme. Treatment with one equivalent of 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid resulted in the appearance of an EPR signal around g6.     

Understanding the effects of sulfur on mercury capture from coal-fired utility flue gases

Coal combustion continues to be a major source of energy throughout the world and is the leading contributor to anthropogenic mercury emissions. Effective control of these emissions requires a good understanding of how other flue gas constituents such as sulfur dioxide (SO₂) and sulfur trioxide (SO₃) may interfere in the removal process. Most of the current literature suggests that SO₂ hinders elemental mercury (Hg⁰) oxidation by scavenging oxidizing species such as chlorine (Cl₂) and reduces the overall efficiency of mercury capture, while there is evidence to suggest that SO₂ with oxygen (O₂) enhances Hg⁰ oxidation by promoting Cl₂ formation below 100 °C. However, studies in which SO₂ was shown to have a positive correlation with Hg⁰ oxidation in full-scale utilities indicate that these interactions may be heavily dependent on operating conditions, particularly chlorine content of the coal and temperature. While bench-scale studies explicitly targeting SO₃ are scarce, the general consensus among full-scale coal-fired utilities is that its presence in flue gas has a strong negative correlation with mercury capture efficiency. The exact reason behind this observed correlation is not completely clear, however. While SO₃ is an inevitable product of SO₂ oxidation by O₂, a reaction that hinders Hg⁰ oxidation, it readily reacts with water vapor, forms sulfuric acid (H₂SO₄) at the surface of carbon, and physically blocks active sites of carbon. On the other hand, H₂SO₄ on carbon surfaces may increase mercury capacity either through the creation of oxidation sites on the carbon surface or through a direct reaction of mercury with the acid. However, neither of these beneficial impacts is expected to be of practical significance for an activated carbon injection system in a real coal-fired utility flue gas.     

Production of the enzyme dihydrofolate reductase by methotrexate-resistant bacteria isolated from soil

Six bacterial cultures isolated from soil were capable of growing in the presence of methotrexate (MTX). Two strains, PFR-1 and 3, developed resistance to 500 μg cm^?3 MTX in the medium and produced elevated levels of the enzyme dihydrofolate reductase (EC 1.5.1.3): 2580 and 2702 U dm^?3 compared to the sensitive parent strains (28 and 35 U dm^?3). Isolate PFR-3 showed maximum enzyme production (4950 U dm^?3, specific activity 12.56 U mg^?1 in flasks and 5737 U dm^?3, specific activity 14.80 U mg^?1 in 5-dm³ fermenter) during exponential phase of growth (6 h) at 37°C and pH 7.0.     

The structure of iron superoxide dismutase from Pseudomonas ovalis complexed with the inhibitor azide

The 2.9 Å resolution structure of iron superoxide dismutase(FeSOD) (EC 1.15.1.1 [EC] ) from Pseudomonas ovalis complexed withthe inhibitor azide was solved. Comparison of this structurewith free enzyme shows that the inhibitor is bound at the opencoordination position of the iron, with a bond length of 2.0Å. The metal moves by 0.4 Å into the trigonal planeto produce an orthogonal geometry at the iron. Binding of theinhibitor also causes a movement of the axial ligand (histidine26) away from the metal, a lengthening of the iron—histidinebond, and a rotation of the histidine 74 ring. The inhibitorpossesses contacts in the binding pocket with a pair of conservedtryptophan residues and with the side chains of tyrosine 34and glutamine 70. This glutamine is conserved between all FeSODs,but is absent in MnSOD. Comparisons with MnSOD show that a differentglutamine which possesses the same interactions in the activesite as Gln70 in FeSOD is conserved at position 154 in the overallSOD sequence, implying that while manganese and FeSODs are structuralhomologues in a global sense, their functional and evolutionaryrelationship is that of second-site mutation revertants.     

Binding energetics of ferredoxin-NADP+ reductase with ferredoxin and its relation to function

To obtain insight into the motional features of proteins for enzymatic function, we studied binding reactions between ferredoxin-NADP(+) reductase (FNR) and ferredoxin (Fd) using isothermal titration calorimetry and NMR-based magnetic relaxation and hydrogen/deuterium exchange (HD(ex)). Fd-FNR binding was accompanied by endothermic reactions and driven by the entropy gain. Component-wise analysis of the net entropy change revealed that increases in the conformational entropy of the Fd-FNR complex contributed largely to stabilizing the complex. Intriguingly, analyses of magnetic relaxation and HD(ex) rates with X-ray B factor implied that Fd binding led to both structural stiffening and softening of FNR. Enhanced FNR backbone fluctuations suggest favorable contributions to the net conformational entropy. Fd-bound FNR further showed that relatively large-scale motions of the C terminus, a gatekeeper for interactions of NADP(+) (H), were quenched in the closed form, thereby facilitating exit of NADP(+) (H). This can provide a first dynamic structure-based explanation for the negative cooperativity between Fd and NADP(+) (H) via FNR.     

世博遗产中巴斯夫的身影

中国,上海（2010年11月11日）2010年堪称历史上最成功的上海世博会已经落下帷幕,但一系列项目、设计和活动仍将继续展现巴斯夫如何创造化学新作用,为中国以及全世界的城市、家庭以及下一代带来积极作用。在2010年上海世博会上,巴斯夫针对全球各地的城市所面临的共同挑战,提供了各种创新的解决方案,力求寻找使城市化与可持续性发展和谐共存的双赢方案。     

Oxidation of hydrogen sulfide to elementary sulfur on an activated carbon bed in the presence of iron (III) chloride aerosol

Oxidation of H₂S to elemental sulfur in a gas stream at room temperature was examined in a bed of activated carbon. The reaction was observed in the presence and absence of a ferric chloride aerosol.The H₂S concentration was in the range 500 – 2000 p.p.m., gas velocities from 4.2 – 22.5 cm/sec and aerosol concentration in the range 0.001 – 1 mg/l air.The activity of carbon as an adsorbent catalyst dropped to a relatively low value within a short time in the absence of the aerosol. The ferric chloride aerosol, which acted as another catalyst, improved the removal of H₂S to a great extent. This improvement depended on the concentration of the aerosol. Up to 98% removal was obtainable and was maintained indefinitely. These results suggest that iron chloride aerosols may be used to remove H₂S from gas streams in a dry particle bed of adsorptive material.     

Catalytic effects of iron compounds and the role of sulfur in coal liquefaction and hydrogenolysis of SRC

Effective iron catalysts in coal liquefaction have been explored. Reduced Fe, Fe(CO)₅, and ferrocene have shown a considerably high catalytic activity in the liquefaction of Yallourn coal at 400°C. Degree of reduction has been shown to be one of the most important factors determining the catalytic activity of the iron catalyst. In the hydrogenolysis of SRC derived from Wandoan coal, water formed in situ has been shown to exhibit a negative effect due to reoxidation of the iron catalyst, but addition of elemental sulfur is greatly effective in preventing such deleterious influence of water. This can be interpreted on the basis of the sulfidation of reduced Fe by elemental sulfur, competing with reoxidation of the iron catalyst by water. In the systems with elemental sulfur, active and oxidation-proof pyrrhotite is formed, and the degree of reduction of the remaining iron oxide is maintained higher than that in the absence of elemental sulfur.     

UF technology contributes to the recycling of dye salt solutions

Working in conjunction with an Indian textile manufacturer situated in the state of Tamil Nadu, the membrane filtration specialist Hydranautics has devised a new system that enables the recycling of the salt solution used in its dyes. The system was successfully tested in July of this year and is now in full operation at the processing plant, where it is helping to cut costs and save unnecessary waste. Hydranautics' role in the project involved designing an ultrafiltration (UF) system for the recycling process. The company selected its HYDRAcap® capillary membranes for the duty, which offers particulate removal down to 0.1 microns in size.     

浅谈如何提高PVC树脂质量

分析了PVC树脂的质量指标,围绕杂质粒子数、挥发物含量、残留VCM含量等7项质量指标超标问题,提出了一系列措施,该措施实施后提高了PVC树脂的质量。     

Specifically immobilised aldo/keto reductase AKR1A1 shows a dramatic increase in activity relative to the randomly immobilised enzyme

The difference between site-specific and random immobilisation of the aldo/keto reductase AKR1A1 was explored. AKR1A1 was recombinantly expressed as a thioester by the intein strategy. The thioester was selectively modified with a biotin label by the expressed protein ligation method, and subsequent immobilisation on streptavidin templates was performed. Adsorption of wild-type AKR1A1 to streptavidin templates and of biotinylated AKR1A1 to uncoated templates was used to study randomly immobilised enzymes. Investigation of the kinetic parameters revealed remarkably improved activity for the site-specifically immobilised enzyme, which was comparable to that of the wild-type enzyme in solution and 60-300-fold greater than that of the randomly immobilized enzymes. Furthermore, the enzyme was surprisingly stable. No loss of activity was observed for over a week, and even after 50 days more than 35% of activity was maintained.     

Use of compacts to study the mechanical properties of sulfur

Modulus of elasticity and microhardness measurements were made on compacts of four sulfur preparations having different crystallinities morphologies and a wide range of porosities. Compacts amde from Crystex — a high polymeric sulfur — had mechanical properties inferior to those of other preparations studied. Annealing compacts resulted in a large increase in microhardness. Measurements of modulus of elasticity and microhardness of sulfur compacts reinforced with poly (ethylene terephthalate) fibers were made for a wide range of porosities.     

Electrochemical reduction of carbon dioxide and the effect of the enzyme carbonic anhydrase 11 on iron corrosion

The corrosion of pure iron in carbon dioxide saturated solutions at low temperatures has been investigated in this study. Both dc polarisation and ac impedance techniques were used in conjunction with a rotating disc electrode to investigate the reaction sequence leading to hydrogen evolution at 30°C. The results indicate that protons from the low pH solution, the bicarbonate ion and the undissociated carbonic acid molecule contribute to the reaction sequence leading to eventual hydrogen evolution. The corrosion mechanism involves both activation and diffusion processes. A rotating disc electrode in combination with ac techniques and the enzyme carbonic anhydrate II, EC 4.2.1.1, were used to characterise the diffusion effects. A chemical–electrochemical cathodic reaction mechanism is proposed.     

提高克劳斯硫回收装置收率的方法

基于某厂克劳斯硫回收装置,对影响克劳斯硫回收率的因素进行分析,发现反应温度、酸气组成、催化剂、工艺及设备等因素对硫回收率产生重要影响;提出了改进措施来提高克劳斯硫回收装置的回收率,包括:①使用主、副调节阀减小酸性气流量变化的影响;②应用在线分析仪,控制反应计量比;③采用预热空气和酸性气等方法处理含NH3酸性气;④选用性能好的催化剂;⑤调节高温掺合阀开度,控制一级转化器操作温度;⑥采用过程气换热器加热,通过旁路来控制二级转化器操作温度。     

Kinetic studies on the reactions involved in the hot gas desulfurization using a regenerable iron oxide sorbent—II: Reactions of iron sulfide with oxygen and sulfur dioxide

In the hot gas desulfurization process using iron oxide sorbent, the regeneration of the sulfided iron oxide sorbent consists of two reactions: the oxidation of iron sulfide with air, and its reaction with the sulfur dioxide formed during the air oxidation. This part describes the kinetic studies on the reactions of iron sulfide (formed by the reactions of Fe₂O₃ with H₂CO mixture and subsequendy with H₂S) with oxygen and sulfur dioxide. The experimental and analysis procedures used are similar to those outlined in Part I of this paper.The activation energies for the oxygen and the sulfur dioxide reactions are found to be 15.63 and 17.5 kcal/mol, respectively. Notably, the product oxides formed in the two cases are different. With air, the reaction is fast and the final product is Fe₂O₃, whereas with SO₂, the major product is Fe₃O₄, which slowly oxidizes to Fe₂O₃ in a secondary step. Also, in the latter reaction elemental sulfur is formed.     

浅谈如何减少泵泄漏

随着人们环保意识的日益增强和环保法规的逐步健全,泵泄漏的问题越来越引起人们的重视。着重阐述了减少泵泄漏的两条途径,一是改善有密封泵的轴封装置;二是采用无密封泵。