高空急性缺氧的呼吸反应和P_ΛO_2数学模型

本文的目的是研究短时间高空急性缺氧呼吸反应的规律性。10名健康男性受试者,年龄18～21岁,在低压舱模拟3000～7000米高度上进行两种状态缺氧暴露:安静坐位和25瓦自行车功量计活动(VO_2=700～750ml/min;代谢率为3.3～3.6kcal/min)。在低压舱“上升”条件下P_AO_2和P_B(大气压力)呈正相关,安静状态P_AO_2=0.159×PB-17.315(r=0.999,P<0.01);25瓦活动状态P_AO_2=0.160×P_B-21.961(r=0.998,P<0.01),两者有显著的差异。随着高度上升,V_E、V_T和HR(心率)的增加均和P_AO_2呈指数型相关。可以用传递函数G(S)=K·e-τ·s/(TS 1)来描述安静和轻度活动状态下阶跃性缺氧时P_AO_2和P_B间关系。模型参数K和T存在着个体差异,同时观察到在活动状态下K值减小和T值缩短,本文对K、T值的生理意义进行了讨论。     

番茄多胺氧化酶(PAO)基因家族鉴定及表达分析

该研究通过生物信息学手段,从番茄基因组中鉴定出11个编码多胺氧化酶(polyamine oxidase,PAO)的家族基因(命名为SlPAO1~11),分为3个亚家族(Ⅰ、Ⅱ、Ⅲ);基因结构分析、蛋白质二级结构预测、亚细胞定位预测结果均显示,SlPAOs基因家族具有明显的亚家族分类特征。序列和进化分析结果显示,亚家族Ⅰ和Ⅱ中的SlPAO1~8属于典型的PAO基因,而亚家族Ⅲ中的SlPAO9~11编码蛋白还含有特异性的SWIRM结构域,SlPAO9~11属于组蛋白赖氨酸特异性脱甲基化酶,而非真正的PAO。选取上述鉴定的8个典型SlPAO基因(SlPAO1-8),采用qRT-PCR技术对SlPAO1-8基因在不同组织中(干燥种子,新鲜的真叶、子叶、茎、根)的相对表达分析显示,SlPAO1-8在不同组织中的表达水平差异显著,推测SlPAOs基因家族的组织表达多样性与功能多样性之间可能具有一定的相关性。     

The structure of a bacterial L-amino acid oxidase from Rhodococcus opacus gives new evidence for the hydride mechanism for dehydrogenation

l-Amino acid oxidase from Rhodococcus opacus (roLAAO) is classified as a member of the GR(2)-family of flavin-dependent oxidoreductases according to a highly conserved sequence motif for the cofactor binding. The monomer of the homodimeric enzyme consists of three well-defined domains: the FAD-binding domain corresponding to a general topology throughout the whole GR(2)-family; a substrate-binding domain with almost the same topology as the snake venom LAAO and a helical domain exclusively responsible for the unusual dimerisation mode of the enzyme and not found in other members of the family so far. We describe here high-resolution structures of the binary complex of protein and cofactor as well as the ternary complexes of protein, cofactor and ligands. This structures in addition to the structural knowledge of snake venom LAAO and DAAO from yeast and pig kidney permit more insight into different steps in the reaction mechanism of this class of enzymes. There is strong evidence for hydride transfer as the mechanism of dehydrogenation. This mechanism appears to be uncommon in a sense that the chemical transformation can proceed efficiently without the involvement of amino acid functional groups. Most groups present at the active site are involved in substrate recognition, binding and fixation, i.e. they direct the trajectory of the interacting orbitals. In this mode of catalysis orbital steering/interactions are the predominant factors for the chemical step(s). A mirror-symmetrical relationship between the two substrate-binding sites of d and l-amino acid oxidases is observed which facilitates enantiomeric selectivity while preserving a common arrangement of the residues in the active site. These results are of general relevance for the mechanism of flavoproteins and lead to the proposal of a common dehydrogenation step in the mechanism for l and d-amino acid oxidases.     

The chlorophyllases AtCLH1 and AtCLH2 are not essential for senescence-related chlorophyll breakdown in Arabidopsis thaliana

One important reaction of chlorophyll (chl) breakdown during plant senescence is the removal of the lipophilic phytol moiety by chlorophyllase. AtCLH1 and AtCLH2 were considered to be required for this reaction in Arabidopsis thaliana. Here we present evidence against this assumption. Using green fluorescent protein fusions, neither AtCLH isoform localizes to chloroplasts, the predicted site of chlorophyll breakdown. Furthermore, clh1 and clh2 single and double knockout lines are still able to degrade chlorophyll during senescence. From our data we conclude that AtCLHs are not required for senescence-related chlorophyll breakdown in vivo and propose that genuine chlorophyllase has not yet been molecularly identified.     

Short-term temperature effects on the anaerobic metabolism of glycogen accumulating organisms

Proliferation of glycogen accumulating organisms (GAO) has been identified as a potential cause of enhanced biological phosphorus removal (EBPR) failure in wastewater treatment plants (WWTP). GAO compete for substrate with polyphosphate accumulating organisms (PAO) that are the microorganisms responsible for the phosphorus removal process. In the present article, the effects of temperature on the anaerobic metabolism of GAO were studied in a broad temperature range (from 10 to 40 degrees C). Additionally, maximum acetate uptake rate of PAO, between 20 and 40 degrees C, was also evaluated. It was found that GAO had clear advantages over PAO for substrate uptake at temperatures higher than 20 degrees C. Below 20 degrees C, maximum acetate uptake rates of both microorganisms were similar. However, lower maintenance requirements at temperature lower than 30 degrees C give PAO metabolic advantages in the PAO-GAO competition. Consequently, PAO could be considered to be psychrophilic microorganisms while GAO appear to be mesophilic. These findings contribute to understand the observed stability of the EBPR process in WWTP operated under cold weather conditions. They may also explain the proliferation of GAO in WWTP and thus, EBPR instability, observed in hot climate regions or when treating warm industrial effluents. It is suggested to take into account the observed temperature dependencies of PAO and GAO in order to extend the applicability of current activated sludge models to a wider temperature range.     

胶质芽孢杆菌HM8841紫外线诱变育种研究

以胶质芽孢杆菌HM8841作为出发菌株,通过紫外线诱变和突变菌株性能测定,选育出3株适合生产发酵的优良菌种。与出发菌株相比,突变株具有缩短发酵周期,提高发酵水平,增强芽孢抗逆性能等特点。     

Versatility of peroxisomes: An evolving concept

Research spanning almost 50 years has highlighted unique characteristics and irreplaceable list of diverse functions performed by peroxisomes in various model systems. Peroxisomes are single membrane bound highly dynamic organelles ubiquitous to most eukaryotic cells. Proliferation by division of pre-existing organelles and the role of endoplasmic reticulum in the biogenesis of these organelles is now well established. The earliest identified conserved functions of peroxisomes are β-oxidation of fatty acids and reactive oxygen species metabolism. Several studies over the last few decades have reported the importance of this organelle and its numerous cell type, tissue and environment-dependent functions. Their role in several aspects of human health and disease is now under investigation. Studies related to peroxisome biology and functions are now also extended to diverse model systems like Drosophila melanogaster, trypanosomatids, etc. Peroxisomes also intricately collaborate and carry out these functions together with several other organelles in a cell. In this review, we aim to present an overview of our current knowledge of the repertoire of functions of peroxisomes in various model systems.     

A benzimidazole-based ruthenium(IV) complex inhibits Pseudomonas aeruginosa biofilm formation by interacting with siderophores and the cell envelope,and inducing oxidative stress

Pseudomonas aeruginosa biofilm-associated infections are a serious medical problem, and new compounds and therapies acting through novel mechanisms are much needed. Herein, the authors report a ruthenium(IV) complex that reduces P. aeruginosa PAO1 biofilm formation by 84%, and alters biofilm morphology and the living-to-dead cell ratio at 1?mM concentration. Including the compound in the culture medium altered the pigments secreted by PAO1, and fluorescence spectra revealed a decrease in pyoverdine. Scanning electron microscopy showed that the ruthenium complex did not penetrate the bacterial cell wall, but accumulated on external cell structures. Fluorescence quenching experiments indicated strong binding of the ruthenium complex to both plasmid DNA and bovine serum albumin. Formamidopyrimidine DNA N-glycosylase (Fpg) protein digestion of plasmid DNA isolated after ruthenium(IV) complex treatment revealed the generation of oxidative stress, which was further proved by the observed upregulation of catalase and superoxide dismutase gene expression.     

Nonlinear modelisation of heavy metal removal from aqueous solution using Ulva lactuca algae

After extensive analysis, Ulva lactuca dried algae, collected from the Monastir coastal zone, was proven to be successful as an adsorbent for the removal of certain inorganic pollutants. The main objective of this study was the nonlinear modeling of heavy metal removal from an aqueous solution, using a freely available and well analyzed biomaterial, as well as the evaluation of its efficacy on various metal ion sorptions. Although relatively low specific surface area, compared to more conventional adsorbents, the selected biomaterial displays very interesting retention capacities when used with aqueous inorganic pollutants. The pseudo, first and second-order kinetic models were used to investigate the kinetic retention mechanism. Assuming the nonlinear form, the results indicate that the retention mechanism is diffusion controlled. Concerning the heavy metal uptake capacity, it was found that the selected biomaterial has a retention capacity of 67 mg g⁻¹ of Ni(II), 112 mg g⁻¹ of Cu(II), 127 mg g⁻¹of Cd(II) and 230 mg g⁻¹ of Pb(II).     

Relative contributions of archaea and bacteria to microbial ammonia oxidation differ under different conditions during agricultural waste composting

The aim of this study was to compare the relative contribution of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to nitrification during agricultural waste composting. The AOA and AOB amoA gene abundance and composition were determined by quantitative PCR and denaturing gradient gel electrophoresis (DGGE), respectively. The results showed that the archaeal amoA gene was abundant throughout the composting process, while the bacterial amoA gene abundance decreased to undetectable level during the thermophilic and cooling stages. DGGE showed more diverse archaeal amoA gene composition when the potential ammonia oxidation (PAO) rate reached peak values. A significant positive relationship was observed between the PAO rate and the archaeal amoA gene abundance (R2=0.554; P<0.001), indicating that archaea dominated ammonia oxidation during the thermophilic and cooling stages. Bacteria were also related to ammonia oxidation activity (R2=0.503; P=0.03) especially during the mesophilic and maturation stages.