Discovery and directed evolution of a glyphosate tolerance gene

The herbicide glyphosate is effectively detoxified by N-acetylation. We screened a collection of microbial isolates and discovered enzymes exhibiting glyphosate N-acetyltransferase (GAT) activity. Kinetic properties of the discovered enzymes were insufficient to confer glyphosate tolerance to transgenic organisms. Eleven iterations of DNA shuffling improved enzyme efficiency by nearly four orders of magnitude from 0.87 mM-1 min-1 to 8320 mM-1 min-1. From the fifth iteration and beyond, GAT enzymes conferred increasing glyphosate tolerance to Escherichia coli, Arabidopsis, tobacco, and maize. Glyphosate acetylation provides an alternative strategy for supporting glyphosate use on crops.     

A new strategy for the synthesis of glycoproteins

Posttranslational modifications of proteins regulate many biological processes, including metabolism, signal transduction, and gene expression. The synthetic challenges associated with generating homogeneous populations of selectively modified proteins, however, have hindered detailed studies of the effects of these modifications on protein structure and function. Here, we report an approach to the cotranslational synthesis of selectively glycosylated proteins in which the modified amino acid is genetically encoded. We show that myoglobin containing beta-N-acetylglucosamine (GlcNAc)-serine at a defined position can be expressed in Escherichia coli in good yield and with high fidelity. The beta-GlcNAc moiety can be recognized by a saccharide-binding protein, or subsequently modified with a galactosyltransferase to build more complex carbohydrates. This approach should be generally applicable to other posttranslational modifications such as protein phosphorylation, acetylation, and methylation.     

Enzymatic catalysts in organic synthesis

The synthetic value of enzymes is being increasingly recognized. With an understanding of enzyme-catalyzed reactions and the techniques now available for the low-cost production and rational alteration of enzymes and for the design of new enzymatic activities, biocatalytic synthesis should become one of the most valuable synthetic methods. The fundamental as well as the practical issues of this rapidly growing area are described and its impact on the technology pertaining to synthesis is considered.     

Evidence for reduced recombination on the nondisjoined chromosomes 21 in Down syndrome

Trisomy 21 usually results from nondisjunction during meiosis I. In order to determine whether nondisjunction results from failure of normal chromosome pairing or premature unpairing, recombination frequencies were estimated between DNA polymorphic markers on the long arm of chromosome 21 in families containing one individual with trisomy 21. The recombination frequencies on chromosomes 21 that had undergone nondisjunction were then compared to those on chromosomes 21 that had disjoined normally. The data indicate that recombination is reduced between DNA markers on nondisjoined chromosomes 21. These results are consistent with the hypothesis that reduced chiasma formation predisposes to nondisjunction, resulting in trisomy 21 in humans.     

带V型减震器的框架——核心筒体结构动力计算方法

高层框架－核心筒体结构中，在框架与核心简体连接处设置Ｖ型减震器，使框架与核心筒体之间的刚性连接变成了弹性阻尼连接，从而减小了地震作用下结构的动力反应。本文通过对带Ｖ型减震器的高度框架－核心筒体结构动力特点的分析，建立了这种减震结构的动力计算模型，提出了这种减震结构的动力计算方法，并对计算公式进行了推导。     

Cellulases Can Enhance beta-Glucan Synthesis

beta-Glucan synthesis from uridine diphosphoglucose by pea epicotyl tissue slices is increased two- to threefold by preliminary, short-term treatment with cellulases purified from auxin-treated peas. We suggest that cellulases introduce chain ends in accessible regions of cellulose microfibrils which then act as primers for chain elongation.     

塔里木地区土壤理化参数的相关性和重要性分析

随着西部油气资源的开发，大量金属设施将埋在荒漠和盐渍土中，腐蚀与腐蚀控制问题已经提到议事日程上。为此在塔北５个油区及２条长输管道沿浅近２万ｋｍ＾２的地区进行了一全面的，综合性的土壤环境腐蚀性调查，选取１０３个土壤调查点进行了测试，获得大量数据。土壤理化性质的测发为室内和野外两部分进行，并采用主分量分析法（ＰＣＡ），对测量数据中重要的２４种理化参数变量之间的关系进行了相关性及重要性分析，分析结果表明     

Selenium-containing allophycocyanin purified from selenium-enriched Spirulina platensis attenuates AAPH-induced oxidative stress in human erythrocytes through inhibition of ROS generation

Both selenium and allophycocyanin (APC) have been reported to show novel antioxidant activities. In this study, a fast protein liquid chromatographic method for purification of selenium-containing allophycocyanin (Se-APC) from selenium-enriched Spirulina platensis and the protective effect of Se-APC on 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidative stress have been described. After fractionation by ammonium sulfate precipitation, and separation by DEAE-Sepharose ion-exchange and Sephacryl S-300 size exclusion chromatography, Se-APC with purity ratio (A652/A280) of 5.30 and Se concentration of 343.02 μg g(-1) protein was obtained. Se-APC exhibited stronger antioxidant activity than APC by scavenging ABTS (2,2'-azinobis-3-ethylbenzothiazolin-6-sulfonic acid) and AAPH free radicals. The oxidative hemolysis and morphological changes induced by AAPH in human erythrocytes were effectively reversed by coincubation with Se-APC. Lipid oxidation induced by the pro-oxidant agent cupric chloride in human plasma, as evaluated by formation of conjugated diene, was blocked by Se-APC. The accumulation of malondialdehyde, loss of reduced glutathione, and increase in enzyme activities of glutathione peroxidase and reductase induced by AAPH in human erythrocytes were effectively suppressed by Se-APC. Furthermore, Se-APC significantly prevented AAPH-induced intracellular reactive oxygen species (ROS) generation. Taken together, our results suggest that Se-APC demonstrates application potential in treatment of diseases in which excess production of ROS acts as a casual or contributory factor.     

Beneficial effects of earthworms and arbuscular mycorrhizal fungi on establishment of leguminous trees on Pb/Zn mine tailings

Planting trees to stabilize metalliferous mine tailings is a widely used form of land reclamation although substantial soil amendment is invariably required, both to improve the physico-chemical status of the tailings and to ameliorate toxicity prior to planting. Here, we report a glasshouse study of the combined effects of burrowing earthworms (Pheretima guillelmi) and arbuscular mycorrhizal fungi (Glomus spp., AMF) on establishment of a naturally invasive, woody, nitrogen-fixing legume, Leucaena leucocephala, on topsoil-amended Pb/Zn mine tailings. AMF provided the most effective preliminary inoculant, improving N, P and K uptake, but earthworms had more influence improving N nutrition. In most cases, the combined effects of AMF and earthworms were additive and proved to be beneficial to plant growth, plant nutrition and for protection against uptake of toxic metals. AMF influenced metal uptake more than earthworms, but together they reduced mobility of Pb and Zn in soil by as much as 25%. Some minor but significant negative interactions were also evident; for example, earthworms enhanced soil microbial activity but inhibited the beneficial effects of AMF on N₂-fixation. We argue that increased attention to ecological interactions in soil could reduce costs and improve the efficacy of restoring a vegetation cover to land impacted by contaminated spoils.     

Effects of dredged spoils on selected microbial activities in lake column simulators

Four Lake Column Simulators were filled with hypolimnetic water from Lake Ontario and inoculated with algae and fish. Various microbial processes were monitored before and after the addition of dredged spoils. Loading rates of dredged spoils of 0.33, 3.3 or 33 g day^?1 were used for each of three columns and one column with no addition of dredged spoils was maintained as a control. The effects of dredged spoils on microbial activities were most pronounced at the highest loading rate. ³²P-PO₄ was rapidly removed from the control water but the presence of suspended particles from dredged material increased both biological assimilation and physical adsorption processes. The influence of dredged spoils on ³²P-PO₄ uptake was most pronounced immediately following loading. Dredged spoils also increased ¹⁴C-acetate mineralization in water and the effects were again more pronounced immediately following loading. A 3 fold increase in heterotrophic activity during a 1 h incubation at 20°C was observed following addition of a 33 g day^?1 loading. Dredged spoils increased the levels of N₂-fixation in the columns as indicated by the C₂H₂-reduction assay procedure. Suspended dredged material reduced light penetration and decreased primary production in the columns. The increased availability of dissolved and particulate organic and inorganic nutrients from continuous addition of dredged spoils was responsible for a general stimulation of microbial activities in the epilimnetic and hypolimnetic regions of the simulated lake columns.