Premicellar complexes of sphingomyelinase mediate enzyme exchange for the stationary phase turnover

During the steady state reaction progress in the scooting mode with highly processive turnover, Bacillus cereus sphingomyelinase (SMase) remains tightly bound to sphingomyelin (SM) vesicles (Yu et al., Biochim. Biophys. Acta 1583, 121-131, 2002). In this paper, we analyze the kinetics of SMase-catalyzed hydrolysis of SM dispersed in diheptanoylphosphatidyl-choline (DC₇PC) micelles. Results show that the resulting decrease in the turnover processivity induces the stationary phase in the reaction progress. The exchange of the bound enzyme (E*) between the vesicle during such reaction progress is mediated via the premicellar complexes (E_i^#) of SMase with DC₇PC. Biophysical studies indicate that in E_i^# monodisperse DC₇PC is bound to the interface binding surface (i-face) of SMase that is also involved in its binding to micelles or vesicles. In the presence of magnesium, required for the catalytic turnover, three different complexes of SMase with monodisperse DC₇PC (E_i^# with i = 1, 2, 3) are sequentially formed with Hill coefficients of 3, 4 and 8, respectively. As a result, during the stationary phase reaction progress, the initial rate is linear for an extended period and all the substrate in the reaction mixture is hydrolyzed at the end of the reaction progress. At low mole fraction (X) of total added SM, exchange is rapid and the processive turnover is limited by the steps of the interfacial turnover cycle without becoming microscopically limited by local substrate depletion or enzyme exchange. At high X, less DC₇PC will be monodisperse, E_i^# does not form and the turnover becomes limited by slow enzyme exchange. Transferred NOESY enhancement results show that monomeric DC₇PC in solution is in a rapid exchange with that bound to E_i^# at a rate comparable to that in micelles. Significance of the exchange and equilibrium properties of the E_i^# complexes for the interpretation of the stationary phase reaction progress is discussed.     

Evaluating the efficacy of planktonic foraminifer calcite δO data for sea surface temperature reconstruction for the Late Miocene

This study examines the efficacy of published δ¹⁸O data from the calcite of Late Miocene surface dwelling planktonic foraminifer shells, for sea surface temperature estimates for the pre-Quaternary. The data are from 33 Late Miocene (Messinian) marine sites from a modern latitudinal gradient of 64°N to 48°S. They give estimates of SSTs in the tropics/subtropics (to 30°N and S) that are mostly cooler than present. Possible causes of this temperature discrepancy are ecological factors (e.g. calcification of shells at levels below the ocean mixed layer), taphonomic effects (e.g. diagenesis or dissolution), inaccurate estimation of Late Miocene seawater oxygen isotope composition, or a real Late Miocene cool climate. The scale of apparent cooling in the tropics suggests that the SST signal of the foraminifer calcite has been reset, at least in part, by early diagenetic calcite with higher δ¹⁸O, formed in the foraminifer shells in cool sea bottom pore waters, probably coupled with the effects of calcite formed below the mixed layer during the life of the foraminifera. This hypothesis is supported by the markedly cooler SST estimates from low latitudes—in some cases more than 9 °C cooler than present—where the gradients of temperature and the δ¹⁸O composition of seawater between sea surface and sea bottom are most marked, and where ocean surface stratification is high. At higher latitudes, particularly N and S of 30°, the temperature signal is still cooler, though maximum temperature estimates overlap with modern SSTs N and S of 40°. Comparison of SST estimates for the Late Miocene from alkenone unsaturation analysis from the eastern tropical Atlantic at Ocean Drilling Program (ODP) Site 958—which suggest a warmer sea surface by 2-4 °C, with estimates from oxygen isotopes at Deep Sea Drilling Project (DSDP) Site 366 and ODP Site 959, indicating cooler than present SSTs, also suggest a significant impact on the δ¹⁸O signal. Nevertheless, much of the original SST variation is clearly preserved in the primary calcite formed in the mixed layer, and records secular and temporal oceanographic changes at the sea surface, such as movement of the Antarctic Polar Front in the Southern Ocean. Cooler SSTs in the tropics and sub-tropics are also consistent with the Late Miocene latitude reduction in the coral reef belt and with interrupted reef growth on the Queensland Plateau of eastern Australia, though it is not possible to quantify absolute SSTs with the existing oxygen isotope data. Reconstruction of an accurate global SST dataset for Neogene time-slices from the existing published DSDP/ODP isotope data, for use in general circulation models, may require a detailed re-assessment of taphonomy at many sites.     

大肠癌发病地理特征的趋势面分析

了解嘉善县大肠癌发病的地理分布特征及地理趋势,为研究大肠癌的病因提供一些线索,嘉善县大肠癌发病率有地域差异,应进一步研究各地区地理环境、生活习惯、经济状况等因素的差异及其与大肠癌的关系,对于存在异常残差值的地区,应作为重点研究对象。探讨这些地区可能存在的某种保护或危险因素。     

Managing vegetation in surface-flow wastewater-treatment wetlands for optimal treatment performance

Constructed wetlands that mimic natural marshes have been used as low-cost alternatives to conventional secondary or tertiary wastewater treatment in the U.S. for at least 30 years. However, the general level of understanding of internal treatment processes and their relation to vegetation and habitat quality has not grown in proportion to the popularity of these systems. We have studied internal processes in surface-flow constructed wastewater-treatment wetlands throughout the southwestern U.S. since 1990. At any given time, the water quality, hydraulics, water temperature, soil chemistry, available oxygen, microbial communities, macroinvertebrates, and vegetation each greatly affect the treatment capabilities of the wetland. Inside the wetland, each of these components plays a functional role and the treatment outcome depends upon how the various components interact. Vegetation plays a uniquely important role in water treatment due to the large number of functions it supports, particularly with regard to nitrogen transformations. However, it has been our experience that vegetation management is critical for achieving and sustaining optimal treatment function. Effective water treatment function and good wildlife quality within a surface-flow constructed wetland depend upon the health and sustainability of the vegetation. We suggest that an effective tool to manage and sustain healthy vegetation is the use of hummocks, which are shallow emergent plant beds within the wetland, positioned perpendicular to the water flow path and surrounded by water sufficiently deep to limit further emergent vegetation expansion. In this paper, we describe the use of a hummock configuration, in conjunction with seasonal water level fluctuations, to manage the vegetation and maintain the treatment function of wastewater-treatment wetlands on a sustainable basis.     

不同固定条件下细胞与活细胞的原子力显微镜实时观察

用原子力显微镜（atom force microscope,AFM）观察固定细胞的最佳条件并在生理溶液中对活细胞实时观察.用不同固定剂和同一固定剂的不同浓度处理细胞;不加任何固定剂而直接在生理溶液中对细胞进行AFM成像.以戊二醛为固定剂并使用0.5%～1%的浓度固定细胞,后用缓冲溶液漂洗,再对细胞进行成像时可获得质量良好的图像.直接在生理溶液中进行观察,成像质量低于使用固定剂的细胞,但保持了细胞的生活原貌.在用原子力显微镜高分辨率观察生理条件下细胞的特点时,需要在制样与观测系统两方面进行改进.     

Surface N balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970-2030

Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970-2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification, N2O and NO emissions, and nitrate leaching from the root zone. Global NH3-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg·yr-1 between 1970 and 1995, and will further increase to 44 Tg·yr-1 in 2030. Similar developments are seen for N2O-N (2.0 Tg·yr-1 in 1970, 2.7 Tg·yr-1 in 1995 and 3.5 Tg·yr-1 in 2030) and NO-N emissions (1.1 Tg·yr-1 in 1970, 1.5Tg·yr-1 in 1995 and 2.0 Tg·yr-1 in 2030).     

Construction of novel single-cell screening system using a yeast cell chip for nano-sized modified-protein-displaying libraries

A novel screening system using a microchamber array chip was developed for construction of combinatorial nano-sized protein libraries in combination with yeast cell surface engineering. It is possible to place a single yeast cell into each microchamber, to observe its behavior, and to pick up the target cell. The microchamber array chip is referred to as a “yeast cell chip.” A single EGFP-displaying yeast cell could be detected, picked up by a micro-manipulator, and cultivated on agar medium. Furthermore, a catalytic reaction, the hydrolysis of fluorescein dioctanate, by a single yeast cell displaying Rhizopus oryzae lipase (ROL) was carried out in one microchamber. The ROL-encoding gene in a single ROL-displaying cell was amplified by PCR. These results demonstrate that this yeast cell chip in combination with cell surface engineering could be used as a tool in a high-throughput screening system not only for a single living cell and a whole-cell catalyst with a nano-sized protein cluster but also for modified nano-sized and functional protein molecules from protein libraries on the cell surface.     

A Computational Model of Soil Adhesion and Resistance for a Non-smooth Bulldozing Plate

1IntroductionAdhesive forces exist between soil and the surfacesof soil-engaging components[1,2].Soil adhesion increasesthe running resistance and energy consumption,andaffects the operating quality.Soil adhesion also reducesthe working productivity of terrain machines,even worseit makes terrain machines fail to run.Reducing theadhesive force of the soil-engaging machines will have aprofound influence for cultivation.Through theinvestigation of soil animals,we have found that soilanimals poss…     

Computational Model of Soil Adhesion and Resistance for a Non-smooth Bulldozing Plate

Adhesive forces exist between soil and the surfaces of soil-engaging components; they increase working resistance and energy consumption. This paper tries to find an approach to reduce the adhesion and resistance of bulldozing plate. A simplified mechanical model of adhesion and resistance between soil and a non-smooth bulldozing plate is proposed. The interaction force between moist soil and a non-smooth bulldozing plate is analyzed. The pressure and friction distribution on the bulldozing plate are computed, and the anti-adhesive effect of a corrugated bulldozing plate is simulated numerically. Numerical results show that the wavy bulldozing plate achieves an effective drag reduction in moist soil. The optimal wavy shape of the corrugated bulldozing plate with the minimal resistance is designed. The basic principle of reducing soil adhesion of the non-smooth surface is discovered.     

响应面法优化弗氏链霉菌S-221变种发酵培养基

用响应面法对弗氏链霉菌S-221变种液体发酵生产氨基酸的培养基进行了优化。首先,用全因子试验方法对相关影响因素的效应进行评价,并筛选出有显著效应的羽毛胨和蛋白胨两个因素,第2步用最陡爬坡实验逼近以上两因素最优水平。最后由中心组合设计法及响应面分析确定主要影响因素的最佳条件。在优化培养条件下,发酵液中氨基酸浓度从4.1g／100mL提高到6.412g／100mL。