Some aspects of the NMR-spectra of aporphine and phenanthrene alkaloids

Summary The C-11 proton of an aprophine possessing a C-1,2 methylenedioxy group falls relatively upfield between 7.47 and 7.86. Additionally, the i.c.s. for the two protons of the methylenedioxy group is large (4–12 Hz). The presence of a methylenedioxy at C-3,4 in a phenanthrene alkaloid also results in an upfield shift ( 8.95–9.00) of the C-5 proton.This project was supported by NIH research grant No. HL-12971, awarded by the National Heart and Lung Institute, PHS/DHEW.     

Some aspects of the early development and implantation of the mammalian egg

Summary The early development and implantation of the mammalian egg is described for various species and the differing and often contradictory solutions proposed by different authors for the many problems arising from their investigations are exposed, compared and discussed.     

The superoxide-generating NADPH oxidase: structural aspects and activation mechanism

Flavocytochrome b ₅₅₈ is the catalytic core of the respiratory-burst oxidase, an enzyme complex that catalyzes the NADPH-dependent reduction of O₂ into the superoxide anion O₂ ^- in phagocytic cells. Flavocytochrome b ₅₅₈ is anchored in the plasma membrane. It is a heterodimer that consists of a large glycoprotein gp91phox (phox for phagocyte oxidase) (β subunit) and a small protein p22phox (α subunit). The other components of the respiratory-burst oxidase are water-soluble proteins of cytosolic origin, namely p67phox, p47phox, p40phox and Rac. Upon cell stimulation, they assemble with the membrane-bound flavocytochrome b ₅₅₈ which becomes activated and generates O₂ ^-. A defect in any of the genes encoding gp91phox, p22phox, p67phox or p47phox results in chronic granulomatous disease, a genetic disorder characterized by severe and recurrent infections, illustrating the role of O₂ ^- and the derived metabolites H₂O₂ and HOCl in host defense against invading microorganisms. The electron carriers, FAD and hemes b, and the binding site for NADPH are confined to the gp91phox subunit of flavocytochrome b ₅₅₈ . The p22phox subunit serves as a docking site for the cytosolic phox proteins. This review provides an overview of current knowledge on the structural organization of the O₂ ^--generating flavocytochrome b ₅₅₈ , its kinetics, its mechanism of activation and the regulation of its biosynthesis. Homologues of gp91phox, called Nox and Duox, are present in a large variety of non-phagocytic cells. They exhibit modest O₂ ^--generating oxidase activity, and some act as proton channels. Their role in various aspects of signal transduction is currently under investigation and is briefly discussed. Received 28 May 2002; received after revision 20 June 2002; accepted 24 June 2002     

Some aspects of the hydrolysis of phosphomonoesters by homogenates of growing and regressing mesonephroi in chick embryos

Résumé L'activité de la phosphatase acide envers le-glycérophosphate et le phénylphosphate a été comparée sous des conditions variées afin de constater si ces deux actions reflètent celle de molécules enzymatiques pareilles ou différentes pendant la croissance et la régression du mésonéphros chez l'embryon de poulet. Pour élucider cette question, on a étudié les effets de la température au pH 5, et du versène, et l'influence d'un substratum sur l'hydrolyse. Les résultats de ces recherches indiquent que la même enzyme pourrait être responsable de l'hydrolyse de ces 2 substrats.

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This investigation was supported by NIH Training Grant No. HD-00012.     

Some comparisons of the relative power of simple tests for structural change in regression models

The power of Chow, linear, predictive failure and cusum of squares tests to detect structural change is compared in a two-variable random walk model and a once-for-all parameter shift model. In each case the linear test has greatest power, followed by the Chow test. It is suggested that the linear test be used as the basic general test for structural change in time series data, and tests of forecasting performance be confined to the last few observations. Analysis of recursive residuals and recursive parameter estimates should be regarded as forms of exploratory data analysis and tools for understanding discrepancies with previous results rather than a basis for formal tests of structural change.     

高速铁路用水泥乳化沥青浆体的物理结构

基于硬化硅酸盐水泥浆体的Powers理论和水泥乳化沥青浆体的配合比,通过理论计算和X射线衍射(XRD)、扫描电子显微镜(SEM)、能量色散X射线谱仪(EDAX)等相分析方法,分析了硬化水泥乳化沥青浆体的物相组成与微结构.结果表明,硬化水泥乳化沥青浆体的物相组成与微结构取决于沥灰比和水灰比.提出了表征硬化水泥乳化沥青浆体物理结构的两种结构模型,以沥青为连续相、水泥相为分散相的有机-无机复合胶凝体结构模型—I型模型;以水泥相为基体、沥青嵌入其中的无机-有机复合胶凝体结构模型—II型模型.为深入分析高速铁路板式无砟轨道结构中水泥乳化沥青砂浆的微结构参数和力学性能及其衰变规律奠定了基础.     

亚高山针叶林群落系统的生态学过程和持续性机制

森林生态系统由于其复杂的物质循环与能量转化通道，直接参与地图一生物圈问的生物地球化学循环。因此，对森林生态系统结构与功能的研究一直是研究全球生态环境问题的核心。目前在这个研究领域的共识是：对生态系统功能的了解首先是基于对系统组分过程结构和动态的理解，而生态系统多功能的持续性机制在于确保组成系统的各组分过程结构的维持和良好的协调。在森林群落生态系统中，最基本的植物、生态学过程是能流传输(transfer)和分配(partitioning)过程，碳、养分和水循环过程，生态位的相对稳定和分化过程以及植物的生长，死亡和更新过程。川西亚高山针叶林是我国西部目前唯一保存良好的天然森林。除了它重要的、不可替代的生态、经济和社会地位外，从生态系统本身以及与全球气候变化的联系上，地处高寒环境下的川西亚高山针叶林生态系统有其独特之处：相对简单的层次结构和种丰富度，清晰的更新和演替规律，有意义的地质、气候和区系历史，巨大的土壤冷冻碳库，更加分化的结构和功能类型，复杂的地形、地貌组合以及生态位的多样性等。这些特征一方面给系统生态过程研究带来许多挑战性的问题，另一方面为研究植被动态过程以及植被与气候变化相互作用提供了一个天然实验室。     

升高CO2浓度和温度对针叶林的影响以及在川西亚高山针叶林研究中的展望

以CO2浓度和温度升高为主要特征的全球气候变化受到了世界各国科学家们的普遍关注。目前已经有大量关于森林生态系统对全球变化响应的研究报道和综述性文章,涉及分子、生理生态、种群和群落生态以及区域和全球尺度等微观和宏观领域的研究内容,因而要想对森林生态系统对全球变化的响应研究进行全面的综述是相当困难的。因此,本文只简要评述了森林生态系统对升高CO2浓度和温度响应研究中的诸如CO2浓度和温度升高对森林生长和生产力的影响、森林生态系统物种组成和多样性对升高CO2浓度和温度的响应、植被变化与全球碳循环的互动以及气候变化与森林生态系统生物地球化学循环的关系等几个热点问题。川西亚高山针叶林区为我国的第二大林区,地处高山峡谷地带,是全球变化的敏感地带。相对简单的植物群落结构、较低的物种丰富度和多样性、巨大的冷冻土壤碳库、不同演替阶段和功能的植物群落组合以及分布于林线附近的邻接效应等为研究针叶林系统对升高CO2浓度和温度的响应提供了良好的天然实验室。针叶林生产力、植物群落物种组成和多样性以及土壤碳氮过程等对升高CO2浓度和温度的响应对于预测未来气候变化下针叶林系统的生态过程具有重要意义。     

Cellular and molecular aspects of drugs of the future: oxaliplatin

Oxaliplatin (Eloxatine) is a third-generation platinum compound which has shown a wide antitumour effect both in vitro and in vivo, a better safety profile than cisplatin and a lack of cross-resistance with cisplatin and carboplatin. In this scenario, oxaliplatin may represent an innovative and challenging drug extending the antitumour activity in diseases such as gastrointestinal cancer that are not usually sensitive to these coordination complexes. Oxaliplatin has a non-hydrolysable diaminocyclohexane (DACH) carrier ligand which is maintained in the final cytotoxic metabolites of the drug. Like cisplatin, oxaliplatin targets DNA producing mainly 1,2-GG intrastrand cross-links. The cellular and molecular aspects of the mechanism of action of oxaliplatin have not yet been fully elucidated. However, the intrinsic chemical and steric characteristics of the DACH-platinum adducts appear to contribute to the lack of cross-resistance with cisplatin. To date, mismatch repair and replicative bypass appear to be the processes most likely involved in differentiating the molecular responses to these agents. Received 15 March 2002; received after revision 13 May 2002; accepted 21 May 2002 RID="*" ID="*"Corresponding author.     

Cellular and molecular aspects of drugs of the future: meropenem

Meropenem, first synthesized in the late eighties, has become one of the most important beta-lactam antibiotics of the carbapenem subclass used for the treatment of a variety of life-threatening infections. Due to its unique chemical structure, meropenem is not inactivated by the kidney dehydropeptidase I and the majority of microbial beta-lactamases. Its antimicrobial activity is based on its high affinity for the majority of cell wall-synthesizing enzymes, the so-called penicillin-binding proteins, of Gram-positive and -negative bacteria. However, bacteria have evolved several approaches to resist meropenem: (i) by reducing the affinity of the penicillin-binding proteins for the antibiotics, (ii) by decreasing the permeability of the outer membrane of Gram-negative bacteria, (iii) by using efflux pumps, and (iv) by activating zinc-dependent carbapenemases. Meropenem has a low toxicity profile and, in contrast to imipenem, no central nervous system toxicity.