New bibenzyls of the liverwort,Radula variabilis

Summary 3 new bibenzyls having a 7-membered heterocyclic ring have been isolated from the liverwort,Radula variabilis and their structures have been established to be1, 3 and5.     

Trichomonas hydrogenosomes contain the NADH dehydrogenase module of mitochondrial complex I

Hydrogenosomes are double-membraned ATP-producing and hydrogen-producing organelles of diverse anaerobic eukaryotes. In some versions of endosymbiotic theory they are suggested to be homologues of mitochondria, but alternative views suggest they arose from an anaerobic bacterium that was distinct from the mitochondrial endosymbiont. Here we show that the 51-kDa and 24-kDa subunits of the NADH dehydrogenase module in complex I, the first step in the mitochondrial respiratory chain, are active in hydrogenosomes of Trichomonas vaginalis. Like mitochondrial NADH dehydrogenase, the purified Trichomonas enzyme can reduce a variety of electron carriers including ubiquinone, but unlike the mitochondrial enzyme it can also reduce ferredoxin, the electron carrier used for hydrogen production. The presence of NADH dehydrogenase solves the long-standing conundrum of how hydrogenosomes regenerate NAD+ after malate oxidation. Phylogenetic analyses show that the Trichomonas 51-kDa homologue shares common ancestry with the mitochondrial enzyme. Recruitment of complex I subunits into a H2-producing pathway provides evidence that mitochondria and hydrogenosomes are aerobic and anaerobic homologues of the same endosymbiotically derived organelle.     

Escape of DNA from mitochondria to the nucleus in Saccharomyces cerevisiae

The migration of genetic information from ancestral prokaryotic endosymbionts into eukaryotic nuclei is thought to have had an important role in the evolution of mitochondria and chloroplasts. Here we describe an assay for the detection of movement of DNA between mitochondria and the nucleus in yeast. Because recombinant plasmid DNA replicates after transformation into mitochondria of yeast strains lacking endogenous mitochondrial DNA we were able to propagate the nuclear genetic marker URA3 in mitochondria. As expected, the wild-type URA3 gene in mitochondria failed to complement the uracil auxotrophy (Ura-) caused by a nuclear ura3 mutation. But selection of Ura+ prototrophs from a Ura- strain carrying URA3 on a plasmid in its mitochondria enabled us to detect plasmid movement to the nucleus. Conversely, as the plasmid used also contained the mitochondrial gene COX2 required for respiratory growth, we were able to set up corresponding selections to detect migration of DNA from the nucleus to the mitochondria. Our results show that, in yeast, DNA escapes from mitochondria and appears in the nucleus at a surprisingly high frequency (approximately 2 x 10(-5) per cell per generation). But the rate at which DNA makes the journey in the opposite direction--nucleus to mitochondria--is apparently at least 100,000 times less.     

一种用于结构动态过程数值模拟的广义有限元法

提出了一种能同时处理连续体和离散体动态过程的有限元法. 该法通过构造接触力模型, 将传统的离散元当做标准的一节点有限单元来看待. 新构造的一节点单元与常规有限单元具有同样物理特征, 包括应力和应变. 从而, 将离散元算法与有限元算法紧密结合在一起, 形成了统一的、与现有有限元系统兼容的广义有限元计算模型. 这种模型不仅简化了计算过程, 还可最大限度地发挥现有有限元代码的功能. 数值算例表明, 新方法可以更加有效地模拟大量离散体与连续体相互作用的复杂动力学过程.     

Inhibition of IgM antibody-mediated aggregation ofTrypanosoma gambiense in the presence of complement

This paper deals with the immune reaction betweenTrypanosoma gambiense and monoclonal IgM mouse antibody at equivalence with or without rabbit complement. Antibody-mediated trypanosome clumps formed in the absence of complement, and were readily dissociated by complement to become free. In the presence of complement, on the other hand,T. gambiense were not aggregated by the antibody. Free parasites adhered readily to cultured peritoneal macrophages. Complement-mediated dissociation of the clumped trypanosomes in the equivalence area released a large number of previously bound surface antigens. These antigens were capable of binding again to fresh IgM antibody. Experimental results further indicated that the complement system caused a functional alteration, changing the multivalent nature of the IgM antibody in the immune complex into a univalent one. This phenomenon is of great advantage to the infected host in clearing pathogens in vivo, as it allows more antibodies to attach to trypanosomes and subsequently initiate complement activity.     

Magnetic carbon

The discovery of nanostructured forms of molecular carbon has led to renewed interest in the varied properties of this element. Both graphite and C60 can be electron-doped by alkali metals to become superconducting; transition temperatures of up to 52 K have been attained by field-induced hole-doping of C60 (ref. 2). Recent experiments and theoretical studies have suggested that electronic instabilities in pure graphite may give rise to superconducting and ferromagnetic properties, even at room temperature. Here we report the serendipitous discovery of strong magnetic signals in rhombohedral C60. Our intention was to search for superconductivity in polymerized C60; however, it appears that our high-pressure, high-temperature polymerization process results in a magnetically ordered state. The material exhibits features typical of ferromagnets: saturation magnetization, large hysteresis and attachment to a magnet at room temperature. The temperature dependences of the saturation and remanent magnetization indicate a Curie temperature near 500 K.     

Early optical emission from the gamma-ray burst of 4 October 2002

Observations of the long-lived emission--or 'afterglow'--of long-duration gamma-ray bursts place them at cosmological distances, but the origin of these energetic explosions remains a mystery. Observations of optical emission contemporaneous with the burst of gamma-rays should provide insight into the details of the explosion, as well as into the structure of the surrounding environment. One bright optical flash was detected during a burst, but other efforts have produced negative results. Here we report the discovery of the optical counterpart of GRB021004 only 193 seconds after the event. The initial decline is unexpectedly slow and requires varying energy content in the gamma-ray burst blastwave over the course of the first hour. Further analysis of the X-ray and optical afterglow suggests additional energy variations over the first few days.     

Purification of mouse liver thymidylate synthetase by affinity chromatography using 10-methyl-5,8-dideazafolate as the affinant

Summary Thymidylate synthetase (methylenetetrahydrofolate: 2-deoxyuridine-5-monophosphate C-methyltransferase; EC 2.1.1.45) from neonatal mouse liver has been purified 714-fold by affinity chromatography on aminohexylsepharose bound 10-methyl-5,8-dideazafolate.Supported by grant CA22754, awarded by the National Cancer Institute, DHEW.