Structures from anomalous diffraction of native biological macromolecules

Crystal structure analyses for biological macromolecules without known structural relatives entail solving the crystallographic phase problem. Typical de novo phase evaluations depend on incorporating heavier atoms than those found natively; most commonly, multi- or single-wavelength anomalous diffraction (MAD or SAD) experiments exploit selenomethionyl proteins. Here, we realize routine structure determination using intrinsic anomalous scattering from native macromolecules. We devised robust procedures for enhancing the signal-to-noise ratio in the slight anomalous scattering from generic native structures by combining data measured from multiple crystals at lower-than-usual x-ray energy. Using this multicrystal SAD method (5 to 13 equivalent crystals), we determined structures at modest resolution (2.8 to 2.3 angstroms) for native proteins varying in size (127 to 1148 unique residues) and number of sulfur sites (3 to 28). With no requirement for heavy-atom incorporation, such experiments provide an attractive alternative to selenomethionyl SAD experiments.     

Hydration of macromolecules

Frozen protein and nucleic acid solutions at -35 degrees C show relatively narrow (100 milligauss) proton nuclear magnetic resonance signals which are assignable to water that is sufficiently mobile to reduce the dipolar broadening normally associated with solids. Hydration was found to be 0.3 to 0.5 gram of water per gram of protein. Nucleic acids are three to five times as hydrated as proteins. Conformational changes in solution produce detectable changes in linewidth or amount of "bound" water, or both. The very fact that the water signals can be observed by high resolution nuclear magnetic resonance suggests that it is not "ice-like" in any literal sense, although it is clearly less mobile than liquid water at the same temperature. A simple model is described which considers both surface hydration and trapped water.     

Far-ultraviolet stopped-flow circular dichroism

A stopped-flow circular dichroism instrument, with a total accessible wavelength range of 200 to 750 nanometers, has been constructed and provides a spectroscopic method for kinetic investigations of a wide array of fast reactions in which optical activity changes in absorbing regions are involved. An important biochemical application depends on the far-ultraviolet capability, which allows observation of the rapid alterations in backbone conformation associated with folding and unfolding reactions of proteins. Results obtained by following two such reactions at 222 nanometers represent direct monitoring by circular dichroism of rapid secondary structure changes in proteins.     

Nuclear reassembly excludes large macromolecules

Interphase nucleus and cytoplasm are distinct compartments, whose soluble macromolecular contents mix when the nuclear envelope disassembles at mitosis. To determine how their interphase identities are reestablished, fibroblasts were loaded with fluorescent dextrans and then allowed to divide. Large dextrans (molecular weight of 40,000 or more) were excluded from condensed mitotic chromosomes and from newly formed, postmitotic interphase nuclei. Therefore, postmitotic reassembly of the nucleus as a compartment distinct from cytoplasm occurs by exclusion not only of organelles but also of soluble macromolecules. This might occur by exclusion of macromolecules from condensed chromatin throughout mitosis and completion of nuclear envelope assembly before nuclear expansion.     

Intestinal uptake of macromolecules: effect of oral immunization

Animals were orally immunized with horseradish peroxidase and bovine serum albumin, and absorption of these antigens was studied. In comparison with controls, a consistent and significant decrease in peroxidase uptake was noted in both germ-free and conventional rats immunized with peroxidase; a similar decrease in serum albumin uptake was also noted in animals immunized with serum albumin. There was no difference in the uptake of an unrelated macromolecule. These observations suggest that local immunization interferes specifically with the intestinal uptake of macromolecular antigens.     

Plasma membranes of rat liver: isolation of lipoprotein macromolecules

Three high-denisity lipoprotein classes and one protein were separated from rat-liver plasma in membranes that had been treated with mild sonic oscillation. The lipoproteinis were separated and identified by techniques in which ultracentrifugation was used. Enzyme markers and electron-microscopic examination revealed membrane preparations essentially free of contaminating cellular partictulates.     

DNA: a model compound for solution studies of macromolecules

Well-defined, monodisperse, homologous series of oligonucleotides and DNA restriction fragments may now be produced and used as models of rigid and semirigid rodlike molecules in solution. Information from optical experiments on these model systems aids in the formulation and testing of theories of macromolecular dynamics in both dilute and concentrated solution.     

木工圆锯片CAD系统

论述了木工圆锯片ＣＡＤ系统,运行该系统可设计出较为完善,精确的木工圆锯片。     

循环经济发展再思考

传统经济增长模式忽视对环境的影响。现状越来越使我们认识到转变经济增长模式的迫切性与必要性。循环经济很好地统一了社会、经济、环境的协调可持续发展,成为中国乃至世界经济发展的必然选择。面对复杂的国情还有许多问题值得研究和思考。     

工业循环经济理论基础新探

工业循环经济兼顾了工业发展和环境保护,体现了人与自然的和谐共生。本文运用新兴的环境学与环境经济学原理解读了工业循环经济的产生和运行机制,从环境科学的角度进一步丰富和发展了其理论基础。     

植物环状RNA研究进展

环状RNA(circular RNA,circRNA)主要是真核细胞通过反向剪接作用使3′末端和5′末端共价结合而形成的一条单链非编码RNA分子,它是一种特殊的非编码RNA(noncoding RNA,ncRNA),在多种生物体中广泛存在.综述了植物中circRNA鉴定方法、分子特征以及潜在的生物学功能等方面,表明circRNA可能在生物胁迫、非生物胁迫以及生长和发育中发挥重要作用,并以动物中circRNA的研究进展为基础,对植物中circRNA的局限性和应用前景进行讨论.     

Reversible inhibition of beef heart cytochrome c oxidase by polyionic macromolecules

The basic proteins protamine (sulfate), histone, lysozyme, and ribonuclease were found to be potent inhibitors of mammalian heart muscle cytochromec oxidase. Their inhibitions were completely reversed in the presence of a strongly anionic polyglucose sulfate. With fresh rat heart muscle homogenates, Keili and Hartree type of beef heart muscle particulates, and deoxycholate-solubilized oxidase preparations, the reversible nature of the phenomenon was demonstrated with manometric and spectrophotometric assays for cytochrome c oxidase.     

初论区域农业循环系统

本文探索性地提出了区域农业循环系统的概念,构建了区域农业循环系统结构图,总结了区域农业循环系统的区域性、资源可循环性、多样性、整体性、以及"经济效益、生态效益、社会效益"综合实现性等主要特征,同时提出了构建区域农业循环系统的构建主体、"三个效益"的关系和外部性三个关键问题.     

Dielectrophoresis of macromolecules: determination of the diffusion constant of poly- -benzyl-L-glutamate

The translational diffusion constant of poly-gamma-benzyl-L-glutamate in ethylene dichloride was measured by dielectrophoresis. The method is rapid, precise to about +/- 5 percent, and yields values in good agreement with those obtained by standard methods.     

荆门市循环农业的建设重点

用循环农业的理论指导组织农业生产,目的是从根本上降低经济活动对环境的破坏,保护并改善农业生态环境,通过对资源的再利用(Reuse)和资源化(Recycle)来促使污染或废弃物减量化(Reduce),以实现经济的可持续发展。