The subunit structure of bovine brain 14-3-2

Two aspects of the subunit structure of the bovine brain specific protein 14-3-2 have been examined. On the one hand, native 14-3-2 has been separated into two fractions by hydroxylapatite chromatography. One eluted at the same position when chromatographed on the same column, while the other redistributed into the same two fractions again. Amino acid analysis of these two forms of 14-3-2 gave results that were not significantly different under the condition of analysis. Furthermore, when each peak was subjected to cyanogen bromide cleavage, very similar elution profiles of the resultant fragments were obtained. The two pools also cross-reacted with antiserum to 14-3-2. Reaction of purified 14-3-2 with dimethylsuberimidate caused the formation of covalently bound protein units of 100,000 molecular weight when measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis, as opposed to the 50,000 minimal molecular weight normally detected. On the other hand, analysis of the soluble tryptic peptides of S-[14C]carboxymethyl 14-3-2 yielded only three distinct radioactive peptides, each with one residue of S-carboxymethylcysteine whereas 8 are expected on the basis of the amino acid composition of the 50,000 molecular weight polypeptide chains. Thermolysin digestion of a similarly modified 14-3-2 preparation yielded all of the radioactivity in 5 S-carboxymethylcysteine-containing peptides. The partial amino acid sequence of these peptides indicates that they represent 4 unique areas of the polypeptide chain. Since 8 such peptides were expected, that is, double the number found, the minimum structural unit of the protein must be of 25,000 molecular weight. The results of these experiments do not permit distinction between a duplication of the structure within a single polypeptide chain or the alternate possibility of two polypeptide chains bound by unusually strong non-covalent bonds. These results suggest that 14-3-2 is a covalently linked dimer of 25,000 mol.wt. units that can aggregate to form larger species of 100,000 mol.wt. and higher.     

A mass spectrometry and surface enhanced Raman spectroscopy study of the interaction between linear carbon chains and noble metals

Linear carbon chains (LCCs) contain sp hybridization either as alternating triple and single bonds (polyynes) or with consecutive double bonds (cumulenes). They are detected here in solution by a combined mass spectrometry (MS) and surface enhanced Raman scattering approach, and new insight into the carbon structures, formed after performing pulsed laser ablation of a polycrystalline graphite rod in water stabilized by the presence of metals is given. The possibility to establish a LCC-metal bond is also investigated by carrying out atmospheric pressure matrix assisted laser desorption ionization MS experiments on copper and silver polyynides. It was found that while the interaction of metal colloids with LCCs results mainly in a weak bond, polyynides appear as true organometallic compounds in which the metal is covalently bonded to the LCCs.     

A 2.5-GHz DDFS-PLL With 1.8-MHz Bandwidth in 0.35-$mu$m CMOS

A wideband frequency synthesizer architecture is presented. The proposed topology employs a direct digital frequency synthesizer (DDFS) to control the output frequency of an offset-PLL. In this way, the synthesizer features a very fine frequency resolution, 24 Hz, as in delta-sigma fractional-N PLLs, but without being affected by the quantization-induced phase noise. This, in turn, allows enlarging the loop bandwidth. The frequency synthesizer is designed to be employed as a direct modulator for Bluetooth transmitter in a low-cost 0.35-mum CMOS technology. At 2.5GHz it achieves 1.8-MHz bandwidth, while the settling time within 30ppm for an 80-MHz step is 3 mus. The integrated phase noise gives less than 1 degree of rms phase error and the worst-case spur is 48dBc at 1 MHz, well below the specifications. Power dissipation is 120 mW for the PLL core, 50 mW for the DDFS plus DACs, and 19 mW for the GFSK modulator.     

Double-stranded deoxyribonucleic acid binds to HLA class II molecules and inhibits HLA class II-mediated antigen presentation

CD4+ T cells proliferating in response to purified double-stranded deoxyribonucleic acid (dsDNA) have been recently demonstrated in peripheral blood mononuclear cells of patients with systemic lupus erythematosus. Their activation was inhibited by anti-HLA class II (HLA-II) monoclonal antibodies; thus, the existence of a molecular interaction between dsDNA and HLA-II is conceivable. In this report we show that dsDNA specifically bind to HLA-II. After preincubating cells with purified dsDNA or synthetic oligonucleotides, dsDNA was detected on the cell membrane and in the lysates of HLA-II+ but not of isogenic HLA-II- cell lines. We demonstrate that dsDNA binding inhibits that of a specific peptide to HLA-II. Mixed lymphocyte reaction and antigen-specific T cell proliferation were inhibited by the preincubation of stimulator cells or antigen-presenting cells with dsDNA. These results suggest the existence of a novel mechanism of down-modulation of the CD4+ T cell function generated by lack of stimulation due to the HLA-II presenting molecules being "occupied" by dsDNA.     

TBM法隧道掘进综述

由于采用了最先进的隧道施工技术 ,尤其是隧道掘进机 (ＴＢＭ )施工技术 ,高度机械化特别是管理方式以及相关的国家政策 ,使西方国家的大型地下工程和深埋长大隧道成为可能。这些先进的隧道施工技术在使用中通过相关各方坚韧不拔的努力克服了所产生的问题。为了成功引进ＴＢＭ技术及其施工方法 ,战略性的、系统的、统一的引进方法极为重要。中国的西部大开发可为这些施工方法的实施提供独一无二的机遇 ,其规模比西方国家实施的任何国家级工程项目都大。通过吸取西方国家在过去四十年中所积累的ＴＢＭ法隧道施工的技术经验 ,可以成功实现ＴＢ…     

Nature and Extent of Domestic Construction Program Outsourcing

The sourcing of a construction program has always been a fluid process for many construction owners. A construction owner must balance the performance of all construction functions between internal staff and external service providers. Described herein are recent sourcing trends of construction programs identified through a survey of nonresidential construction owners. The survey data is representative of 170 respondents with varying demographic characteristics that account for about $72 billion in annual construction spending. Included are outsourcing trends of specific functions across the construction lifecycle and the sourcing strategy employed for each. A comparison of the outsourcing volume reported and the sourcing strategy employed is presented. A clear relationship between the amount of outsourcing and the sourcing strategy employed for the performance of construction is shown. The paper provides the academic community with new outsourcing data for construction lifecycle functions. It also provides contractors with new information about the current behavior of construction owners while providing owners with a better understanding of the relationship between sourcing and outsourcing.