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121.
Species-specific composition of free amino acids on the leaf surface of fourSenecio species 总被引:1,自引:1,他引:0
The specificity of the chemical composition of the leaf surface of fourSenecio species was studied in order to understand the host selection ofTyria jacobaeae, a monophagous moth that hasSenecio jacobaea as its principal host plant. Pyrrolizidine alkaloids characteristic forSenecio species were not detected in water and sulfuric acid extracts of the leaf surface ofSenecio jacobaea. Water extracts of the leaf surfaces ofS. jacobaea, S. vulgaris, S. viscosus, andS. sylvaticus contained low concentrations of free amino acids. The proportions of these amino acids were very different from those inside the leaf tissues. In a discriminant analysis, the four species could be completely separated on the basis of the relative proportions of amino acids on the leaf surface. 相似文献
122.
Jean-Pierre Duval 《Theoretical computer science》1979,9(1):17-26
We study the relationship between the global periodicity of a word and its (local) repetitions, that is to say its successive equal factors.Our main result generalizes the theorem of Cesari Vincent according to which the period of a word is the maximum of the minimal repetitions. Our generalization is twofold, it does not take account of any sides to define repetitions (the above result does) and calculates the maximum only on a special set of points. It allows a sharpened version of the solution to a problem settled by Schützenberger in which the theorem of Cesari Vincent originates. 相似文献
123.
124.
Measurements have been made of the length changes due to self-irradiation damage at 4.2 K for over 1300 h in a U-Pu-Mo bcc alloy (containing 20 at% plutonium and 15 at% molybdenum) stabilized by quenching. These are the first measurements of this type carried out on a bcc alloy. The initial rate of increase of δl/l was If it is assumed that each α desintegration forms 1800 Frenkel pairs, it is found that Frenkel pairs have a formation volume equal to 0.5 atomic volume. 相似文献
125.
Jean-Pierre Bastide Bernard Bonnetot Jean-Marie Létoffé Pierre Claudy 《Materials Research Bulletin》1980,15(12):1779-1787
The structural relationships in magnesium hydride have been studied under P-T conditions up to 80 kbar and 900°C. α-MgH2 of rutile structure in normal conditions transforms into two new phases under high pressures : β-MgH2 and γ-MgH2 respectively with a hexagonal (pseudocubic) and an orthorhombic unit-cell structure·β-MgH2 maybe related to a fluorite type form (with an eight-coordination for Mg) transforming when releasing pressure into γ-MgH2 of α-PbO2 type (with a six-coordination for Mg). The density of α-MgH2 and γ-MgH2 are very similar but the density of the β-MgH2 fluorite form is some 25 % greater than that of the rutile type. Thus MgH2 seems to exhibit under high pressure conditions the typical behavior of number of rutile type compounds MX2 such as fluorides or oxides. 相似文献
126.
127.
Jean-Pierre Bonnet Jean-Claude Grenier Marc Onillon Michel Pouchard Paul Hagenmuller 《Materials Research Bulletin》1979,14(1):67-75
The type of point defects in non-stoichiometric Ca2LaFe3O8+x ferrite has been studied by measuring the variation of electrical conductivity with oxygen partial pressure at various temperatures. Several ordering possibilities occur. The oxygen atoms inserted, mostly 1-charged, have a strong tendency to couple at sufficient oxygen pressure and at low temperature. Interstitial oxygen atoms in the lattice vacancies induce structural evolution as non-stoichiometry becomes significant enough. 相似文献
128.
Quinton L Le Caer JP Phan G Ligny-Lemaire C Bourdais-Jomaron J Ducancel F Chamot-Rooke J 《Analytical chemistry》2005,77(20):6630-6639
The standard analytical procedure for screening the proteomic profile of a venom often relies on an appropriate combination of sample extraction, electrophoresis, reversed-phase high-performance liquid chromatography, mass spectrometry, and Edman degradation. We present in this study a new approach for venom screening based on Fourier transform mass spectrometry (FTMS) analysis directly on the crude venom. The venom chosen is a unique sample from Atractaspis irregularis, a species never studied at the molecular level previously. This snake belongs to the Atractaspidae family that is known to produce highly toxic venoms containing endothelin-like peptides called sarafotoxins (SRTXs). Nanoelectrospray-FTMS spectrum of the crude venom allowed the identification of 60 distinct compounds with molecular masses from 600 to 14,000 Da, which would have been impossible without the resolution of this kind of instrument. De novo sequencing within the entire venom confirmed the sequences of two new families of sarafotoxins, whose precursors had been cloned, and allowed the characterization of a third one. One particularly interesting point was that the propolypeptides appeared processed not in one unique compound, but rather in different length molecules ranging from 15 for the shorter to 30 amino acids for the longer. Moreover, our results clearly establish that in the case of A. irregularis only one copy of mature sarafotoxin emerges from each precursor, which is a totally different organization in comparison of other precursors of SRTXs. 相似文献
129.
130.
Projection of transmembrane helices using a Uniform B-spline Algorithm is a tool for the visualization of interactions between helices in membrane proteins. It allows the user to generate projections of 3D helices, no matter what their deviations from a canonical helix might be. When associated with adapted coloring schemes it facilitates the comprehension of helix-helix interactions. Examples of transmembrane proteins were chosen to illustrate the advantages that this method provides. In the glycophorin A dimer we can easily appreciate the structural features behind homodimerisation. Using the structure of the fumarate reductase we analyze the contact surfaces inside a helical bundle and thanks to structures from a molecular dynamics simulation we see how modifications in structure and electrostatics relate to their interaction. We propose the use of this tool as an aid to the visualization and analysis of transmembrane helix surfaces and properties. 相似文献