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201.
202.
Résumé Une méthode rapide pour l'extraction des pupes deGalleria mellonella hors de leur coconst est décrite. Le schema d'un appareil très simple pour le test biologique d'hormones est donné; il évite les brulures de la cuticule pupale.
Dr.A. de Loof gratefully acknowledges a mandate as Aangesteld Navorser of the N.F.W.O. This research was supported by the I.W.O.N.L. We wish to thank
Dr.P. Moerman for his help in the construction of the apparatus. 相似文献
Dr.A. de Loof gratefully acknowledges a mandate as Aangesteld Navorser of the N.F.W.O. This research was supported by the I.W.O.N.L. We wish to thank
Dr.P. Moerman for his help in the construction of the apparatus. 相似文献
203.
Summary Electrophoresis on acrylamide gel of basic proteins from the fungusAllomyces arbuscula (Butl.) yielded at least 16 bands. No differences were found between the banding-patterns of sporophyte and gametophyte. Extraction of histones from 1000 mg lyophilized mycelium and subsequent electrophoresis produced no bands. If histones are present at all, their concentration must be extremely low (< 5 µg/1000 mg material). 相似文献
204.
Quantum dynamical processes near the energy barrier that separates reactants from products influence the detailed mechanism by which elementary chemical reactions occur. In fact, these processes can change the product scattering behaviour from that expected from simple collision considerations, as seen in the two classical reactions F + H(2) --> HF + H and H + H(2) --> H(2) + H and their isotopic variants. In the case of the F + HD reaction, the role of a quantized trapped Feshbach resonance state had been directly determined, confirming previous conclusions that Feshbach resonances cause state-specific forward scattering of product molecules. Forward scattering has also been observed in the H + D(2) --> HD + D reaction and attributed to a time-delayed mechanism. But despite extensive experimental and theoretical investigations, the details of the mechanism remain unclear. Here we present crossed-beam scattering experiments and quantum calculations on the H + HD --> H(2) + D reaction. We find that the motion of the system along the reaction coordinate slows down as it approaches the top of the reaction barrier, thereby allowing vibrations perpendicular to the reaction coordinate and forward scattering. The reaction thus proceeds, as previously suggested, through a well-defined 'quantized bottleneck state' different from the trapped Feshbach resonance states observed before. 相似文献
205.
The dry landscape garden at Ryoanji Temple in Kyoto, Japan, a UNESCO world heritage site, intrigues hundreds of thousands of visitors every year with its abstract, sparse and seemingly random composition of rocks and moss on an otherwise empty rectangle of raked gravel. Here we apply a model of shape analysis in early visual processing to show that the 'empty' space of the garden is implicitly structured and critically aligned with the temple's architecture. We propose that this invisible design creates the visual appeal of the garden and was probably intended as an inherent feature of the composition. 相似文献
206.
Van Eerdewegh P Little RD Dupuis J Del Mastro RG Falls K Simon J Torrey D Pandit S McKenny J Braunschweiger K Walsh A Liu Z Hayward B Folz C Manning SP Bawa A Saracino L Thackston M Benchekroun Y Capparell N Wang M Adair R Feng Y Dubois J FitzGerald MG Huang H Gibson R Allen KM Pedan A Danzig MR Umland SP Egan RW Cuss FM Rorke S Clough JB Holloway JW Holgate ST Keith TP 《Nature》2002,418(6896):426-430
Asthma is a common respiratory disorder characterized by recurrent episodes of coughing, wheezing and breathlessness. Although environmental factors such as allergen exposure are risk factors in the development of asthma, both twin and family studies point to a strong genetic component. To date, linkage studies have identified more than a dozen genomic regions linked to asthma. In this study, we performed a genome-wide scan on 460 Caucasian families and identified a locus on chromosome 20p13 that was linked to asthma (log(10) of the likelihood ratio (LOD), 2.94) and bronchial hyperresponsiveness (LOD, 3.93). A survey of 135 polymorphisms in 23 genes identified the ADAM33 gene as being significantly associated with asthma using case-control, transmission disequilibrium and haplotype analyses (P = 0.04 0.000003). ADAM proteins are membrane-anchored metalloproteases with diverse functions, which include the shedding of cell-surface proteins such as cytokines and cytokine receptors. The identification and characterization of ADAM33, a putative asthma susceptibility gene identified by positional cloning in an outbred population, should provide insights into the pathogenesis and natural history of this common disease. 相似文献
207.
Hoogenraad CC Koekkoek B Akhmanova A Krugers H Dortland B Miedema M van Alphen A Kistler WM Jaegle M Koutsourakis M Van Camp N Verhoye M van der Linden A Kaverina I Grosveld F De Zeeuw CI Galjart N 《Nature genetics》2002,32(1):116-127
Williams syndrome is a neurodevelopmental disorder caused by the hemizygous deletion of 1.6 Mb on human chromosome 7q11.23. This region comprises the gene CYLN2, encoding CLIP-115, a microtubule-binding protein of 115 kD. Using a gene-targeting approach, we provide evidence that mice with haploinsufficiency for Cyln2 have features reminiscent of Williams syndrome, including mild growth deficiency, brain abnormalities, hippocampal dysfunction and particular deficits in motor coordination. Absence of CLIP-115 also leads to increased levels of CLIP-170 (a closely related cytoplasmic linker protein) and dynactin at the tips of growing microtubules. This protein redistribution may affect dynein motor regulation and, together with the loss of CLIP-115-specific functions, underlie neurological alterations in Williams syndrome. 相似文献
208.
209.
Effects of size and temperature on developmental time 总被引:17,自引:0,他引:17
Body size and temperature are the two most important variables affecting nearly all biological rates and times. The relationship of size and temperature to development is of particular interest, because during ontogeny size changes and temperature often varies. Here we derive a general model, based on first principles of allometry and biochemical kinetics, that predicts the time of ontogenetic development as a function of body mass and temperature. The model fits embryonic development times spanning a wide range of egg sizes and incubation temperatures for birds and aquatic ectotherms (fish, amphibians, aquatic insects and zooplankton). The model also describes nearly 75% of the variation in post-embryonic development among a diverse sample of zooplankton. The remaining variation is partially explained by stoichiometry, specifically the whole-body carbon to phosphorus ratio. Development in other animals at other life stages is also described by this model. These results suggest a general definition of biological time that is approximately invariant and common to all organisms. 相似文献
210.
Crystal structure of an ACh-binding protein reveals the ligand-binding domain of nicotinic receptors 总被引:45,自引:0,他引:45
Brejc K van Dijk WJ Klaassen RV Schuurmans M van Der Oost J Smit AB Sixma TK 《Nature》2001,411(6835):269-276
Pentameric ligand gated ion-channels, or Cys-loop receptors, mediate rapid chemical transmission of signals. This superfamily of allosteric transmembrane proteins includes the nicotinic acetylcholine (nAChR), serotonin 5-HT3, gamma-aminobutyric-acid (GABAA and GABAC) and glycine receptors. Biochemical and electrophysiological information on the prototypic nAChRs is abundant but structural data at atomic resolution have been missing. Here we present the crystal structure of molluscan acetylcholine-binding protein (AChBP), a structural and functional homologue of the amino-terminal ligand-binding domain of an nAChR alpha-subunit. In the AChBP homopentamer, the protomers have an immunoglobulin-like topology. Ligand-binding sites are located at each of five subunit interfaces and contain residues contributed by biochemically determined 'loops' A to F. The subunit interfaces are highly variable within the ion-channel family, whereas the conserved residues stabilize the protomer fold. This AChBP structure is relevant for the development of drugs against, for example, Alzheimer's disease and nicotine addiction. 相似文献