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391.
Lekelia D. Jenkins 《Studies in history and philosophy of science》2010,41(1):75-85
This paper explores the evolution of a trading zone by organizing the case study of turtle excluder devices within the model proposed by Collins et al. (2007). The case study offers evidence that trading zones do evolve and that the concepts of enforced and fractionated trading zones hold practical utility for describing and defining the complexities of actual exchanges. In this case a trading zone evolved from enforced to fractionated and ultimately diverged into two trading zones. For each step of the evolution I describe the forces that drove these transitions. Finally, I present an adapted trading zone model that is conceptually a better fit for the turtle excluder device case study. 相似文献
392.
393.
Carl D. Marti 《西北部美国博物学家》2011,46(2)
An investigation of the diet of the Common Barn-owl ( Tyto alba ) on Antelope Island, Great Salt Lake, Utah, yielded four mammal species not previously known to occur on any island in the Great Salt Lake ( Microtus pennsylvanicus, M. montanus, Ondatra zibethicus , and a Sorex sp.). Two other species, known from other islands, were added to the list of fauna of Antelope Island ( Perognathus parvus and Reithrodontomys megalotis ). The barn owl diet on Antelope Island was remarkably like that of barn owls feeding in farmlands adjacent to the Great Salt Lake despite major vegetational differences. 相似文献
394.
395.
396.
Christian Dölle Marc Niere Emilia Lohndal Mathias Ziegler 《Cellular and molecular life sciences : CMLS》2010,67(3):433-443
Poly-ADP-ribose polymerases (PARPs) use NAD+ as substrate to generate polymers of ADP-ribose. We targeted the catalytic domain of human PARP1 as molecular NAD+ detector into cellular organelles. Immunochemical detection of polymers demonstrated distinct subcellular NAD+ pools in mitochondria, peroxisomes and, surprisingly, in the endoplasmic reticulum and the Golgi complex. Polymers did not
accumulate within the mitochondrial intermembrane space or the cytosol. We demonstrate the suitability of this compartment-specific
NAD+ and poly-ADP-ribose turnover to establish intra-organellar protein localization. For overexpressed proteins, genetically
endowed with PARP activity, detection of polymers indicates segregation from the cytosol and consequently intra-organellar
residence. In mitochondria, polymer build-up reveals matrix localization of the PARP fusion protein. Compared to presently
used fusion tags for subcellular protein localization, these are substantial improvements in resolution. We thus established
a novel molecular tool applicable for studies of subcellular NAD metabolism and protein localization. 相似文献
397.
Self peptides bound to self major histocompatibility complex (MHC) molecules have been implicated both in positive and in negative selection of T cells during intrathymic development. We report here that the novel MHC-restricted monoclonal antibody Y-Ae detects the MHC class II bound form of a major self peptide. Y-Ae binds approximately 12% of the relevant MHC class II molecules on self antigen presenting cells. The peptide detected by Y-Ae is one of several major peptides eluted from the MHC molecule. These data suggest that self peptides presented by self MHC class II molecules at densities sufficient to signal a CD4 T cell are of very limited complexity. Furthermore, as Y-Ae stains antigen presenting cells that mediate negative selection but not thymic cortical epithelial cells that drive positive selection, differential expression of self peptide:self MHC class II complexes may be a key feature of intrathymic selection. 相似文献
398.
R E Hill J Favor B L Hogan C C Ton G F Saunders I M Hanson J Prosser T Jordan N D Hastie V van Heyningen 《Nature》1991,354(6354):522-525
399.
The L-type voltage-dependent calcium channel is an important link in excitation-contraction coupling of muscle cells (reviewed in refs 2 and 3). The channel has two functional characteristics: calcium permeation and receptor sites for calcium antagonists. In skeletal muscle the channel is a complex of five subunits, alpha 1, alpha 2, beta, gamma and delta. Complementary DNAs to these subunits have been cloned and their amino-acid sequences deduced. The skeletal muscle alpha 1 subunit cDNA expressed in L cells manifests as specific calcium-ion permeation, as well as sensitivity to the three classes of organic calcium-channel blockers. We report here that coexpression of the alpha 1 subunit with other subunits results in significant changes in dihydropyridine binding and gating properties. The available number of drug receptor sites increases 10-fold with an alpha 1 beta combination, whereas the affinity of the dihydropyridine binding site remains unchanged. Also, the presence of the beta subunit accelerates activation and inactivation kinetics of the calcium-channel current. 相似文献
400.
W Dalemans P Barbry G Champigny S Jallat K Dott D Dreyer R G Crystal A Pavirani J P Lecocq M Lazdunski 《Nature》1991,354(6354):526-528
Cystic fibrosis is associated with a defect in epithelial chloride ion transport which is caused by mutations in a membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator). Heterologous expression of CFTR produces cyclicAMP-sensitive Cl(-)-channel activity. Deletion of phenylalanine at amino-acid position 508 in CFTR (delta F508 CFTR) is the most common mutation in cystic fibrosis. It has been proposed that this mutation prevents glycoprotein maturation and its transport to its normal cellular location. We have expressed both CFTR and delta F508 CFTR in Vero cells using recombinant vaccinia virus. Although far less delta F508 CFTR reached the plasma membrane than normal CFTR, sufficient delta F508 CFTR was expressed at the plasma membrane to permit functional analysis. delta F508 CFTR expression induced a reduced activity of the cAMP-activated Cl- channel, with conductance, anion selectivity and open-time kinetics similar to those of CFTR, but with much greater closed times, resulting in a large decrease of open probability. The delta F508 mutation thus seems to have two major consequences, an abnormal translocation of the CFTR protein which limits membrane insertion, and an abnormal function in mediating Cl- transport. 相似文献