排序方式: 共有86条查询结果,搜索用时 6 毫秒
81.
Stephan M. Rosentreter Roger W. Davenport Jürgen Lschinger Julita Huf Jürgen Jung Friedrich Bonhoeffer 《Developmental neurobiology》1998,37(4):541-562
Although molecular gradients have long been postulated to play a role in the development of topographic projections in the nervous system, relatively little is known about how axons evaluate gradients. Do growth cones respond to concentration or to slope? Do they react suddenly or gradually? Is there adaptation? In the developing retinotectal system, temporal retinal ganglion cell axons have previously been shown to avoid repellent cell-surface activities distributed in gradients across the optic tectum. We confronted temporal retinal axons with precisely formed striped linear gradients of repellent tectal membranes and of two candidate repellent molecules, ephrin-A2 and -A5. Axons entered gradient stripes independently of their slope and extended unhindered in the uphill direction until they suddenly avoided an apparent threshold concentration of repellent material that was independent of slope. This critical concentration was similar in both linear and nonlinear gradients, and hence independent of gradient shape. When gradients of identical slope were formed on different basal levels of repellent material, axons grew uphill for a fixed increment of concentration, possibly measured from the lowest point of the gradient, rather than up to a fixed absolute concentration. The speed of growth cones was not affected by repellent unstriped gradients below the critical concentration level. Similar results were found with membranes from cell lines stably transfected with either ephrin-A5 or ephrin-A2, two previously identified growth cone repellent cell-surface proteins. These data suggest that growth cones or axons can integrate guidance information over large distances, probably by a combined memory and adaptation mechanism. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 541–562, 1998 相似文献
82.
Tyrosine-rich conopeptides affect voltage-gated K+ channels 总被引:1,自引:0,他引:1
Imperial JS Chen P Sporning A Terlau H Daly NL Craik DJ Alewood PF Olivera BM 《The Journal of biological chemistry》2008,283(34):23026-23032
Two venom peptides, CPY-Pl1 (EU000528) and CPY-Fe1 (EU000529), characterized from the vermivorous marine snails Conus planorbis and Conus ferrugineus, define a new class of conopeptides, the conopeptide Y (CPY) family. The peptides have no disulfide cross-links and are 30 amino acids long; the high content of tyrosine is unprecedented for any native gene product. The CPY peptides were chemically synthesized and shown to be biologically active upon injection into both mice and Caenorhabditis elegans; activity on mammalian Kv1 channel isoforms was demonstrated using an oocyte heterologous expression system, and selectivity for Kv1.6 was found. NMR spectroscopy revealed that the peptides were unstructured in aqueous solution; however, a helical region including residues 12-18 for one peptide, CPY-Pl1, formed in trifluoroethanol buffer. Clones obtained from cDNA of both species encoded prepropeptide precursors that shared a unique signal sequence, indicating that these peptides are encoded by a novel gene family. This is the first report of tyrosine-rich bioactive peptides in Conus venom. 相似文献
83.
Bayrhuber M Vijayan V Ferber M Graf R Korukottu J Imperial J Garrett JE Olivera BM Terlau H Zweckstetter M Becker S 《The Journal of biological chemistry》2005,280(25):23766-23770
Conkunitzin-S1 (Conk-S1) is a 60-residue neurotoxin from the venom of the cone snail Conus striatus that interacts with voltage-gated potassium channels. Conk-S1 shares sequence homology with Kunitz-type proteins but contains only two out of the three highly conserved cysteine bridges, which are typically found in these small, basic protein modules. In this study the three-dimensional structure of Conk-S1 has been solved by multidimensional NMR spectroscopy. The solution structure of recombinant Conk-S1 shows that a Kunitz fold is present, even though one of the highly conserved disulfide cross-links is missing. Introduction of a third, homologous disulfide bond into Conk-S1 results in a functional toxin with similar affinity for Shaker potassium channels. The affinity of Conk-S1 can be enhanced by a pore mutation within the Shaker channel pore indicating an interaction of Conk-S1 with the vestibule of potassium channels. 相似文献
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Tadeusz Antczak Julita Mrowiec-Białoń Stanisław Bielecki Andrzej B. Jarzębski Janusz J. Malinowski Andrzej I. Lachowski Edward Galas 《Biotechnology Techniques》1997,11(1):9-11
The lipase ofMucor javanicus (nowM. circinelloides) entrapped in silica matrix by the sol-gel method esterified primary and secondary alcohols with conversions ranging from
30 to 35% and 10 to 15%, respectively. Loss in activity of the preparations after incubation at 100°C for 1 h with petroleum
ether, dodecane, 1-heptanol or oleyl alcohol was about half of that observed for the native lipase. 相似文献
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