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891.
An experimental procedure and method of analysis are presented for calibration of a thin-beam force transducer. The beam transducer
can be produced and calibrated with a minimum coefficient of 10 ng (10−5 dyne) force per micron (10−4 cm) deflection, i.e.,k
B∼0.1 dyne/cm. Since beam deflections on the order of 0.1 μm can be detected, forces of a few nanograms can be resolved. Such
forces are common in mechanical experiments on microscopic bodies, e.g., biological cells, artificial membrane capsules, droplets,
etc. 相似文献
892.
Neuropeptide Y (NPY) is present in both extrinsic sympathetic adrenergic nerve terminals and intrinsic nerves of the gastrointestinal (GI) tract. Based on this localization a number of functions have been attributed to GI NPY including regulation of blood flow, intestinal fluid and electrolyte transport, and motility. There is nothing currently known, however, about the regulation of its secretion from GI nerves. The effect of cholinergic agonists and antagonists on secretion of NPY immunoreactivity (NPY-IR) from the isolated perfused rat stomach was investigated in the present study. Perfusate samples were extracted and concentrated on SepPak cartridges. Basal levels of NPY-IR varied between 98 and 147 fmol/min. Release was stimulated by high potassium concentrations (50 mM) and acetylcholine (ACh; 1 microM). ACh-induced secretion was unaffected by atropine, but inhibited by hexamethonium. Further evidence for a nicotinic component in the regulation of NPY-IR secretion was obtained by the finding of hexamethonium-induced reduction in basal secretion and stimulation of secretion by 1,1-dimethyl-4-phenyl-piperazinium (DMPP). In conclusion, cholinergic agonists and antagonists can modulate gastric NPY-IR secretion, and the cholinergic stimulatory effects are probably mediated via nicotinic receptor stimulation at the level of the intrinsic ganglia. 相似文献
893.
Pyridoxal kinase has been purified 2000-fold from pig brain. The enzyme preparation migrates as a single protein and activity band on analytical gel electrophoresis. The interactions of the substrate pyridoxal and the inhibitor N-dansyl-2-oxopyrrolidine (dansyl = 5-dimethylaminonaphthalene-1-sulfonyl) with the catalytic site were examined by means of fluorescence spectroscopy. The increase in emission anisotropy that follows the binding of pyridoxal to the kinase was used to determine the equilibrium dissociation constant. Pyridoxal kinase binds one molecule of substrate with a Kd = 11 microns at pH 6. The emission anisotropy spectrum of bound pyridoxal reveals that the substrate is not rigidly trapped by the protein matrix. N-Dansyl-2-oxopyrrolidine is a competitive inhibitor with respect to ATP at saturating concentrations of pyridoxal. It binds to the enzyme with a dissociation constant of 6 microns. N-Dansyl-2-oxopyrrolidine is immobilized by strong interactions with the enzyme, but it is displaced from the catalytic site by ATP. The results are consistent with the hypothesis that N-dansyl-2-oxopyrrolidine binds at the nucleotide binding site of pyridoxal kinase. 相似文献
894.
Hon-Kai Kwok 《农业工程》2009,29(6):341-346
In a mixed forest in Hong Kong, the foraging ecology of nine species of insectivorous birds was studied. Leaves and branches of diameters smaller than 2 cm were the most frequently searched microhabitats. Gleaning was the most frequently used foraging method. Apart from Blue-winged Minla and Japanese White-eye, no two species used similar proportions of vertical strata and microhabitats at the same time. Bird species using similar proportion of microhabitats were foraging in different proportion of vertical strata. This niche segregation enabled the bird species to coexist in the same habitat. Velvet-fronted Nuthatch differed from other species by its more frequent use of branches of diameters larger than 2 cm and tree trunks. This might be one of the reasons why this exotic species successfully established a breeding population in the study area. 相似文献
895.
Arabidopsis homologs of a c-Jun coactivator are present both in monomeric form and in the COP9 complex, and their abundance is differentially affected by the pleiotropic cop/det/fus mutations. 总被引:6,自引:1,他引:5
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S F Kwok R Solano T Tsuge D A Chamovitz J R Ecker M Matsui X W Deng 《The Plant cell》1998,10(11):1779-1790