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991.
Susanne Becker Heike Schneider Georgios Scheiner-Bobis 《European journal of biochemistry》2004,271(19):3821-3831
The peptide sequence DSYG(893-896) of the sheep sodium pump alpha 1 subunit is highly conserved among all K(+)-transporting P-type ATPases. To obtain information about its function, single mutations were introduced and the mutants were expressed in yeast and analysed for enzymatic activity, ion recognition, and alpha/beta subunit interactions. Mutants of Ser894 or Tyr895 were all active. Conservative phenylalanine and tryptophan mutants of Tyr895 displayed properties that were similar to the properties of the wild-type enzyme. Replacement of the same amino acid by cysteine, however, produced heat-sensitive enzymes, indicating that the aromatic group contributes to the stability of the enzyme. Mutants of the neighbouring Ser894 recognized K(+) with altered apparent affinities. Thus, the Ser894-->Asp mutant displayed a threefold higher apparent affinity for K(+) (EC(50) = 1.4 +/- 0.06 mm) than the wild-type enzyme (EC(50) = 3.8 +/- 0.33 mm). In contrast, the mutant Ser894-->Ile had an almost sixfold lower apparent affinity for K(+) (EC(50) = 21.95 +/- 1.41 mm). Mutation of Asp893 or Gly896 produced inactive proteins. When an anti-beta 1 subunit immunoglobulin was used to co-immunoprecipitate the alpha 1 subunit, neither the Gly896-->Arg nor the Gly896-->Ile mutant could be visualized by subsequent probing with an anti-alpha 1 subunit immunoglobulin. On the other hand, co-immunoprecipitation was obtained with the inactive Asp893-->Arg and Asp893-->Glu mutants. Thus, it might be that Asp893 is involved in enzyme conformational transitions required for ATP hydrolysis and/or ion translocation. The results obtained here demonstrate the importance of the highly conserved peptide DSYG(893-896) for the function of alpha/beta heterodimeric P-type ATPases. 相似文献
992.
Respiratory allergies represent a failure to generate nonpathogenic responses to innocuous foreign materials. Herein we assessed the role of the sensitizing dose of allergen in this response/nonresponse paradigm, sensitizing BALB/c mice with 5 ng-2 microg of OVA-alum and assessing their responses to repeated OVA aerosol challenge. Mice sensitized with < or = 25 ng of OVA-alum did not develop atopic antibodies, airway hyperresponsiveness (AHR), eosinophilia, or pulmonary Th2 responses, but the 25-ng group animals did develop significant IgA responses. The mice sensitized with 100 ng of OVA-alum developed AHR in the absence of detectable allergic disease, while the mice sensitized with 250 ng-2 microg of OVA/alum developed full-spectrum allergic disease (i.e., eosinophilia, IgE, IgG1, pulmonary Th2 cytokine responses, and AHR). These data indicate that limiting doses of allergen can differentially induce IgA or AHR in the absence of atopic disease in mice. 相似文献
993.
T W Mitchell J Nissanov L Y Han E J Mufson J A Schneider E J Cochran D A Bennett V M Lee J Q Trojanowski S E Arnold 《The journal of histochemistry and cytochemistry》2000,48(12):1627-1638
Pathological alterations in dendrites and axons (i.e., neuritic pathologies) occur in the normal aging brain as well as in brains from elders with mild cognitive impairment and neurodegenerative dementia. These alterations may correlate with clinical measures of cognitive abilities, but the contribution of neuropil threads (NTs), which constitute 85-90% of cortical tau pathology, has not been clear because of the lack of quantitative methodologies. We combined quantitative fractionation and image analysis to devise a strategy for measuring the burden of tau-rich NTs in the entorhinal and perirhinal cortex of brains from elders with and without cognitive impairment, including dementia due to Alzheimer's disease (AD). On the basis of data presented here using this novel strategy, we conclude that this quantitative imaging technique will facilitate efforts to determine the behavioral correlations of neuritic lesions in AD and other brain disorders. 相似文献
994.
995.
Predation on urchins by migratory shorebirds was investigated during tidal exposure of the reef flat at Galeta, Panama. Avian predators, primarily ruddy turnstones Arenaria interpres (Linnaeus) reduced the patchiness of Echinometra lucunter (Linnaeus), the most abundant urchin on the reef flat. No mortality of E. lucunter occurred in quadrats protected from avian predation. No mortality occurred when urchin crowding was increased experimentally in protected areas. Stress-induced mortality could not be determined from the condition of tests alone, since turnstones were capable of removing lantern and internal organs without damage to the test. The importance of shorebird predation in reef communities during aerial exposure can be hard to detect because mortality can occur during brief periods, at night, and without damage to urchin tests. 相似文献
996.
Molecular phylogenetic analyses of mullets (Mugilidae, Mugiliformes) based on two mitochondrial genes 总被引:1,自引:0,他引:1
E. Fraga H. Schneider M. Nirchio E. Santa-Brigida L. F. Rodrigues-Filho I. Sampaio 《Zeitschrift fur angewandte Ichthyologie》2007,23(5):598-604
Molecular phylogenetic studies are very scarce for the Mugilidae family; the present analysis using DNA sequences of the mitochondrial 16S rRNA and cytochrome b genes is the first study involving Brazilian mugilids. The results corroborate the monophyly of Mugil and are elucidative for the taxonomy of Brazilian mugilids. Mugil curema is clearly divided into two genetically distinct taxa, M. curema type I being closer related to Mugil hospes and the true M. curema (type II) grouping significantly with M. incilis. The results also suggest that Mugil liza and Mugil platanus should be treated as a single species or even populations of Mugil cephalus. 相似文献
997.
Uwe Schneider Anja Fiedler Mario Liehr Christiane K?hler Ekkehard Schleussner 《Biomedizinische Technik》2006,51(4):248-250
Intrauterine growth restriction (IUGR) remains a major problem in perinatal medicine because of the variety of its underlying causes and the prediction of its outcome. Characteristics of heartbeat interval patterns are associated with neuro-vegetative and humoral regulatory processes. Fetal magnetocardiography allows non-invasive assessment of these processes with high precision throughout the second half of gestation. The aim of our study was the analysis of linear and non-linear parameters of fetal heart rate fluctuations to distinguish between IUGR fetuses and a cohort of normal subjects, both pre-selected from heart-rate traces representing a quiet state of activity in the third trimester of gestation. 相似文献
998.
Susheel P Patil Hartmut Schneider Jason J Marx Elizabeth Gladmon Alan R Schwartz Philip L Smith 《Journal of applied physiology》2007,102(2):547-556
Obstructive sleep apnea is caused by pharyngeal occlusion due to alterations in upper airway mechanical properties and/or disturbances in neuromuscular control. The objective of the study was to determine the relative contribution of mechanical loads and dynamic neuromuscular responses to pharyngeal collapse during sleep. Sixteen obstructive sleep apnea patients and sixteen normal subjects were matched on age, sex, and body mass index. Pharyngeal collapsibility, defined by the critical pressure, was measured during sleep. The critical pressure was partitioned between its passive mechanical properties (passive critical pressure) and active dynamic responses to upper airway obstruction (active critical pressure). Compared with normal subjects, sleep apnea patients demonstrated elevated mechanical loads as demonstrated by higher passive critical pressures [-0.05 (SD 2.4) vs. -4.5 cmH2O (SD 3.0), P = 0.0003]. Dynamic responses were depressed in sleep apnea patients, as suggested by failure to lower their active critical pressures [-1.6 (SD 3.5) vs. -11.1 cmH2O (SD 5.3), P < 0.0001] in response to upper airway obstruction. Moreover, elevated mechanical loads placed some normal individuals at risk for sleep apnea. In this subset, dynamic responses to upper airway obstruction compensated for mechanical loads and maintained airway patency by lowering the active critical pressure. The present study suggests that increased mechanical loads and blunted neuromuscular responses are both required for the development of obstructive sleep apnea. 相似文献
999.
Three species of marine algae are reported from the Bermuda islands for the first time, Avrainvillea sylvearleae D. S. Littler et Littler, Discosporangium mesarthrocarpum (Menegh.) Hauck, and Peyssonnelia valentinii Yonesh. et Boudour. The presence of Avrainvillea sylvearleae in Bermuda prompted a taxonomic reinvestigation of North Carolina specimens attributed recently to that taxon, and we find them better placed in A. longicaulis f. laxa D. S. Littler et Littler. The report of the eastern Atlantic/Mediterranean Discosporangium mesarthrocarpum is the first from the western Atlantic Ocean and joins only 12 other amphi-Atlantic species with strictly warm-temperate zone distributions. Peyssonnelia valentinii is discovered for the first time outside of Brazil. 相似文献
1000.
Targeted alteration of the substrate specificity of peptide synthetases by rational module swapping 总被引:7,自引:0,他引:7
Analysis of the primary structure of peptide synthetases involved in the non-ribosomal synthesis of peptide antibiotics has
revealed a highly conserved and ordered modular arrangement. A module contains at least two domains, involved in ATP-dependent
substrate activation and thioester formation. The occurrence and arrangement of these functional building blocks is associated
with the number and order of the amino acids incorporated in the peptide product. In this study, we present data on the targeted
exchange of the leucine-activating module within the three-module surfactin synthetase 1 (SrfA-A) of Bacillus subtilis. This was achieved by engineering several hybrid srfA-A genes, which were introduced into the surfactin biosynthesis operon by in vivo recombination. We examined the hybrid genes
for expression and investigated the enzymatic activities of the resulting recombinant peptide synthetases. For the first time,
we demonstrate directly that an individual minimal module, of bacterial or fungal origin, confers its amino acid-specific
activity on a multi-modular peptide synthetase. Furthermore, it is shown that directed incorporation of ornithine at the second
position of the peptide chain induces a global alteration in the conformation of surfactin and may result in premature cyclization
or a branched cyclic structure.
Received: 10 July 1997 / Accepted: 11 September 1997 相似文献