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851.
852.
This study evaluated diazotrophic bacterial diversity of soils from four different sites in South and North America. Approximately one hundred and thirty-nine thousand partial sequences of the small subunit of the bacterial ribosomal RNA gene generated for a previous study were used for this work. Sequences that presented at least 90% similarity with known diazotrophic organisms were pulled from the original dataset and a new library containing 14,842 sequences from nitrogen-fixing bacteria were analysed. The number of sequences and the abundance of identifiable/cultivable diazotrophic genera were used for the calculation of the Shannon–Weaver diversity index and Evenness. All soils exhibited similar diazotrophic diversity, illustrating the great amount of similarity found between randomly chosen soils. Out of 81 diazotrophic genera, 45 were found in common in the four soils tested irrespective of the localization or cultivation. The degree of dominance of these common genera within their communties differed widely between soils. Sixteen types were found in only one sample.  相似文献   
853.
Epidemiological studies of paracoccidioidomycosis have been based on surveys achieved with intradermal tests, and paracoccidioidin is the most common antigen used in most cases. The glycoprotein of 43-kDa (gp43) has been used in intradermal tests. It is the most antigenic component of Paracoccidioides brasiliensis, and it provides greater specificity to evaluate infection for this fungus. In this study, the prevalence of P. brasiliensis infection was estimated with intradermal tests involving gp43 for 695 people in rural Central-West Brazil. The infection rate was 45.8 % (95 % CI = 42.1–49.5), and the average age of those infected was 45.8 ± 18.2 years. The prevalence did not show gender-based differences but increased with age. The results demonstrate the importance of P. brasiliensis infection in rural settlements and the early exposure of children in the region to the fungus. Despite the high antigenicity and specificity of gp43, its usage must be standardized, so that epidemiological surveys will be comparable and more accurately reflect P. brasiliensis infection in endemic areas.  相似文献   
854.
855.
Endo-oligopeptidase A, highly purified from the cytosol fraction of bovine brain by immunoaffinity chromatography, has been characterised as a thiol endopeptidase. This enzyme, known to hydrolyse the Phe5-Ser6 bond of bradykinin and the Arg8-Arg9 bond of neurotensin has been shown to produce, by a single cleavage, [Leu]enkephalin or [Met]enkephalin from small enkephalin-containing peptides. Enkephalin formation could be inhibited in a concentration dependent manner by the alternative substrate bradykinin. The optimal substrate size was found to be 8-13 amino acids, with enkephalin the only product released from precursors in which this sequence is immediately followed by a pair of basic residues. However, the specificity constants (kcat/Km) obtained for endo-oligopeptidase A hydrolysis of bradykinin, neurotensin and dynorphin B are of the same order. Taken together, these results indicate that the substrate amino acid sequence is not the only factor determining the cleavage site of this enzyme. Finally, endo-oligopeptidase A and metalloendopeptidase EC 3.4.24.15 are two different enzymes. The latter is not able to liberate enkephalins from metorphamide and dynorphin.  相似文献   
856.
857.
858.
Cyclodextrins in the treatment of a mouse model of Niemann-Pick C disease.   总被引:5,自引:0,他引:5  
Niemann-Pick type C (NPC) is a neurodegenerative disorder characterized by greatly altered somatic cholesterol metabolism. The NPC1 gene has recently been cloned and shown to have sequence homology to other sterol-sensing proteins. We have used a mouse model with a disrupted npc1 gene to study the effects of the cholesterol-mobilizing compound, 2-hydroxypropyl-beta-cyclodextrins (HPBCD), on the clinical course of this disorder. Treatment with two HPBCDs, with varying levels of 2-hydroxypropyl substitution, had effects in delaying neurological symptoms and in decreasing liver cholesterol storage while a third HPBCD was without effect. The ameliorating effect was not improved by longer exposure times (commencement of exposure in utero), however, it is not known if there is transplacental transfer of HPBCDs. The combination of HPBCD with probucol or nifedipine (which have previously been shown to lower liver cholesterol in this animal model) markedly decreased liver storage of unesterified cholesterol without altering the depressed levels of esterified cholesterol. The slight effects of the HPBCDs on neurological symptoms may be partially due to their apparent non-permeation of the blood-brain barrier (BBB). This non-permeation was assayed with radioactive tracers and was also present in the mdr1a knockout mice which have greatly increased BBB permeability for many drugs. Intrathecal delivery of HPBCD by an Alzet osmotic minipump did not improve its efficacy in ameliorating neurological symptoms.  相似文献   
859.

Background  

Leishmania (Leishmania) amazonensis infection in man results in a clinical spectrum of disease manifestations ranging from cutaneous to mucosal or visceral involvement. In the present study, we have investigated the genetic variability of 18 L. amazonensis strains isolated in northeastern Brazil from patients with different clinical manifestations of leishmaniasis. Parasite DNA was analyzed by sequencing of the ITS flanking the 5.8 S subunit of the ribosomal RNA genes, by RAPD and SSR-PCR and by PFGE followed by hybridization with gene-specific probes.  相似文献   
860.
During foraging, worker ants are known for making use of many information sources to guide themselves in external environments, especially individual (memory) and social (trail pheromone) information. Both kinds of information act in a synergic way, keeping the foraging process efficient and organized. However, when social and individual information is conflicting face a trail bifurcation, it is necessary to establish a hierarchical order so prioritizing one of them. This study aims to verify which information (social or individual) is prioritized by Acromyrmex subterraneus workers when facing a bifurcation in a Y-trail system. Only one branch of the Y-trail leads to food resource and it had a section covered by filter paper where trail pheromone was deposited by workers. Pheromone deposition was here estimated by worker flow. After an individually marked forager (target-worker) made 1, 3 or 5 trips to the food resource, the filter paper was transferred to the branch which did not lead to the food. The time spent by target workers on branch selection and their right choice (branch with food) frequency were registered. Regardless of the target worker's previous trips to the resource, right choice frequency stood over 70%. In addition, the number of previous trips did not influence the time spent on decision making. However, the higher the flow of workers, the longer the time spent on decision making. By simulating a situation with conflicting information, it was possible to verify that a hierarchical order is established by A. subterraneus, which prioritized individual information (memory).  相似文献   
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