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排序方式: 共有173条查询结果,搜索用时 15 毫秒
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Ethel Dukes 《BMJ (Clinical research ed.)》1938,2(4047):213-215
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R G Painter R Dukes J Sullivan R Carter E G Erd?s A R Johnson 《The Journal of biological chemistry》1988,263(19):9456-9461
Intact human neutrophils hydrolyzed N-formyl-Met-Leu-[3H]Phe (fMLP) and released Leu-[3H]Phe, cleaving 45-50% of the peptide within 20 min at 37 degrees C. The dipeptide after its release was then hydrolyzed to free amino acids by a dipeptidase (EC 3.4.13.11). This activity, present in plasma membrane-enriched fractions of neutrophil lysates, was also inhibited over 90% by phosphoramidon, an inhibitor of neutral endopeptidase (NEP, EC 3.4.24.11). Dithiothreitol and EDTA inhibited the activity to a comparable degree, suggesting the requirement for a heavy metal cofactor. Bestatin and amastatin, inhibitors of aminopeptidases (but not human kidney NEP), did not inhibit the rate of fMLP degradation but prevented the production of free phenylalanine and enhanced the accumulation of Leu-Phe. Of other inhibitors, alpha 1-antitrypsin and alpha 2-macroglobulin slightly enhanced the rate of fMLP hydrolysis by neutrophils, and others tested were ineffective. Rabbit antiserum to homogeneous human kidney NEP reacted specifically with a 100-kDa protein present in sodium dodecyl sulfate-solubilized neutrophils. The Mr of this protein was slightly larger than that of the kidney enzyme in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The antiserum incubated with intact cells specifically inhibited the degradation of fMLP over 70%. First, we confirm that NEP present on the plasma membrane cleaves fMLP at the Met-Leu bond; then the dipeptide Leu-Phe is cleaved by a dipeptidase. Finally, inhibition of NEP completely blocks fMLP-mediated chemotaxis. Thus, the enzyme may play an important role in modulating chemotactic responses. 相似文献
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J C Waterton D Miller J S Morrell M Dukes C D West P F Wadsworth 《Laboratory animals》1992,26(1):59-64
A case of spontaneous endometriosis was diagnosed in the pigtailed macaque (Macaca nemestrina nemestrina) with the aid of high-field (2.35 T), T2-weighted (TE50), C1H2-suppressed, oblique nuclear magnetic resonance imaging (MRI). Postmortem histology was obtained. A variety of endometriotic lesions was seen with MRI, including extrauterine hyperintense apparently cystic regions, extrauterine hypointense regions apparently associated with intracellular paramagnetic iron proteins, and an enlarged myometrium exhibiting adenomyosis foci. 相似文献
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V Z Pletnev I N Tsygannik Iu D Fonarev V T Ivanov D A Lengs P Grokhul'ski? V L Dukes 《Bioorganicheskaia khimiia》1992,18(6):794-801
The crystal structure of a valinomycin analogue, cyclo[-(D-Val-Hyi-Val-D-Hyi)3-]x(C60H102N6O18) crystallized with dioxane and water molecules, has been solved by X-ray direct methods. The conformation found is analogous to one established for free meso-valinomycin crystallized from other organic solvents. It is characterized by a centrosymmetric bracelet form, stabilized by six intramolecular 4----1 type hydrogen bonds between amide N-H and C = O groups. One water molecule is fixed asymmetrically by hydrogen bonds in the internal negatively charged cavity of the complexon. The meso-valinomycin molecule "bracelets" in the crystal form stacks alternatively with dioxane molecules. 相似文献
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Mechanisms underlying the impacts of exotic plant invasions 总被引:37,自引:0,他引:37
Levine JM Vilà M D'Antonio CM Dukes JS Grigulis K Lavorel S 《Proceedings. Biological sciences / The Royal Society》2003,270(1517):775-781
Although the impacts of exotic plant invasions on community structure and ecosystem processes are well appreciated, the pathways or mechanisms that underlie these impacts are poorly understood. Better exploration of these processes is essential to understanding why exotic plants impact only certain systems, and why only some invaders have large impacts. Here, we review over 150 studies to evaluate the mechanisms underlying the impacts of exotic plant invasions on plant and animal community structure, nutrient cycling, hydrology and fire regimes. We find that, while numerous studies have examined the impacts of invasions on plant diversity and composition, less than 5% test whether these effects arise through competition, allelopathy, alteration of ecosystem variables or other processes. Nonetheless, competition was often hypothesized, and nearly all studies competing native and alien plants against each other found strong competitive effects of exotic species. In contrast to studies of the impacts on plant community structure and higher trophic levels, research examining impacts on nitrogen cycling, hydrology and fire regimes is generally highly mechanistic, often motivated by specific invader traits. We encourage future studies that link impacts on community structure to ecosystem processes, and relate the controls over invasibility to the controls over impact. 相似文献