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S-containing amino acids can lead to two types of local NH···S interactions which bridge backbone NH sites to the side chain to form either intra- or inter-residue H-bonds. The present work reports on the conformational preferences of S-methyl-l-cysteine, Cys(Me), using a variety of investigating tools, ranging from quantum chemistry simulations, gas-phase UV and IR laser spectroscopy, and solution state IR and NMR spectroscopies, on model compounds comprising one or two Cys(Me) residues. We demonstrate that in gas phase and in low polarity solution, the C- and N-capped model compound for one Cys(Me) residue adopts a preferred C5–C6γ conformation which combines an intra-residue N–H···O=C backbone interaction (C5) and an inter-residue N–H···S interaction implicating the side-chain sulfur atom (C6γ). In contrast, the dominant conformation of the C- and N-capped model compound featuring two consecutive Cys(Me) residues is a regular type I β-turn. This structure is incompatible with concomitant C6γ interactions, which are no longer in evidence. Instead, C5γ interactions occur, that are fully consistent with the turn geometry and additionally stabilize the structure. Comparison with the thietane amino acid Attc, which exhibits a rigid cyclic side chain, pinpoints the significance of side chain flexibility for the specific conformational behavior of Cys(Me).

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We investigate how perturbations that induce mortality transform original spatial patterns in plant communities into binary spatial patterns of survivors and perished individuals. By means of computer simulation, we analyse effects of average mortality, interspecific variation of mortality around the mean, spatial distribution of the species (clumping degree), and species richness. Gap spatial pattern is quantified by four spatial indices or landscape metrics (gap area, density, shape and coherence). In single‐species communities, the emerging gap patterns are subject to critical phenomena: opportunities for colonizers to establish increase with mortality, but more rapidly at specific mortality thresholds. In multi‐species communities, neither species richness nor interspecific variation of mortality influences gap spatial pattern when community assembly is random. Colonization opportunities would therefore not be affected by local species extinction in such a system, nor by the presence of species with divergent sensitivities to perturbation. In a community that is highly spatially aggregated, increases in interspecific mortality variation shift the pattern towards fewer gaps that are larger and more isodiametric, which suggests increased establishment chances for colonizers. Similar changes are induced in communities characterized by large interspecific mortality differences if clumping degree is increased. Loss of species richness only modifies gap spatial pattern to a substantial extent if mortality variation is high: in this case, depauperate communities exhibit a wider variety of colonization opportunities (more gaps which are on average smaller, but the largest gap is larger) than species‐richer ones. These findings may explain the contrast between the negative diversity‐invasibility relationship often found in small‐scale experimental studies and the positive diversity‐invasibility relationship found in observational studies at larger scale. They also demonstrate that the pre‐disturbance spatial structure of a community significantly affects colonization opportunities for alien species, and is therefore a likely determinant of the trajectory of secondary succession following perturbation.  相似文献   
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A total of 1347 weaned lambs from eight genotypes were tested over five consecutive years: Romanov (ROM) and Lacaune (LAC) pure breeds, the two F1 crossbreeds (RL and LR) and the offspring of ewes from these four genotypes sired with Berrichon-du-Cher rams (BCF). The lambs were individually exposed to three challenging tests involving novelty, human contact and social isolation. Ten synthetic variables were used to express social reactivity (i.e., active vs. passive strategy), exploratory activity and reactivity to humans. BCF crossbreds were more active (i.e., high bleats, locomotion and attempts to escape) than purebreds and F1. In contrast, ROM expressed more passive responses (i.e., low bleats and vigilance postures) than LAC and BCF crossbreds. In addition, ROM approached a motionless human less and had longer flight distances to an approaching human than did LAC and BCF crossbreds. When restrained, ROM, and to a lesser extent B×ROM and B×LR, avoided human contact more than did LAC, RL and B×LAC. Most of these differences were explained by direct additive genetic effects while maternal influences or heterosis effects were rarely significant. The highest heritability was for high bleats (h2 = 0.48). Females were more active and avoided human contact more than did males.  相似文献   
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We have developed a personal-computer-based water quality analysis system for river basins. The system estimates potential N outflow by model and calculates actual N outflow from monitoring data. For the former it uses the potential load factor method to estimate annual nitrogen load from various sources and runoff potential from each area of land in a basin. For the latter it analyzes water quality monitoring data in relation to meteorological data. We used the system to analyze N outflow in basins around Lake Kasumigaura and the Yahagi River in central Honshu, Japan. The land around Lake Kasumigaura is rather flat, and about 25% is periodically flooded for rice and lotus cultivation. The land around the Yahagi River is mountainous, and much less land is flooded. In the Yahagi River basin the actual N outflow agreed closely with the potential. However, the actual N outflow in the basin around Lake Kasumigaura was much less than the potential, suggesting that a large part of the N load is denitrified in flooded soils. This further indicates that a sequence of different land uses including flooded rice fields is an important factor determining N outflow in basins in Japan. On the basis of the above analyses, we incorporated a denitrification model into the system that enables us to estimate N balance in a designated basin; this system may be helpful in the formulation of scenarios of land use and soil management for improving water quality.  相似文献   
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The effects of rose-flower extract on antioxidant enzymes were studied. The activities of catalase (CAT) and glutathione peroxidase (GPx) in 9-month-old senescence-accelerated mice (SAM mice) were lower than those in 6-month-old SAM mice. Therefore, 9-month-old SAM mice were the most appropriate targets for treatment with the rose-flower extract. The activities of CAT and GPx in SAM mice treated with rose-flower extract showed a marked increase in whole blood and liver. At the same time, the gene-expression level of CAT and GPx was upregulated in the liver, while malondialdehyde content in liver and brain decreased. Male SAM mice were more sensitive than female SAM mice. The mean and the longest lifespan of SAM mice were longer after treatment with rose-flower extract.  相似文献   
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