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Biosynthesis of the metallocenter in the active site of the [NiFe] hydrogenase enzyme requires the accessory protein HypB, which is a metal-binding GTPase. In this study, the interplay between the individual activities of Escherichia coli HypB was examined. The full-length protein undergoes nucleotide-responsive dimerization that is disrupted upon mutation of L242 and L246 to alanine. This mutant HypB is monomeric under all of the conditions investigated but the inability of L242A/L246A HypB to dimerize does not abolish its GTPase activity and the monomeric protein has metal-binding behavior similar to that of wild-type HypB. Furthermore, expression of L242A/L246A HypB in vivo results in hydrogenase activity that is approximately half of the activity produced by the wild-type control, suggesting that dimerization of HypB does not have a critical role in the hydrogenase maturation pathway. In contrast, the GTPase activity of HypB is modulated by metal loading of the protein. These results provide insight into the role of HypB in hydrogenase biosynthesis.  相似文献   
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Satellite imagery as a tool for monitoring species diversity: an assessment   总被引:11,自引:1,他引:10  
1. A landscape of 5 × 5·5 km in the Karnataka region of the Western Ghats of India was mapped into seven landscape element types, using field identification of types as well as supervised and unsupervised classification of satellite imagery.
2. Plant communities distributed in these landscape element types were surveyed in the field using 246 quadrats of 10 × 10 m, in order to assess whether these types could be distinguished in terms of species composition. All angiosperms excluding grasses, which could not be identified accurately in the field, were recorded for this purpose.
3. Landscape element types identified in the field harboured significantly distinctive sets of species of flowering plants, and were also by and large distinctive in terms of their species richness.
4. Landscape element types could be identified accurately on the basis of supervised classification: the types thus demarcated harboured distinctive sets of flowering plants.
5. Landscape element types coupled to satellite imagery could then be used to organize a programme of monitoring biodiversity.
6. Unsupervised classification of satellite imagery did not permit classification of landscape element types with a high enough level of accuracy. In consequence, the demarcated landscape element types did not harbour significantly distinctive sets of species of flowering plants. Unsupervised classification is therefore not appropriate in a programme of monitoring biodiversity.  相似文献   
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This work presents a novel multivariate statistical algorithm, Decision Tree-PLS (DT-PLS), to improve the prediction and understanding of dynamic processes based on local partial least square regression (PLSR) models for characteristic process groups defined based on Decision Tree (DT) analysis. The DT-PLS algorithm is successfully applied to two different cell culture data sets, one obtained from bioreactors of 3.5 L lab scale and the other obtained from the 15 ml ambr microbioreactor system. Substantial improvement in the predictive capabilities of the model can be achieved based on the localization compared to the classical PLSR approach, which is implemented in the commercially available packages. Additionally, the differences in the model parameters of the local models suggest that the governing process variables vary for the different process regimes indicating the different states of the cell under different process conditions.  相似文献   
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In fast-changing tropical landscapes, effective strategies for conservation must incorporate information on ecosystems and species distribution with that on landscape change. A possible methodology for conservation prioritization is developed and illustrated using a 27.5 km2 tropical landscape in the Western Ghats hill chain of southern India. Vegetation types or ecosystems within the landscape are ranked based on the ecosystem services they might provide: number of endemic species harbored, species richness, contribution to carbon uptake, economic value of produce per ha and contribution to soil renewal. For a vegetation type, the weighted average of these ranks indicates its net conservation value. Weights thus provide a means of ascribing differential importance to an ecosystem service. Information on landscape change is also summarized by a matrix depicting the likelihood of transformations between vegetation types present in the landscape, projected 5 years into the future. For each transformation between two vegetation types, information on ecosystem service and dynamics is then integrated. Implications from the perspective of conservation are assessed as the product of transformation probability and the resultant gain/loss in conservation value. Strongly positive transformations are likely to result in positive impacts on conservation value, and occur without any additional conservation effort. Strongly negative transformations are likely to occur and have a strong negative impact on conservation value. Maximum conservation effort may be directed at halting or reversing these. This study thus describes a method for conservation prioritization, which integrates information on ecosystem function and services with ecosystem dynamics.  相似文献   
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