104,957 research outputs found
Plant biochemistry of xenobiotics: Isolation and characterization of a soybean <em>O</em>-glucosyltransferase of DDT metabolism.
No full textThe insecticide DDT is metabolized in soybean and wheat cell cultures to the acylglucoside of 2,2-bis-(4-chlorophenyl)-acetic acid (DDA) (M. Arjmand and H. Sandermann, 1985, Pesticide Biochem. Physiol. 23, 389-397). An enzyme catalyzing the conjugation reaction has been highly purified from the soluble enzyme fraction of cultured soybean cells. After the initial ammonium sulfate fractionation, quercetin and pentachlorophenol were preferentially glucosylated. In the course of 367-fold purification, DDA became the preferred substrate. The purified enzyme was unstable. A molecular weight of ~50 kDa was estimated for the native enzyme (gel permeation chromatography) as well as the denatured protein (sodium dodecyl sulfate-gel electrophoresis). The isoelectric point for the enzyme was near pH 4.9. Apparent K(m) values of about 170 μM were determined for UDP-glucose as well as DDA. The maximal velocity was 257 μkat/kg protein, corresponding to a conjugation capacity of 855 μg DDA/h/g fresh weight of cells
Role of Ozone in Forest Decline on Wank Mountain (Alps)
No full textFrom crown-thinning of spruce it has been estimated that one-third of the mountain forests in the Bavarian Alps are severely damaged (Kennel 1990). Photo-oxidants transported above inversion layers have been thought to be responsible for the damage observed in these forests (Seiler 1988; Fabian 1990). As 03 is a key product of photo-oxidative chain reactions in the troposphere and tropospheric 03 concentrations change with increasing altitude, 03 has been implicated as the central cause of this forest decline (Seiler 1988). Climatic stress, nutrient deficiencies, forest management and genetic properties of the trees have also been considered as predisposing or triggering factors (Rennenberg and Reuther 1991). The general objective of the studies performed in the Bavarian Alps at the Wank mountain research site has been to test this hypothesis using an interdisciplinary approach. To meet this objective, scientists working in forestry, meteorology, air chemistry, tree physiology, soil sciences, ecology and taxonomy participated in these studies which lasted for almost a decade. The individual objectives of the research performed were (1) to characterize the particular stand, especially the atmospheric and pedospheric environment, and to assess the vitality and the nutritional status of the trees and (2) to identify and characterize those physiological parameters that exhibit changes with altitude similar to those associated with 03 (Rennenberg and Reuther 1991). In this chapter, the results obtained in the studies at the Wank mountain research site are summarized. In addition, the question is addressed as to whether altitude-dependent changes of the parameters studied provide evidence for stress to the trees, can be connected with the damage observed, and are the result of O3 exposure
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Forest decline and ozone: a comparison of controlled chamber and field experiments/ Edit.: Sandermann
No full textxxi, 480 hal.: ill.; 23 cm
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