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91.
92.
Bodvin Torjan Indergaard Mentz Norgaard Erik Jensen Arne Skaar Arne 《Hydrobiologia》1996,335(1):83-86
A method has been developed for the determination of H2S and FeS in sediments. FeS is converted into H2S which is flushed from the samples directly into an excess of chlorine bleach, NaC1O or KClO with some Zn2+ added. Either the excess can be titrated back potentiometrically with As2O3, or the sulphate formed can be measured colorimetrically. The precision is primarily controlled by the homogeneity of the
sediment suspensions and can be better than 99%. 相似文献
93.
Molecular analysis of a beta-lactam resistance gene encoded within the cephamycin gene cluster of Streptomyces clavuligerus. 下载免费PDF全文
A Streptomyces clavuligerus gene (designated pcbR) which is located immediately downstream from the gene encoding isopenicillin N synthase in the cephamycin gene cluster was characterized. Nucleotide sequence analysis and database searching of PcbR identified a significant similarity between PcbR and proteins belonging to the family of high-molecular-weight group B penicillin-binding proteins (PBPs). Eight of nine boxes (motifs) conserved within this family of proteins are present in the PcbR protein sequence in the same order and with approximately the same spacing between them. When a mutant disrupted in pcbR was constructed by gene replacement, the resulting pcbR mutant exhibited a significant decrease in its resistance to benzylpenicillin and cephalosporins, indicating that pcbR is involved in beta-lactam resistance in this organism. Western blot (immunoblot) analysis of S. clavuligerus cell membranes using PcbR-specific antibodies suggested that PcbR is a membrane protein. PcbR was also present in cell membranes when expressed in Escherichia coli and was able to bind radioactive penicillin in a PBP assay, suggesting that PcbR is a PBP. When genomic DNAs from several actinomycetes were probed with pcbR, hybridization was observed to some but not all beta-lactam-producing actinomycetes. 相似文献
94.
Lisa M. Vogler Sumner W. Jones Glen E. Jensen R. Gary Brewer Karen J. Brewer 《Inorganica chimica acta》1996,250(1-2):155-162
A number of osmium and ruthenium complexes of the tridentate ligands 2,2′:6′,2″-terpyridine (tpy) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tpp) have been prepared and characterized by our laboratory. All these complexes possess metal based oxidations and ligand based reductions localized on each polyazine ligand. Polymetallic complexes bridged by the tpp ligand exhibit two sequential tpp based reductions prior to the reduction of other polyazine ligands in these complexes. The spectroscopy of these complexes is dominated by ligand based π-π* transitions in the ultraviolet and MLCT (metal-to-ligand charge transfer) bands terminating on each polyzine ligand in the visible. For the complexes reported herein the lowest lying optical transitionis a M → BL CT band. For most of the complexes reported, occupation of this excited state gives rise to an observable emission at room temperature. For ruthenium complexes of these tridentate ligands, the presence of a low-lying LF state shortens the excited state lifetimes of these chromophores. This gives rise to ruthenium complexes that display shorter excited state lifetimes than the analogous osmium based systems. Incorporation of tpp based chromophores into polymetallic frameworks leads to the production of bimetallic species with long-lived excited states, 100 ns at room temperature. This makes these chromophores good candidates for the development of stereochemically defined supramolecular complexes. It is possible to measure an electrochemical HOMO-LUMO energy gap and a correlation between this electrochemically measured energy gap and the spectroscopic energy associated with this HOMO→LUMO transition are reported herein (HOMO== highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital). 相似文献
95.
A novel type of DNA-binding protein interacts with a conserved sequence in an early nodulin ENOD12 promoter 总被引:3,自引:0,他引:3
96.
Grain yield, symbiotic N2 fixation and interspecific competition for inorganic N in pea-barley intercrops 总被引:4,自引:0,他引:4
Erik Steen Jensen 《Plant and Soil》1996,182(1):25-38
The effect of mixed intercropping of field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.), compared to monocrop cultivation, on the yield and crop-N dynamics was studied in a 4-yr field experiment using 15N-isotope dilution technique. Crops were grown with or without the supply of 5 g 15N-labeled N m-2. The effect of intercropping on the dry matter and N yields, competition for inorganic N among the intercrop components, symbiotic fixation in pea and N transfer from pea to barley were determined. As an average of four years the grain yields were similar in monocropped pea, monocropped and fertilized barley and the intercrop without N fertilizer supply. Nitrogen fertilization did not influence the intercrop yield, but decreased the proportion of pea in the yield. Relative yield totals (RYT) showed that the environmental sources for plant growth were used from 12 to 31% more efficiently by the intercrop than by the monocrops, and N fertilization decreased RYT-values. Intercrop yields were less stable than monocrop barley yields, but more stable than the yield of monocropped pea. Barley competed strongly for soil and fertilizer N in the intercrop, and was up to 30 times more competitive than pea for inorganic N. Consequently, barley obtained a more than proportionate share of the inorganic N in the intercrop. At maturity the total recovery of fertilizer N was not significantly different between crops, averaging 65% of the supplied N. The fertilizer N recovered in pea constituted only 9% of total fertilizer-N recovery in the intercrop. The amount of symbiotic N2 fixation in the intercrop was less than expected from its composition and the fixation in monocrop. This indicates that the competition from barley had a negative effect on the fixation, perhaps via shading. At maturity, the average amount of N2 fixation was 17.7 g N m-2 in the monocrop and 5.1 g N m-2 in the intercropped pea. A higher proportion of total N in pea was derived from N2 fixation in the intercrop than in the monocrop, on average 82% and 62%, respectively. The 15N enrichment of intercropped barley tended to be slightly lower than of monocropped barley, although not significantly. Consequently, there was no evidence for pea N being transferred to barley. The intercropping advantage in the pea-barley intercrop is mainly due to the complimentary use of soil inorganic and atmospheric N sources by the intercrop components, resulting in reduced competition for inorganic N, rather than a facilitative effect, in which symbiotically fixed N2 is made available to barley.Abbreviations MC
monocrop
- IC
intercrop
- PMC
pea monocrop
- BMC
barley monocrop
- PIC
pea in intercrop
- BIC
barley in intercrop 相似文献
97.
Drought signal transduction in plants 总被引:5,自引:0,他引:5
Anders B. Jensen Peter K. Busk Mercé Figueras M. Mar Albà Giovanna Peracchia Ramon Messeguer Adela Goday Montserrat Pagès 《Plant Growth Regulation》1996,20(2):105-110
Water deficit is one of the most common environmental limitations of crop productivity by affecting growth through alterations in metabolism and gene expression. The mechanisms involved in drought perception and signal transduction pathways are poorly understood. The participation of the plant hormone abscisic acid (ABA) has been well established. ABA levels increase when there are changes in the environment that result in cellular dehydration. Different approaches have been taken to understanding the molecular responses to desiccation and how ABA regulates gene expression. Recent efforts have identified particular topics of importance in the dissection of the signal transduction pathway which are summarized as follows: physiological approaches: identification of signalling molecules. Genetic approaches: the use of mutants, and Molecular approaches: promoter analysis. 相似文献
98.
Analysis of functional domain organization in DNA topoisomerase II from humans and Saccharomyces cerevisiae. 总被引:4,自引:0,他引:4 下载免费PDF全文
S Jensen A H Andersen E Kjeldsen H Biersack E H Olsen T B Andersen O Westergaard B K Jakobsen 《Molecular and cellular biology》1996,16(7):3866-3877
The functional domain structure of human DNA topoisomerase IIalpha and Saccharomyces cerevisiae DNA topoisomerase II was studied by investigating the abilities of insertion and deletion mutant enzymes to support mitotic growth and catalyze transitions in DNA topology in vitro. Alignment of the human topoisomerase IIalpha and S. cerevisiae topoisomerase II sequences defined 13 conserved regions separated by less conserved or differently spaced sequences. The spatial tolerance of the spacer regions was addressed by insertion of linkers. The importance of the conserved regions was assessed through deletion of individual domains. We found that the exact spacing between most of the conserved domains is noncritical, as insertions in the spacer regions were tolerated with no influence on complementation ability. All conserved domains, however, are essential for sustained mitotic growth of S. cerevisiae and for enzymatic activity in vitro. A series of topoisomerase II carboxy-terminal truncations were investigated with respect to the ability to support viability, cellular localization, and enzymatic properties. The analysis showed that the divergent carboxy-terminal region of human topoisomerase IIalpha is dispensable for catalytic activity but contains elements that specifically locate the protein to the nucleus. 相似文献
99.
Tenshuk A. Kadima Susan E. Jensen Michael A. Pickard 《Journal of industrial microbiology & biotechnology》1995,14(1):35-40
Summary -(l--Aminoadipyl)-l-cysteinyl-d-valine (ACV)-synthetase fromStreptomyces clavuligerus was studied under conditions that enabled the reuse of the enzyme. Coupling of ACV-synthetase to DEAE-Trisacryl and aminopropyl-glass resulted in an immobilized enzyme product of little or no catalytic activity. However, an enzyme reactor was designed by physical confinement of partially-purified ACV-synthetase in an ultrafiltration cell. This system was stimulated by phosphoenolpyruvate at lower concentrations of ATP, an effect not observed with purified enzyme. Up to 30% conversion of the limiting substrate, cysteine, to ACV occurred under semi-continuous conditions. Reaction products were investigated as potential inhibitors: AMP was the most inhibitory, but only when used at concentrations in excess of those produced in reaction mixtures. Under a nitrogen atmosphere, both product and enzyme stabilities were greatly improved and the enzyme retained 45–46% of its initial activity after five uses at room temperature during a 24-h period. Extrapolations based on these data suggest that 1.3 g partially purified enzyme (0.13 U g–1) would be capable of producing 411 mg of ACV in a 1-L reaction mixture in this period. 相似文献
100.
Staphylococcal enterotoxins (SE’s) are a group of small exoproteins produced by some strains of Staphylococcus aureus. The SE’s, designated A to E according to their antigenic specificities, are important causes of food poisoning worldwide. Milk and dairy products are frequently associated with S. aureus enter-otoxin food poisoning, and it is supposed that infected milk from mastitic animals constitute the main source of enterotoxigenic S. aureus of animal origin (Bryon 1983, Gilmour & Harvey 1990, Bergdoll 1989). Indeed, S. aureus is the most common cause of bovine mastitis worldwide, and if mastitis strains produce SE this makes up an enormous reservoir of potential enterotoxin producers. The production of SE by S. aureus isolated from bovine mastitis have been investigated in several countries (Matsunaga et al. 1993, Kenny et al. 1993, Olson et al 1970, Orden et al. 1992, Olsvik et al. 1981, Adekeye 1980, Garcia et al. 1980, Abbar 1986, Harvey & Gilmour 1985). Since no studies have been performed on the prevalence of enterotoxigenic strains of S. aureus isolated from bovine mastitis in Denmark, a well characterized collection of S. aureus (Aarestrup et al. 1995) was investigated with respect to this property. 相似文献