The positive-strangeness baryon resonance Θ+ is observed in photoproduction of the nK+K0s final state with the SAPHIR detector at the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in ...the nK+ invariant mass distribution with a 4.8σ confidence level. We find a mass MΘ+=1540±4±2 MeV and an upper limit of the width ΓΘ+<25 MeV at 90% c.l. The photoproduction cross section for K0Θ+ is in the order of 300 nb. From the absence of a signal in the pK+ invariant mass distribution in γp→pK+K− at the expected strength we conclude that the Θ+ must be isoscalar.
The application of flavin-dependent halogenases is hampered by their lack of stability under reaction conditions. However, first attempts to improve halogenase stability by error-prone PCR have ...resulted in mutants with higher temperature stability. To facilitate the screening for mutants with higher activity, a high-throughput assay was developed. Formation of cross-linked enzyme aggregates (CLEAs) of halogenases has increased halogenase lifetime by a factor of about 10, and CLEAs have been used to produce halogenated tryptophan in gram scale. Analyses of the substrate specificity of tryptophan halogenases have shown that they accept a much broader range of substrates than previously thought. The introduction of tryptophan halogenase genes into bacteria and plants led to the in vivo formation of peptides containing halogenated tryptophan or novel tryptophan-derived alkaloids, respectively. The halogen atoms in these compounds could be chemically exchanged against other substituents by cross-coupling reactions leading to novel compounds. Site-directed mutageneses have been used to modify the substrate specificity and the regioselectivity of flavin-dependent tryptophan halogenases. Since many flavin-dependent halogenases only accept protein-bound substrates, enzymatic and chemoenzymatic syntheses for protein-tethered substrates were developed, and the synthesized substrates were used in enzymatic halogenation reactions.
Low-energy photoproduction of $\omega$ -mesons Barth, J.; Braun, W.; Ernst, J. ...
The European physical journal. A, Hadrons and nuclei,
09/2003, Letnik:
18, Številka:
1
Journal Article
Pyrrolnitrin is a secondary metabolite of Pseudomonas and Burkholderia sp. strains with strong antifungal activity. Production of pyrrolnitrin has been correlated with the ability of some bacteria to ...control plant diseases caused by fungal pathogens, including the damping-off pathogen Rhizoctonia solani. Pseudomonas fluorescens BL915 has been reported to produce pyrrolnitrin and to be an effective biocontrol agent for this pathogen. We have isolated a 32-kb genomic DNA fragment from this strain that contains genes involved in the biosynthesis of pyrrolnitrin. Marker-exchange mutagenesis of this DNA with Tn5 revealed the presence of a 6.2-kb region that contains genes required for the synthesis of pyrrolnitrin. The nucleotide sequence of the 6.2-kb region was determined and found to contain a cluster of four genes that are required for the production of pyrrolnitrin. Deletion mutations in any of the four genes resulted in a pyrrolnitrin-nonproducing phenotype. The putative coding sequences of the four individual genes were cloned by PCR and fused to the tac promoter from Escherichia coli. In each case, the appropriate tac promoter-pyrrolnitrin gene fusion was shown to complement the pyrrolnitrin-negative phenotype of the corresponding deletion mutant. Transfer of the four gene cluster to E. coli resulted in the production of pyrrolnitrin by this organism, thereby demonstrating that the four genes are sufficient for the production of this metabolite and represent all of the genes required to encode the pathway for pyrrolnitrin biosynthesis
A large number of halogenated compounds is produced by chemical synthesis. Some of these compounds are very toxic and cause enormous problems to human health and to the environment. Investigations on ...the degradation of halocompounds by microorganisms have led to the detection of various dehalogenating enzymes catalyzing the removal of halogen atoms under aerobic and anaerobic conditions involving different mechanisms. On the other hand, more than 3500 halocompounds are known to be produced biologically, some of them in great amounts. Until 1997, only haloperoxidases were thought to be responsible for incorporation of halogen atoms into organic compounds. However, recent investigations into the biosynthesis of halogenated metabolites by bacteria have shown that a novel type of halogenating enzymes, FADH
2-dependent halogenases, are involved in biosyntheses of halogenated metabolites. In every gene cluster coding for the biosynthesis of a halogenated metabolite, isolated so far, one or several genes for FADH
2-dependent halogenases have been identified.
This research aims to apprehend: (1) the shape of tetrahedral chemistry education which is called the future of chemistry education, (2) comprehensive understanding of chemistry first-year students ...of Technische Universität Dresden according to the chemistry education's tetrahedral shape on mole concept subject matter. This research used quantitative and qualitative; paper and pencil test and interview. The former was conducted in the form of test containing objective test instrument. The results of this study are (1) learning based on tetrahedral shape of chemistry education put the chemical substance (macroscopic), symbolic representation (symbol), and its process (molecular) in the context of human beings (human element) by integrating content and context, without emphasis on one thing and weaken another, (2) first-year chemistry students of Technische Universität Dresden have comprehensively understood the mole concept associated with the context of everyday life, whereby students are able to find out macroscopic information from statements that are contextual to human life and then by using symbols and formulas are able to comprehend the molecular components as well as to interpret and analyse problems effectively.
Halometabolites are compounds that are commonly found in nature and they are produced by many different organisms. Whereas bromometabolites can mainly be found in the marine environment, ...chlorometabolites are predominately produced by terrestrial organisms; iodo- and fluorocompounds are only produced infrequently. The halogen atoms are incorporated into organic compounds by enzyme-catalyzed reactions with halide ions as the halogen source. For over 40 years haloperoxidases were thought to be responsible for the incorporation of halogen atoms into organic molecules. However, haloperoxidases lack substrate specificity and regioselectivity, and the connection of haloperoxidases with the in vivo formation of halometabolites has never been demonstrated. Recently, molecular genetic investigations showed that, at least in bacteria, a different class of halogenases is involved in halometabolite formation. These halogenases were found to require FADH2, which can be produced from FAD and NADH by unspecific flavin reductases. In addition to FADH2, oxygen and halide ions (chloride and bromide) are necessary for the halogenation reaction. The FADH2-dependent halogenases show substrate specificity and regioselectivity, and their genes have been detected in many halometabolite-producing bacteria, suggesting that this type of halogenating enzymes constitutes the major source for halometabolite formation in bacteria and possibly also in other organisms.
The excitation function and momentum distribution of η′ mesons have been measured in photon induced reactions on 12C in the energy range of 1250–2600 MeV. The experiment was performed with tagged ...photon beams from the ELSA electron accelerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the η′-nucleus potential. Within the model, the comparison indicates an attractive potential of −(37±10(stat)±10(syst)) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the η′-nucleus potential of −(10±2.5) MeV, determined by transparency ratio measurements, a search for resolved η′-bound states appears promising.
The photoproduction of η′-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500–2200 MeV. The transparency ratio has been ...deduced and compared to theoretical calculations describing the propagation of η′-mesons in nuclei. The comparison indicates a width of the η′-meson of the order of Γ=15–25 MeV at ρ=ρ0 for an average momentum pη′=1050 MeV/c, at which the η′-meson is produced in the nuclear rest frame. The inelastic η′N cross section is estimated to be 3–10 mb. Parameterizing the photoproduction cross section of η′-mesons by σ(A)=σ0Aα, a value of α=0.84±0.03 has been deduced.
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