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  • 1
    Publication Date: 2020-09-01
    Print ISSN: 0021-9517
    Electronic ISSN: 1090-2694
    Topics: Chemistry and Pharmacology
    Published by Elsevier
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  • 2
    Publication Date: 2021-07-08
    Description: The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar’s rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10−4 to 1.1 peta–electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta–electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron’s size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta–electron volt electrons, 2.5 × 1036 ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta–electron volt protons to the production of the highest-energy gamma rays.
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A Mendelian mutant r-1 in chlamydomonas reinhardtii has been shown to make the synthesis of δ-aminolevulinic acid (ALA) insensitive to inhibition by protoporphyrin. We have now combined the r-1 mutant with the protochlorophyllideaccumulating mutant y-1. From the phenotype of the double mutant y-1 r-1 and the phenocopy produced by feeding ALA to y-1, we conclude that r-1 also makes the synthesis of ALA insensitive to the inhibition by protochlorophyllide. To explain the fact that both ALA-fed y-1 and y-1 r-1 accumulate large amounts of protoporphyrin and smaller amounts of protochlorophyllide, we propose a new control feedback loop in the porphyrin biosynthetic pathway from protochlorophyllide to the step which converts protoporphyrin to magnesium protoporphyrin.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 179 (1980), S. 259-263 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three phenotypically ‘yellow’, mendelian mutants of Chlamydomonas reinhardtii have been isolated and tested for allelism with the yellow mutant v-1a 1 and with each other. The three mutants represent three new yellow loci, two of which are located on linkage group I. Like y-1a, the mutants accumulate protochlorophyllide when grown under dim light, but have a wildtype phenotype when grown in the light. We conclude that the control of light-independent protochlorophyllide reduction is more complex than has been thought previously.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have developed a procedure for the isolation of Chlamydomonas reinhardtii mutants defective in light-dependent protochlorophyllide reduction (photoconversion), a key step in the biosynthesis of chlorophyll. Mutants were isolated by mutagenizing y-1-4, a temperature-sensitive yellow mutant blocked in the alternative light-independent protochlorophyllide reduction pathway, and screening for colonies which failed to green in the light at the restrictive temperature. Seven mutants were isolated which fail to photoconvert protochlorophyllide in photoconversion tests. All seven mutants have a single mutation at the pc-1 locus responsible for the defect in photoconversion. pc-1 maps close to y-5 on nuclear linkage group I. The pc-1 mutation is not itself temperature-sensitive because it blocks photoconversion at the permissive temperature when combined with the non-conditional yellow mutations y-5 and y-7. Cells containing the pc-1 mutation alone synthesize about 52% and 36% of the wildtype chlorophyll level in the dark and light, respectively, demonstrating that the light-independent protochlorophyllide reduction pathway in C. reinhardtii operates in the light.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A group of chlorophyll deficient mutants (br s mutants) of Chlamydomonas accumulates protoporphyrin and has poorly developed chloroplast membrane systems (Wang et al. 1974). In order to determine whether a poorly developed chloroplast membrane system is the reason for, or the result of, the inability of the br s mutants to metabolize protoporphyrin to chlorophyll, a second mutation was selected which restored chlorophyll synthesis in br s mutants. One such double mutant (br s-2 g-4) was analyzed. The double mutant br s-2 g-4 has partially restored chlorophyll synthesis, but has defective photosystem II and photosystem I electron transport as well as abnormal chloroplast ultrastructure. Since these defects are not present in cells carrying only the g-4 mutation, they are presumed to be caused by the br s-2 mutation. It is concluded that a defect in chloroplast membrane development resulting from the br s-2 mutation causes an apparent defect in magnesium chelation by protoprophyrin. This is consistant with evidence that chlorophyll biosynthesis from magnesium protoporphyrin to chlorophyll takes place on the chloroplast membranes.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-4986
    Keywords: Urinary oligosaccharides ; inositol-oligosaccharides ; glycerol-oligosaccharides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ten previously unreported oligosaccharides have been purified from the urines of human subjects using a combination of gel filtration, ion exchange, and thin-layer chromatographies. Their structures were determined by direct probe mass spectrometry, methylation analysis, and proton NMR spectroscopy of the permethylated oligosaccharide alditols. On the basis of composition, the oligosaccharides could be divided into three groups. Five oligosaccharides containing glycerol were characterized as glucosylα1-1′glycerol; glucosylβ1-1′glycerol; galactosylβ1-1′glycerol; glucosyl-1-1′(fucosyl-1-2′)glycerol and/or fucosyl-1-1′(glucosyl-1-2′)glycerol; and glucosyl-1-1′(galactosyl-1-2′)glycerol or galactosyl-1-1′(glucosyl-1-2′)glycerol. Four inositol-containing oligosaccharides were characterized as galactosylβ1 (fucosylα1)inositol,N-acetylgalactosaminylα1 (fucosylα1)inositol, fucosylα1-2galactosylβ1 (N-acetylgalactosaminylα1)inositol and fucosylα1-2galactosylβ1-4-N-acetylglucosaminylα1(N-acetylgalactosaminylα1)inositol. Finally, galactosylα1-3(fucosylα1-2)galactosylβ1-6galactosylα1-4(fucosylα1-3)glucose, an oligosaccharide with glucose at its reducing end, was tentatively identified. The significance and possible origins of the carbohydrate structures are discussed.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-4986
    Keywords: poly-N-acetyllactosamine ; glycoprotein ; glycosyltransferase ; Golgi localization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have isolated a murine cDNA coding for a β1,3-N-acetylglucosaminyltransferase enzyme ( β3GnT). This enzyme is similar in sequence to Drosophila melanogaster Brainiac and to the murine and human β1,3-galactosyltransferase family of proteins. The mouse β 3GnT protein is 397 amino acids in length and contains 7 cysteine residues that are conserved in the human orthologue. β 3GnT is a type II membrane protein localized to the Golgi apparatus. Enzyme assays with recombinant mouse β 3GnT reveal that it has a preference for acceptors with Gal(β1-4)Glc(NAc) at the non-reducing termini. Proton NMR analysis of product showed incorporation of GlcNAc in β1,3 linkage to the terminal Gal of Gal(β1-4)Glc(β1-O-benzyl). Northern blot analysis revealed the presence of a single 3.0[emsp4 ]kb transcript in all adult mouse and human organs tested, with highest levels in the kidney, liver, heart and placenta. The β 3GnT gene is also expressed in a number of tumor cell lines. The human orthologue of β 3GnT is located on chromosome 2pl5.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dense films of poly[(4-ethylphenoxy)(phenoxy)phosphazene] (PEPP), a potentially attractive ion-exchange membrane material, were crosslinked to varying degrees using UV light and a photoinitiator. This polymer contained two kinds of substituents: phenoxy groups to be used for possible functionalization (e.g., sulfonation) and ethylphenoxy side-chains for photocrosslinking, where hydrogens at the benzylic carbons could be abstracted by a photoinitiator-leaving macroradicals that after recombination formed covalent bonds. The polyphosphazene polymer was synthesized, mixed with a photoinitiator, shaped into a thin film by solvent casting, and irradiated with UV light for a specified period of time. Benzophenone (BP), was selected as the photoinitiator because it was miscible with poly-phosphazene, had the highest rate of hydrogen abstraction, and absorbed UV light of 365 nm wavelength. The half-life of benzophenone in 50 μm-thick irradiated films was determined to be 20 min. When the BP-PEPP molar ratio was increased from 0 to 0.5, the glass transition temperature increased after irradiation from -8.8 to 53.5°C. At the same time, the equilibrium swelling in dimethylacetamide, at 25°C, decreased from infinity to 0.31. Tensile strength tests of the crosslinked films revealed a nonlinear dependence on BP-PEPP molar ratio. © 1996 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0269-3879
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The catalytic effect of bases (imidazole, pyridine, Tris and triethylamine) on the peroxyoxalate chemiluminescence (PO-CL) reaction for high performance liquid chromatography (HPLC) was investigated. Imidazole increased PO-CL intensity extraordinarily, whereas the other bases (pyridine, Tris and triethylamine) did not. The peak heights of dipyridamole (coronary vasodilator) obtained using the eluents containing buffers were largest at pH 7.0, a few times less at pH 6.0 and pH 5.0, 100 times less at pH 4.0 and a few hundred times less at pH 3.0. The eluents containing buffers at pH 3, 4, 5, 6 or 7 each with imidazole increased the peak heights by a few to ten times as compared with those without imidazole, and those peak heights were within one order of magnitude. On the other hand, the eluent containing buffer at pH 2 did not affect the peak heights with or without imidazole. Bis(4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl) oxalate (TDPO) alone and bis(2,4-dinitrophenyl)oxalate (DNPO) plus TDPO were recommended to be used against eluents containing buffers of pH 5 - 7 and pH 3 - 4, respectively. Dipyridamole and benzydamine hydrochloride (anti-inflamatory drug) were separated on the ODS column and detected by the present system. The detection limits of dipyridamole and benzydamine hydrochloride were 40 amol and 270 fmol, respectively.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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