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  • 1
    ISSN: 0304-4165
    Keywords: Chitin synthetase ; Chitosome dissociation ; Digitonin
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: “Slime” variant ; Neurospora ; Chitosomes ; Chitin synthetase ; Secretory vesicles ; Invertase ; Phosphatase ; Membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cells from the “slime” variant of Neurospora crassa were broken in isotonic conditions by use of triethanolamine buffer plus EDTA. After removal of large membranous structures by low-speed centrifugation, chitosomes and secretory vesicles were separated by means of gel filtration, precipitation of membranous contaminants with Concanavalin A, and centrifugation in sucrose or glycerol gradients. Polypeptidic composition of fractions enriched in secretory vesicles or chitosomes was found to be distinct. By these criteria we concluded that chitosomes and secretory vesicles represent different populations of microvesicles. Both microvesicular populations appeared free of endoplasmic reticulum and vacuolar contaminants as demonstrated by determination of appropriate enzymatic markers.
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  • 3
    ISSN: 1432-072X
    Keywords: Chitin synthetase ; Phycomyces blakesleeanus ; Calcium-calmodulin ; Proteases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Levels of basal chitin synthetase in cell-free extracts from Phycomyces blakesleeanus were reduced by breakage of cells in the presence of EDTA or EGTA. Addition of Ca2+ to these extracts activated chitin synthetase. Maximal activation was obtained after 2 h at a Ca2+ concentration of 2–5 mM. Activation by calcium was not reduced by any protease inhibitor tested but benzamidine, whereas the weak proteolytic activity of the extracts was inhibited by antipain. Larger levels of chitin synthetase activation were obtained by the simultaneous addition of calcium and calmodulin in most, but not all extracts. This further activation by calmodulin was prevented by TFP. ATP or cAMP did not stimulate activation by calcium or calcium-calmodulin.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1615-6102
    Keywords: Vesicles ; Phycomyces ; Calcium ionophore ; Chitin synthetase ; Invertase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Hyphal elongation, chitin synthesis in vivo, and invertase secretion inPhycomyces blakesleeanus were all inhibited almost instantly by the addition of 5–10 μM calcium ionophore A 23187. Protein biosynthesis was inhibited in these conditions by 30–50%. The ionophore did not affect cell respiration for at least 40 min. Effect on chitin biosynthesis was not due to alterations of the chitin synthetase levels or its activity; nor to impairement in GlcNAc metabolism. In drug-treated cells the number of apical vesicles was severely reduced even at very short periods of incubation, and these low numbers remained constant for at least 60 min of incubation with the ionophore. We suggest that the ionophore collapses the cellular calcium gradient and/or interferes with the normal electrical transhyphal current. As a consequence, formation and migration of apical vesicles are inhibited. These results are further evidence of the role of vesicles in fungal tip growth and exhibit the fact that active chitin synthetase is short-lived in vivo demanding its continuous supply by chitosomes to the cell surface.
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  • 5
    ISSN: 1617-4623
    Keywords: Phycomyces ; Chitin synthetase ; Nikkomycin ; N-acetylglucosamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mutants resistant to nikkomycin, an inhibitor of chitin biosynthesis, were isolated after exposure of wild-type spores of the fungus Phycomyces blakesleeanus to N-methyl-N′-nitro-N-nitrosoguanidine. Genetic analysis revealed that nikkomycin resistance was due to mutations in a single gene, chsA. Mutants and wild type grew equally well in the absence of nikkomycin. In contrast to the wild type, whose spore germination and mycelial growth were inhibited by 5 μM nikkomycin, chsA mutants grew reasonably well in the presence of 50 μM nikkomycin. Chitin synthesis in vivo was much less affected by the drug in the mutants than in the wild type. Resistance was not due to impaired uptake or detoxification of the drug. Analysis of the kinetics of chitin synthesis in vitro showed that the mutants had a decreased Ka for the allosteric activator, N-acetylglucosamine, and gross alterations in nikkomycin inhibition kinetics. These results indicate that chsA is the structural gene for chitin synthetase, or at least for the polypeptide that bears the catalytic and allosteric sites.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9699
    Keywords: Chitin synthetase ; chitosomes ; Mucorales
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stability of chitin synthetase in cell-free extracts from mycelial fungi was markedly improved by the presence of sucrose in the homogenization media. Breakage of mycelium in sucrose-containing buffer yielded enzyme preparations from which chitosomal chitin synthetase could be purified by a procedure involving ammonium sulfate precipitation, gel filtration and centrifugation in sucrose density gradients. Purified chitosomes catalyzed the synthesis of chitin microfibrils in vitro upon incubation with substrate and activators. Chitosomal chitin synthetase from the filamentous form of M. rouxii was similar to the enzyme from yeast cells, except for the poorer stability and diminished sensitivity to GlcNAc activation of the former.
    Type of Medium: Electronic Resource
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