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  • 1
    Electronic Resource
    Electronic Resource
    Demethylation and degradation of phenylmethylethers by the sulfide-methylating homoacetogenic bacterium strain TMBS 4 (1993)
    Springer
    Archives of microbiology 159 (1993), S. 308-315 
    Details
    ISSN: 1432-072X
    Keywords: Methyl transfer ; Demethylation ; Methoxylated aromatic compounds ; Ether cleavage ; Corrinoids ; Homoacetogenic bacteria ; Phloroglucinol pathway ; Dimethylsulfide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Biochemical studies on anaerobic phenylme-thylether cleavage by homoacetogenic bacteria have been hampered so far by the complexity of the reaction chain involving methyl transfer to acetyl-CoA synthase and subsequent methyl group carbonylation to acetyl-CoA. Strain TMBS 4 differs from other demethylating homoacetogenic bacteria in using sulfide as a methyl acceptor, thereby forming methanethiol and dimethylsulfide. Growing and resting cells of strain TMBS 4 used alternatitively CO2 as a precursor of the methyl acceptor CO for homoacetogenic acetate formation. Demethylation was inhibited by propyl iodide and reactivated by light, indicating involvement of a corrinoid-dependent methyltransferase. Strain TMBS 4 contained ca. 750 nmol g dry mass-1 of a corrinoid tentatively identified as 5-hydroxybenzimidazolyl cobamide. A photometric assay for measuring the demethylation activity in cell extracts was developed based on the formation of a yellow complex of Ti3+ with 5-hydroxyvanillate produced from syringate by demethylation. In cell extracts, the methyltransfer reaction from methoxylated aromatic compounds to sulfide or methanethiol depended on reductive activation by Ti3+. ATP and Mg2+ together greatly stimulated this reductive activation without being necessary for the demethylation reaction itself. The specific activity of the transmethylating enzyme system increased proportionally with protein concentration up to 3 mg ml-1 reaching a constant level of 20 nmol min-1 mg-1 at protein concentrations ≥ 10 mg ml-1. The specific rate of activation increased in a non-linear manner with protein concentration. Strain TMBS 4 degraded gallate, the product of sequential demethylations, to 3 acetate through the phloroglucinol pathway as found earlier with Pelobacter acidigallici.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290912
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  • 2
    Electronic Resource
    Electronic Resource
    Specificity of O-demethylation in extracts of the homoacetogenic Holophaga foetida and demethylation kinetics measured by a coupled photometric assay (1997)
    Springer
    Archives of microbiology 167 (1997), S. 363-368 
    Details
    ISSN: 1432-072X
    Keywords: Key words Anaerobic degradation ; Methoxylated ; aromatic compounds ; Dimethylsulfide ; Methyl ; transfer ; Ether cleavage ; Phloroglucinol reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetics and specificity of O-demethylation were studied in cell-free extracts of the strictly anaerobic, methanethiol- and dimethylsulfide-producing homoacetogen Holophaga foetida strain TMBS4 with methanethiol and tetrahydrofolate (H4folate) as methyl acceptors. Extracts of cells grown with 3,4,5-trimethoxybenzoate contained an enzyme system that demethylated various phenyl methyl ethers with at least one ortho-positioned hydroxyl or methoxyl group (the ortho system) and also contained a decarboxylase. Extracts of cells grown with 3,5-dihydroxyanisole contained an enzyme system with a novel specificity that demethylated only the meta-hydroxylated compounds 3,5-dihydroxyanisole and 3-hydroxyanisole (the meta system) and lacked a decarboxylase. H4folate-dependent demethylation produced CH3-H4folate. For a photometric in vitro assay of the meta system, the NADPH-consuming phloroglucinol reductase (PR) reaction was coupled to the phloroglucinol-yielding demethylation of 3,5-dihydroxyanisole. The kinetics of the indicator enzyme PR were studied. The cell extract had a high and stable specific PR activity. PR was inhibited by phloroglucinol (substrate inhibition) and the substrate analogue 3,5-dihydroxyanisole. Doubling the PR activity of the coupled enzyme assay by additions of a PR-enriched fraction had no effect, showing that the PR activity supplied by cell extract did not limit reaction rates. Demethylation activity of the meta system with either methyl acceptor increased with the square of the protein concentration. With H4folate, the in vivo activity could be attained. Kinetic parameters for the methyl acceptors were determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050456
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