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Archives of Microbiology

, Volume 167, Issue 6, pp 363–368 | Cite as

Specificity of O-demethylation in extracts of the homoacetogenic Holophaga foetida and demethylation kinetics measured by a coupled photometric assay

  • Jan-Ulrich Kreft
  • B. Schink
Original paper

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.

Key words Anaerobic degradation Methoxylated aromatic compounds Dimethylsulfide Methyl transfer Ether cleavage Phloroglucinol reductase 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • Jan-Ulrich Kreft
    • 1
  • B. Schink
    • 1
  1. 1.Fakultät für Biologie, Universität Konstanz, D-78434 Konstanz, Germany Tel. +49-7531-88-2140; Fax +49-7531-88-2966 e-mail: bernhard.schink@uni-konstanz.deDE

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