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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
3
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pubmed:dateCreated |
1995-2-7
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pubmed:abstractText |
The previously studied complete methyl transfer sequence of tetrahydrofolate-dependent O-demethylation catalyzed by Holophaga foetida strain TMBS4 extracts was separated into two steps using cobalamins as non-physiological substrates: electrochemically produced cob(I) alamin served as methyl acceptor for phenyl methyl ether demethylation, yielding methylcob(III)alamin (reaction I), and methylcob(III)alamin served as donor for tetrahydrofolate methylation, yielding 5-methyl tetrahydrofolate (reaction II). Both reactions were measured with a new and direct photometric assay of cob(I)alamin methylation (or the reverse reaction) at 540 nm, the isobestic wavelength of the cob(II)alamin/cob(I)alamin redox couple (delta epsilon 540 = 4.40 nM-1.cm-1. The rates of reactions I and II were proportional to protein concentration, unlike the complete reaction sequence. Small components of cell extract did not affect activity of reactions I and II. Isovanillate demethylation by extracts of synringate-grown cells (reaction I) required reductive activation by cob(I)alamin and was inhibited and inactivated by cob(II)alamin, indicating that the reaction mechanism was a nucleophilic attack of an enzyme-bound corrinoid in the reduced Co(I) state on the methyl carbon of the ether, rather than a radical attack. Only phenyl methyl ethers were demethylated; demethylation rates were enhanced by ortho-hydroxyl or para-carboxyl groups, but reduced by additional meta substituents. The rate of isovanillate demethylation was 81 nmol.min-1.(mg protein)-1 [0.76 mM cob(I)alamin] and apparent kinetic constants for cob(I)alamin were: Km = 1.2 mM, Vmax = 220 nmol min-1.(mg protein)-1, and Vmax/Km = 180 nmol.min-1.(mg protein) 1.mM-1 3,5-Dihydroxyanisole demethylation by extracts of 3,5-dihydroxyanisole-grown cells (also reaction I) was much slower. Reaction II did not require activation; specific activity and the specificity constant for methylcob(III)alamin were much lower.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/5,6,7,8-tetrahydrofolic acid,
http://linkedlifedata.com/resource/pubmed/chemical/Anisoles,
http://linkedlifedata.com/resource/pubmed/chemical/Tetrahydrofolates,
http://linkedlifedata.com/resource/pubmed/chemical/Vanillic Acid,
http://linkedlifedata.com/resource/pubmed/chemical/Vitamin B 12,
http://linkedlifedata.com/resource/pubmed/chemical/isovanillic acid,
http://linkedlifedata.com/resource/pubmed/chemical/mecobalamin
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pubmed:status |
MEDLINE
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pubmed:month |
Dec
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pubmed:issn |
0014-2956
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
15
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pubmed:volume |
226
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
945-51
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pubmed:dateRevised |
2007-7-23
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pubmed:meshHeading |
pubmed-meshheading:7813485-Anisoles,
pubmed-meshheading:7813485-Electrochemistry,
pubmed-meshheading:7813485-Gram-Negative Anaerobic Bacteria,
pubmed-meshheading:7813485-Kinetics,
pubmed-meshheading:7813485-Methylation,
pubmed-meshheading:7813485-Oxidation-Reduction,
pubmed-meshheading:7813485-Photometry,
pubmed-meshheading:7813485-Tetrahydrofolates,
pubmed-meshheading:7813485-Vanillic Acid,
pubmed-meshheading:7813485-Vitamin B 12
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pubmed:year |
1994
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pubmed:articleTitle |
O-demethylation by the homoacetogenic anaerobe Holophaga foetida studied by a new photometric methylation assay using electrochemically produced cob(I)alamin.
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pubmed:affiliation |
Fakultät für Biologie, Universität Konstanz, Germany.
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pubmed:publicationType |
Journal Article,
Research Support, Non-U.S. Gov't
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