Applied Microbiology and Biotechnology

, Volume 57, Issue 3, pp 263–273 | Cite as

Unusual enzymes involved in five pathways of glutamate fermentation

  • W. Buckel


Anaerobic bacteria from the orders Clostridiales and Fusobacteriales are able to ferment glutamate by at least five different pathways, most of which contain enzymes with radicals in their catalytic pathways. The first two pathways proceed to ammonia, acetate and pyruvate via the coenzyme B12-dependent glutamate mutase, which catalyses the re-arrangement of the linear carbon skeleton to that of the branched-chain amino acid (2S,3S)-3-methylaspartate. Pyruvate then disproportionates either to CO2 and butyrate or to CO2, acetate and propionate. In the third pathway, glutamate again is converted to ammonia, CO2, acetate and butyrate. The key intermediate is (R)-2-hydroxyglutaryl-CoA, which is dehydrated to glutaconyl-CoA, followed by decarboxylation to crotonyl-CoA. The unusual dehydratase, containing an iron–sulfur cluster, is activated by an ATP-dependent one-electron reduction. The remaining two pathways require more then one organism for the complete catabolism of glutamate to short chain fatty acids. Decarboxylation of glutamate leads to 4-aminobutyrate, which is fermented by a second organism via the fourth pathway to acetate and butyrate, again mediated by an unusual dehydratase which catalyses the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA. The fifth pathway is the only one without decarboxylation, since the γ-carboxylate of glutamate is reduced to the amino group of δ-aminovalerate, which then is fermented to acetate, propionate and valerate. The pathway involves the oxidative dehydration of 5-hydroxyvaleryl-CoA to 2,4-pentadienoyl-CoA followed by reduction to 3-pentenoyl-CoA and isomerisation to 2-pentenoyl-CoA.


Fermentation Glutamate Pyruvate Butyrate Clostridiales 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • W. Buckel
    • 1
  1. 1.Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, 35032 Marburg, Germany

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