Anaerobic toluene-catabolic pathway in denitrifying Thauera aromatica: activation and beta-oxidation of the first intermediate, (R)-(+)-benzylsuccinate

Microbiology (Reading). 1999 Nov;145 ( Pt 11):3265-3271. doi: 10.1099/00221287-145-11-3265.

Abstract

Anaerobic catabolism of toluene is initiated by addition of the methyl group of toluene to the double bond of a fumarate cosubstrate to yield the first intermediate, benzylsuccinate. This reaction is catalysed by the glycyl-radical enzyme benzylsuccinate synthase, as shown for the denitrifying bacterium Thauera aromatica. Benzylsuccinate is further oxidized to benzoyl-CoA, the central intermediate of anaerobic degradation of aromatic compounds. The authors show here by experiments with cell extracts of toluene-grown T. aromatica that the pathway of benzylsuccinate oxidation requires activation of the free acid to a CoA-thioester, catalysed by a toluene-induced, reversible succinyl-CoA-dependent CoA-transferase. The product of the CoA-transferase reaction, benzylsuccinyl-CoA, is oxidized to benzoyl-CoA and succinyl-CoA in extracts of toluene-grown cells, adding proof to the proposed anaerobic toluene-catabolic pathway. The stereochemical preferences of the enzymes catalysing formation and activation of benzylsuccinate have been analysed. Benzylsuccinate synthase was found to produce exclusively (R)-(+)-benzylsuccinate, although the proposed reaction mechanism of this enzyme proceeds via radical intermediates. In accordance, the reaction of succinyl-CoA:benzylsuccinate CoA-transferase is also specific for (R)-(+)-benzylsuccinate and does not proceed with the (S)-(-)-enantiomer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anaerobiosis
  • Benzoates / metabolism
  • Culture Media / chemistry
  • Molecular Conformation
  • Oxidation-Reduction
  • Succinates / metabolism*
  • Thauera / enzymology*
  • Thauera / growth & development
  • Toluene / metabolism*
  • Transferases / metabolism*

Substances

  • Benzoates
  • Culture Media
  • Succinates
  • benzylsuccinate
  • Toluene
  • Transferases