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Journal of Bacteriology, July 2001, p. 4288-4295, Vol. 183, No. 14
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.14.4288-4295.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Succinyl-CoA:(R)-Benzylsuccinate CoA-Transferase: an Enzyme of the Anaerobic Toluene Catabolic Pathway in Denitrifying Bacteria†

Christina Leutwein and Johann Heider*

Mikrobiologie, Institut für Biologie II, Universität Freiburg, 79104 Freiburg, Germany

Received 18 September 2000/Accepted 30 April 2001

Anaerobic microbial toluene catabolism is initiated by addition of fumarate to the methyl group of toluene, yielding (R)-benzylsuccinate as first intermediate, which is further metabolized via beta -oxidation to benzoyl-coenzyme A (CoA) and succinyl-CoA. A specific succinyl-CoA:(R)-benzylsuccinate CoA-transferase activating (R)-benzylsuccinate to the CoA-thioester was purified and characterized from Thauera aromatica. The enzyme is fully reversible and forms exclusively the 2-(R)-benzylsuccinyl-CoA isomer. Only some close chemical analogs of the substrates are accepted by the enzyme: succinate was partially replaced by maleate or methylsuccinate, and (R)-benzylsuccinate was replaced by methylsuccinate, benzylmalonate, or phenylsuccinate. In contrast to all other known CoA-transferases, the enzyme consists of two subunits of similar amino acid sequences and similar sizes (44 and 45 kDa) in an alpha 2beta 2 conformation. Identity of the subunits with the products of the previously identified toluene-induced bbsEF genes was confirmed by determination of the exact masses via electrospray-mass spectrometry. The deduced amino acid sequences resemble those of only two other characterized CoA-transferases, oxalyl-CoA:formate CoA-transferase and (E)-cinnamoyl-CoA:(R)-phenyllactate CoA-transferase, which represent a new family of CoA-transferases. As suggested by kinetic analysis, the reaction mechanism of enzymes of this family apparently involves formation of a ternary complex between the enzyme and the two substrates.

* Corresponding author. Mailing address: Mikrobiologie, Institut für Biologie II, Universität Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany. Phone: 49-761-203-2774. Fax: 49-761-203-2626. E-mail: heiderj{at}uni-freiburg.de.

dagger Dedicated to W. Buckel on the occasion of his 60th birthday.

Journal of Bacteriology, July 2001, p. 4288-4295, Vol. 183, No. 14
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.14.4288-4295.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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