Affiliation:
1. Mikrobiologie, Institut für Biologie II, Universität Freiburg, 79104 Freiburg, Germany
Abstract
ABSTRACT
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 β-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 α
2
β
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
75 articles.
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