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The left pathway presented below is unique in that the initial step does not involve an oxygenation of the sulfonated carbon, but monooxygenation of the methyl group. However, the final, desulfonating step is a dioxygenation catalyzed by Fe2+-activated 4-sulfobenzoate 3,4-dioxygenase.
Alicaligenes sp. strain O-1 (Junker et al. (1994), is thought to contain two independent operons encoding desulfonative pathways, with the enzymes encoded displaying low substrate specificity. The middle pathway below reproduces the initial desulfonation reaction of TS, which can be catalyzed by 2-aminobenzenesulfonate dioxygenase system (2ASDOS) or benzenesulfonate dioxygenase system (BSDOS). There is a EAWAG-BBD reaction page for each enzyme.
Little is known about the details of the transformation of TS into 4-hydroxytoluene, although further investigation is currently underway. 'Toluene-4-sulfonate monooxygenase' is a proposed name, and 1.14.13.- a proposed E.C. code, for the reaction enzyme. Pseudomonas putida strain S-313 catalyzes only desulfonation of TS, which can serve as its sole source of sulfur. Strain S-313 leaves 4-hydroxytoluene unmetabolized, although 4-hydroxytoluene is a metabolite which is readily catabolized by other bacteria, as indicated in the EAWAG-BBD toluene pathway.
The following is a text-format toluene-4-sulfonate pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (15k) format.
Toluene-4-sulfonate Toluene-4-sulfonate Toluene-4-sulfonate Pseudomonas putida S-313 | | | | | | toluene- | toluene-4-sulfonate | 2ASDOS or | 4-sulfonate | methyl-monooxygenase | BSDOS | monooxygenase | | | v v v 4-Sulfobenzyl alcohol 4-Methylcatechol 4-Hydroxytoluene | | | | | | | 4-sulfobenzyl alcohol | | | dehydrogenase | | | | | v v v 4-Sulfobenzaldehyde to the to the | p-Xylene Pathway Toluene Pathway | | 4-sulfobenzaldehyde | dehydrogenase | v 4-Sulfobenzoate | | | 4-sulfobenzoate | 3,4 dioxygenase | v Protocatechuate | | | | | v to the 2,4-Dichlorobenzoate Pathway
Page Author(s): Kathryn Eisenmann and Ryan McLeish
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