At least four different mechanisms for degradation of sulfonated aromatic compounds have been elucidated ([http://www.ncbi.nlm.nih.gov/pubmed/7946467|Kertesz et al. (1994)]), and the classification therein is based on the time of desulfonation: prior to (two different mechanisms), simultaneous with, or after ring cleavage. Catabolism of toluene-4-sulfonate (TS or TSA), a dye precursor, may progress in accordance with two of the four mechanisms, both involving desulfonation prior to ring cleavage. 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 ([http://www.ncbi.nlm.nih.gov/pubmed/8075807|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.