Xylene is a common aromatic hydrocarbon used in the medical industry as a solvent. This pathway describes a part of how xylene is degraded in certain bacterial species. Xylene exists in different percentages in a laboratory-grade level and is of a few common kinds: m-xylene (40–65%), p-xylene (20%), o-xylene (20%) and ethylbenzene (6-20%) and traces of toluene, trimethyl benzene, phenol, thiophene, pyridine, and hydrogen sulfide. In the bigger picture of this pathway, m-xylene, p-xylene, o-xylene as well as toluene are considered, where part of the degradation processes for each of these xylene types have been illustrated. All degradation reactions here are taking place in the cytoplasm. One part of this pathway starts with 4-methylbenzoic acid / p-methylbenzoate which is a product downstream of the p-xylene degradation and forms other intermediates: cis-1,2-dihydroxy-4-methylcyclohexa-3,5-diene-1-carboxylate, 4-methylcatechol, 3-methyl-cis,cis-muconate, 4-methylmuconolactone and 3-methylmuconolactone aided by the proteins and protein complexes: toluate-1,2-deoxygenase alpha and beta subunit, cis-1,2-dihydroxycyclohexa-3,4-diene carboxylate dehydrogenase, catechol 1,2-dioxygenase, and muconate cycloisomerase I. It must be noted that the intermediate 3-methyl-cis,cis-muconate gives rise to two products in this pathway via two different reactions using the same protein muconate cycloisomerase I. The other section of this pathway demonstrates the degradation of o-methylbenzoate and m-methylbenzoate. o-Methylbenzoae degrades down to the intermediate 1,2-dihydroxy-6-methylcyclohexa-3,5-dienecarboxylate and m-methylbenzoate degrades down to the intermediate 1,2-dihydroxy-3-methylcyclohexa-3,5-dienecarboxylate. They both then degrade to the same product/intermediate 3-methylcatechol. These reactions are both catalyzed by the proteins probable ring-hydroxylating dioxygenase subunit and cis-1,2-dihydroxycyclohexa-3,4-diene carboxylate dehydrogenase respectively.

Xylene and Toluene Degradation References