TOL PLASMID-SPECIFIED XYLENE OXYGENASE IS A WIDE SUBSTRATE RANGE MONOOXYGENASE CAPABLE OF OLEFIN EPOXIDATION

Xylene oxygenase, which is encoded on the TOL plasmid pWWO of Pseudomo nas putida mt-2, is a key enzyme system in the degradation of toluene and xylenes by this organism. It was expressed in an Escherichia coli recombinant strain carrying the xy1MA structural genes. This recombina nt, which expressed xylene oxygenase from the heat-shock induced lambd a P-L promoter, was analyzed for its potential as a biocatalytic tool so as to effect the oxidation of side chains of aromatic hydrocarbons to the corresponding alcohols. Compounds that were tested as potential substrates carried different substituents on the aromatic ring at ort ho, meta, and para positions, relative to the methyl moiety. Products that accumulated after administration of the aromatic hydrocarbons to concentrated suspensions of the recombinant were identified by gas cho matography and mass spectrometry. Toluene derivatives with ortho subst ituents could not serve as substrates for the biocatalyst, whereas a n umber of meta- or parasubstituted analogs were efficiently oxidized to the corresponding benzylalcohols. Bioconversion of the substrates by resting cells varied from 3 mu mol min(-1) g(-1) cell dry weight for 1 ,3,5-trimethylbenzene to 18 mu mol min(-1) g(-1) cell dry weight for m eta-xylene. Whole cells that expressed xylene oxygenase did catalyze t he oxidation of the methyl substituent attached to a benzene ring, but no conversion of n-alkylbenzene derivatives with longer side chains w as observed. Although the ethyl group of ethylbenzene could not be con verted by the biocatalyst, cells containing xylene oxygenase were capa ble of oxidizing the ethylene side group of styrene to produce styrene epoxide.