Toluene monooxygenation

Toluene/o-xylene monooxygenase in P. stutzeri strain 0X1 carried ont snccessive monooxygenation of o-xylene (Bertoni et al. 1998), and the tolnene-4-monooxygenase of Pseudomonas mendocina KRl and tolnene-3-monooxygenase of Ralstonia pickettii PKOl can hydroxylate benzene, tolnene, and o-xylene (Tao et al. 2004 Vardar and Wood 2004). 

Lehning A, U Fgock, R-M Wittich, KN Trmmis, DH Pieper (1997) Metabolism of chlorotoluenes by Burk-holderia sp. strain PS12 and toluene dioxygenase of Pseudomonas putida FI evidence for monooxygenation by toluene and chlorobenzene dioxygenases. Appl Environ Microbiol 63 1974-1979. 

Wackett LP, LD Kwart and DT Gibson (1988) Benzylic monooxygenation catalyzed by toluene dioxygenase from Pseudomonas putida. Biochemistry 27 1360-1367. 

Zhou N-Y, A Jenkins, CKN Chan, KW Chion, DJ Leak (1999) The alkene monooxygenase from Xanthobacter strain Py2 is closely related to aromatic monooxygenases and catalyzes aromatic monooxygenation of benzene, toluene, and phenol. Appl Environ Microbiol 65 1589-1595. 

Xanthobacter sp. strain Py2 may be grown with propene or propene oxide. On the basis of amino acid sequences, the monooxygenase that produces the epoxide was related to those that catalyzes the monooxygenation of benzene and toluene (Zhou et al. 1999). The metabolism of the epoxide is initiated by nucleophilic reaction with coenzyme M followed by dehydrogenation (Eigure 7.13a). There are alternative reactions, both of which are dependent on a pyridine nucleotide-disulfide oxidoreductase (Swaving et al. 1996 Nocek et al. 2002) ... 

As an alternative, successive monooxygenation of benzene to phenol, catechol, and 1,2,3-trihydroxybenzene may be accomplished by the toluene 4-monooxygenase of Pseudomonas mendocina strain JKRl and the 3-monooxygenase of Ralstonia Pseudomonas) pickettii strain PKOl (Taoetal. 2004). 

Degradation of toluene may also take place in different species of Pseudomonas by initial monooxygenation at the 2-, 3-, or 4-positions. The situation for toluene monooxygenases has been confusing. However, it is now recognized that only the following two initial reactions take place ... 

FIGURE 8.3 Aerobic degradation of toluene by (a) side-chain oxidation, (b) dioxygenation of the ring, and (c) monooxygenation. (From Neilson, A.H. and Allard, A.-S. The Handbook of Environmental Chemistry, Springer, 1998. With permission.)... 

Toluene is oxidized by purified naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4 to benzyl alcohol and ben-zaldehyde, and ethylbenzene to (S)-l-phenylethanol and acetophenone. Whereas the initial reactions involve monooxygenation, oxidation to the aldehyde and ketone are dioxygen-dependent (Lee and Gibson 1996). 

Ring monooxygenation of toluene has been found in various taxa. 

Mimoun and Roch used hydrazobenzene (PhNHNHPh) for oxygenation of cyclohexane, cyclohexene, and toluene." The most active complex was formed from FCCI2 and carboxylic acid in the presence of hydrazobenzene. Davis et al. used Fepy4Cl2 and PbC02H for the same reaction and proposed the hydroperoxide complex [Fe "(OOH) PhNNHPh)] as an active species."" Sheu et al. used Fe" complexes (Fe(PA) or Fc(DPAH)2) (PA picolinato) for the monooxygenation of saturated hydrocarbons, especially ketonization of methylenic carbons. "" This system was applied to the hydroxylation of aromatic hydrocarbons as reaction mimic for tyrosine hydroxylase."" With phenol as a reactant, the dominant product was catechol. 

Arene.. dioxygenases catalyze reactions other than dihydroxylation of aromatics. For example, toluene dioxygenase catalyzes monooxygenation of indene and indan to 1-indenol and 1-indanol, respectively [382], oxidation of polyhalogenated compounds such as trichloroethylene [eq. (24)] [363, 388-390], and stereoselective sulfoxidation of sulfides [391, 392]. 

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