Phenol monooxygenases

Incomplete aerobic transformations may involve cometabolic transformations and reactions resulting in recalcitrant dead-end metabolites. Cometabolic o-hydroxylation of MCPs and DCPs by a phenol monooxygenase has been shown, for example, in a Pseudomonas sp. (Knackmuss Hellwig, 1978) and by the toluene dioxygenase reaction in Pseudomonas putida (Spain Gibson, 1988 Spain et al., 1989)- Cometabolic transformation of CPs is also possible in aerobic mixed culture systems. Phenol- and toluene-enriched cultures completely removed 2,4-DCP, and the toluene enrichment also removed 2,4,6-TCP and PCP (Ryding et al., 1994). This PCP attack by the toluene enrichment involved an o-hydroxylation. 

Nurk, A., L. Kasak, and M. Kivisaar. 1991. Sequence of the gene (pheA) encoding phenol monooxygenase from Paseudomonas sp. EST1001 expression in Escherichi coli and Pseudomonas putida. Gene 102 13-18. 

As mentioned above, even though tyrosinase and CO have similar active sites, CO lacks o-phenol monooxygenase activity. This could be explained by the differences of the vacant space of the substrate-binding pocket and the flexibility of the active site (24). In CO, the Phe261 side chain is located just above the Cua site, and it could inhibit substrate binding. Also, in CO, His 109 has the unusual covalent bond with Cys92 (Fig. 12), generating the inflexibility of His 109 and catalytic specifleity (24). 

Aromatic carbon-hydrogen bond Phenols Synthesis of phenols Monooxygenase, dioxygenase, peroxidase... 

Wieser M, B Wagner, J Eberspacher, F Lingens (1997) Puriflcation and characterization of 2,4,6-trichloro-phenol-4-monooxygenase, a dehalogenating enzyme imm Azotobacter sp. strain GPL J Bacterial 179 202-208. 

Xanthobacter sp. strain Py2 was isolated by enrichment on propene that is metabolized by initial metabolism to the epoxide. The monooxygenase that is closely related to aromatic monooxygenases is able to hydroxylate benzene to phenol before degradation, and toluene to a mixture of 2-, 3-, and 4-methylphenols that are not further metabolized (Zhou et al. 1999). 

Monooxygenases generally initiate the degradation of phenols and their ethers ... 

Kadiyala V, JC Spain (1998) A two-component monooxygenase catalyzes both the hydroxylation of -nitro-phenol and the oxidative release of nitrite from 4-nitrocatechol in Bacillus sphaericus JS905. Appl Environ Microbiol 64 2479-2484. 

Tao Y, A Fishman, WE Bentley, TK Wood (2004) Oxidation of benzene to phenol, catechol, and 1,2,3-trihydroxybenzene by toluene 4-monooxygenase of Pseudomonas mendocina KR 1 and toluene... 

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. 

The degradation of phenol is initiated by hydroxylation using a single-component NAD(P)H-depen-dent monooxygenase encoded by pheA (Nurk et al. 1991). In Bacillus thermoglucosidasius, however, the hydroxylase is a two-component system encoded by pheAl and pheA2, and hydroxylation requires supplementation by the second component with FAD(NADH) (Kirchner et al. 2003). 

Kirchner U, AH Westphal, R Muller, WJH van Berkel (2003) Phenol hydroxylase from Bacillus thermoglucosi-dasius A7, a two-component monooxygenase with a dual role for PAD. J Biol Chem 278 47545-47553. 

The C-B bond in boronates is fissioned by monooxygenases in both alkyl (Latham and Walsh 1986), and in aryl boronates inclnding snbstitnted phenylboronates and naphthylboronates with prodnction of the corresponding phenols (Negrete-Raymond et al. 2003). 

In the light of possible concern over the introduction of phenol into aquifers, mutant strains of Burkholderia (Pseudomonas) cepacia strain G4 in which toluene 2-monooxygenase is constitutive have been examined in microcosm experiments. Effective removal of TCE could be demonstrated (Krumme et al. 1993 Munakata-Marr et al. 1996), although in the first experiment serious loss in the viability of the cells occurred during the 10-week incubation. This aspect therefore presents a remaining challenge. 

Because LCEC had its initial impact in neurochemical analysis, it is not, surprising that many of the early enzyme-linked electrochemical methods are of neurologically important enzymes. Many of the enzymes involved in catecholamine metabolism have been determined by electrochemical means. Phenylalanine hydroxylase activity has been determined by el trochemicaUy monitoring the conversion of tetrahydro-biopterin to dihydrobiopterin Another monooxygenase, tyrosine hydroxylase, has been determined by detecting the DOPA produced by the enzymatic reaction Formation of DOPA has also been monitored electrochemically to determine the activity of L-aromatic amino acid decarboxylase Other enzymes involved in catecholamine metabolism which have been determined electrochemically include dopamine-p-hydroxylase phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase . Electrochemical detection of DOPA has also been used to determine the activity of y-glutamyltranspeptidase The cytochrome P-450 enzyme system has been studied by observing the conversion of benzene to phenol and subsequently to hydroquinone and catechol... 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

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