Dioxygenase phenolic

Metabolic pathways containing dioxygenases in wild-type strains are usually related to detoxification processes upon conversion of aromatic xenobiotics to phenols and catechols, which are more readily excreted. Within such pathways, the intermediate chiral cis-diol is rearomatized by a dihydrodiol-dehydrogenase. While this mild route to catechols is also exploited synthetically [221], the chirality is lost. In the context of asymmetric synthesis, such further biotransformations have to be prevented, which was initially realized by using mutant strains deficient in enzymes responsible for the rearomatization. Today, several dioxygenases with complementary substrate profiles are available, as outlined in Table 9.6. Considering the delicate architecture of these enzyme complexes, recombinant whole-cell-mediated biotransformations are the only option for such conversions. E. coli is preferably used as host and fermentation protocols have been optimized [222,223]. 

The metabolism of fluorophenols by phenol hydroxylase from Trichosporium cutaneum, catechol 1,2-dioxygenase from Pseudomonas arvilla strain C-1, and by the fungus Exophilia jeanselmei has been examined, and detailed NMR data were given for the ring fission flnoromnconates (Boersma et al. 1998). 

Hydroxylation and dioxygenation are not, however, mntnally exclusive, because the toluene dioxygenase from Pseudomonasputida FI hydroxylates both phenol and 2,5-dichloro-phenol with the introduction of only one atom of oxygen (Spain et al. 1989). Snbsequent degradation by dioxygenation follows established pathways in which chloride is eliminated from muconic acids after ring fission. 

Spain JC, GJ Zylstra, CK Blake, DT Gibson (1989) Monohydroxylation of phenol and 2,5-dichlorophenol by toluene dioxygenase in Pseudomonas putida FI. Appl Environ Microbiol 55 2648-2652. 

Fluorinated Muconates Formed from Fluorophenols by Phenol Hydroxylase and Catechol 1,2-Dioxygenase from Exophilia jeanselmei Fluoromuconate Metabolite Phenolic Substrate(s)... 

Biological. Soil bacteria readily decomposed o-phenylphenol but the products were not identified. By analogy to the degradation of phenol to catechol, o-phenylphenol may be converted to 3-phenylcatechol before degrading to biphenyl. Another pathway may be oxidation by a dioxygenase producing 2-hydroxy-2, 3 -dihydroxybiphenyl (Zbozinek, 1984)... 

PHENOL HYDROXYLASE CATECHOL 1,2-DIOXYGENASE CATECHOL 2,3-DIOXYGENASE CATECHOL O-METHYLTRANSFERASE CATECHOL OXIDASE... 

When a benzene ring is cleaved by a dioxygenase reaction, hydroxylation of the benzene ring usually proceeds to form catechol or phenol derivatives. When catechol derivatives are cleaved by the action of individual dioxygenases, three modes of ring fission have been demonstrated by microbial enzymes85 ... 

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. 

Spain, J. C. Gibson, D. T. (1988). Oxidation of substituted phenols by Pseudomonasputida FI and Pseudomonas sp. strain JS6. Applied and Environmental Microbiology, 54,1399-404. Spain, J. C., Zylstra, G.J., Blake, C. K. Gibson, D. T. (1989). Monohydroxylation of phenol and 2,5-dichlorophenol by toluene dioxygenase in Pseudomonas putida PI. Applied and Environmental Microbiology, 55, 2648—52. 

Introduction of ry/XYZ and xylL was via a recombinant Tn5 xy/XYZLS. The resultant strain FR1 (Pseudomonas sp. B13 Tn5 xy/XYZLS]) remained unable to use 4-methyl phenol and continued to utilize 3-chlorobenzoate via fission of the 3-chlorocatechol oxidation product as it did before the pathway was altered. However, unlike B13, FR1 was able to grow with 4-chlorobenzoate as the sole carbon source. The newly introduced toluate dioxygenase accepted 4-chlorobenzoate as a substrate, and the carboxylate dehydrogenase re-aromatized the resulting dihydrodiol to 4-chlorocatechol. 4-Chlorocatechol proved to be an acceptable substrate for the native catechol 1,2-dioxygenase. Its immediate product, 3-chloromuconate, was completely metabolized. 

The emphasis on the study of hemoproteins and the iron-sulfur proteins often distracts attention from other iron proteins where the iron is bound directly by the protein. A number of these proteins involve dimeric iron centres in which there is a bridging oxo group. These are found in hemerythrin (Section 62.1.12.3.7), the ribonucleotide reductases, uteroferrin and purple acid phosphatase. Another feature is the existence of a number of proteins in which the iron is bound by tyrosine ligands, such as the catechol dioxygenases (Section 62.1.12.10.1), uteroferrin and purple acid phosphatase, while a tyrosine radical is involved in ribonucleotide reductase. The catecholate siderophores also involve phenolic ligands (Section 62.1.11). Other relevant examples are transferrin and ferritin (Section 62.1.11). These iron proteins also often involve carboxylate and phosphate ligands. These proteins will be discussed in this section except for those relevant to other sections, as noted above. 

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