Extradiol ring fission

The degradation of xanthone by Arthrobacter sp. strain GFBIOO closely resembled the pathways used for carbocyclic compounds. In a yeast-supplemented medium, initial dioxygenation to the 3,4-dihydrodiol was followed by dehydrogenation to 3,4-dihydroxyxanthone and extradiol ring fission to a coumarin and subsequent production of 2,5-dihydroxybenzoate (Figure 10.38) (Chen and Tomasek 1991 Tomasek and Crawford 1986). 

The second large group of ring-fission dioxygenases are used for the degradation of ortho-dihy-droxybenzoates including, 2,3-, 3,4-, and 4,5-dihydroxybenzoate. As for simple catechols, hssion may be either intradiol or extradiol, and the choice between them depends on the organism ... 

After formation of the 1,2-dihydroxy compounds, ring fission is mediated by 1 2 (intradiol fission) or 2 3 (extradiol and distal fission) dioxygenases. There are, however, important variations in the pathways used by various groups of microorganisms ... 

Ring fission. Ring fission of substituted catechols may take place by three pathways intradiol (ortho), extradiol (meta), or distal (1 6) fission. Although extradiol fission is generally preferred for substituted catechols, the product from extradiol fission of... 

Attention has been drawn in Section 4.4.2 to the ability of naphthalene dioxygenase from Pseudomonas sp. strain 9816-4 to produce dibenzothiophene a s-l,2-dihydrodiol (Resnick and Gibson 1996). The transformation of naphtho[2,l-fr]thiophene and naphtho[2,3-fr]thiophene by Pseudomonas sp. strains grown with 1-methylnaphthalene has been examined (Knopp et al. 1997) as for the corresponding PAHs, the angular substrate (naphtho[2,l-b]thiophene) was more readily tranformed with the formation of hydroxybenzothiophene carboxylates by dioxygenation of the outer benzene ring followed by extradiol fission. 

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