Intradiol

Intradiol (or ortho) fission by catechol 1,2-dioxygenase breaks the bond between the atoms bearing the hydroxyl groups ... 

FIGURE 3.23 Alternative dioxygenation pathways for 3-substituted catechols (a) extradiol, (b) intradiol, and (c) distal. 

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 ... 

Dioxygenase. Although it is not involved in the transformation of PAHs, it may be noted for the sake of completeness that a catechol intradiol dioxygenase is involved in the fission of 1,2,4-trihydroxybenzene that is formed from a number of aromatic substrates (Rieble et al. 1994). 

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 ... 

The enzymes of alternative pathways may be induced in a given strain by growth with different substrates for example, growth of Pseudomonas putida R1 with salicylate induces enzymes of the extradiol fission pathway, whereas growth with benzoate induces those of the intradiol pathway (Chakrabarty 1972). As a broad generalization, the extradiol fission is preferred for the degradation of more complex compounds such as toluene, naphthalene, and biphenyl (Furukawa et al. 1983). 

Although the metabolism of vanillate generally involves de-O-methylation to 3,4-dihy-droxybenzoate followed by intradiol ring hssion, in Acinetobacter Iwoffii vanillate is hydroxylated to 3-0-methyl gallate, which produces pyruvate and oxalacetate in reactions that have already been noted (Sze and Dagley 1987). 

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... 

The degradation of 3-chloro-4-methylaniline by Pseudomonas cepacia strain CMAl involved ring fission of 3-chloro-4-methylcatechol by an intradiol enzyme (Stockinger et al. 1992). 

In strain RH025, a hydrolytic mechanism brought about the loss of fluoride to produce 4-hydroxybenzoate, which was further hydroxylated to 3,4-dihydroxybenzoate before intradiol ring fission (Figure 9.33a). 

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