Extradiol

Nitrotoluene is degraded by a strain of Mycobacterium sp. via the corresponding 4-amino-3-hydroxytoluene (Spiess et al. 1998) this is dimerized abiotically to form a dihydrophenox-azinone, and after extradiol cleavage to 5-methylpyridine -2-carboxylate (Figure 2.2d). 

Extradiol (or meta) fission by catechol 2,3-dioxygenase breaks the bond between one of the hydroxyl groups and the adjacent nonhydroxylated carbon atom. Extradiol 2,3-fission enzymes have been divided into three major classes (Table 3.1) (Spence et al. 1996 Peng et al. 1998). 

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

Distal fission Although substituted catechols generally undergo extradiol fission, this may produce toxic metabolites, and can be circumvented by regioselective 1,6-dioxygenation. This is rather uncommon but it has been observed in a number of degradations ... 

There are a few extradiol-fission dioxygenases that are dependent on metals other than Fe. 

Dihydroxyphenylacetate extradiol dioxygenase from Klebsiella pneumoniae strain M5al contains magnesium and is not activated by Fe (Gibello et al. 1994). 

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 ... 

Boldt YR, Ml Sadowsky, LBM Ellis, L Que, LP Wackett (1995) A manganese-dependent dioxygenase from Arthrobacter globiformis CM-2 belongs to the major extradiol dioxygenase family. J Bacterial 177 1225-1232. 

Spence EL, M Kawamukai, J Sanvoisin, H Braven, TDH Bugg (1996) Catechol dioxygenases from Escherichi coli (MhpB) and Alcaligenes eutrophus (MPCI) sequence analysis and biochemical properties of a third family of extradiol dioxygenases. J Bacteriol 178 5249-5256. 

C subfamily of type 1 extradiol dioxygenases (Mars et al. 1999). The alternative extradiol fission of 3-chlorocatechol may take place between the 1 and 6 positions (distal fission), and this has been shown for the 2,3-dihydroxybiphenyl 1,2-dioxygenase from the naphthalene sulfonate degrading Sphingomonas sp. strain BN6 (Riegert et al. 1998). 

Riegert U, G Heiss, P Fischer, A Stolz (1998) Distal cleavage of 3-chlorocatechol by an extradiol dioxygenase to 3-chloro-2-hydroxymuconic semialdehyde. J Bacterial 180 2849-2853. 

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