Ring-Fission Dioxygenases

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 ... 

Hintner J-P, C Lechner, U Riegert, AE Kuhm, T Storm, T Reemtsma, A Stolz (2001) Direct ring fission of salicylate by a salicylate 1,2-dioxygenase activity from Pseudaminobacter salicyloxidans. J Bacterial 183 6936-6942. 

Hintner J-P, T Reemtsma, A Stolz (2004) Biochemical and molecular characterization of a ring fission dioxygenase with the ability to oxidize (substituted) salicylate(s) from Pseudaminobacter salicylatoxidans. J Biol Chem 279 37250-37260. 

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). 

An analogous pathway is used for the degradation of 5-aminosalicylate that is an intermediate in the degradation of 6-aminonaphthalene-2-sulfonate. Direct ring fission of both 5-aminosalicylate and 5-hydroxysalicylate can be accomplished by a salicylate 1,2-dioxygenase in Pseudaminobacter salicylatoxidans (Hintner et al. 2001). 

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 third alternative for ring fission of 3,4-dihydroxybenzoate is exemplified by Bacillus macerans and B. circulans that use a 2,3-dioxygenase to accomplish this (Figure 8.30b)... 

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. 

Contaminated soil has been inoculated with bacteria of established capacity for degradation of chlorobenzoates (Hickey et al. 1993). In the presence of added biphenyl, mineralization of PCBs was shown, although it was pointed out that there may exist incompatibility between the prodnction of chlorocatechols from chlorobenzoates and their inhibition of dihydroxybiphenyl-2,3-dioxygenase that catalyzes the ring fission of many PCBs. 

---