Due to their toxicity and recalcitrance, microbial degradation of cyclic biaryl ethers has recently been an area of prolific scientific investigation, as well as intense public concern. Dibenzofuran and its chlorinated derivatives, some of the simplest representatives of this class of compounds, are industrially produced as intermediates and by-products of a multitude of different processes, only some of which include coal combustion and gasification, petroleum combustion, the manufacture of pesticides, and the bleaching of pulp at paper mills. The first transformation in dibenzofuran degradation is effected by a three-component class IIA dioxygenase system, dibenzofuran 4,4a-dioxygenase, which attacks in angular position (acting upon a pair of carbons, one of which is involved in the bridge between two rings). Electrons are transferred from NADH by one of two reductase monomers to a putidaredoxin-type [2Fe-2S] ferredoxin component, which in turn transfers the electrons to the dioxin dioxygenase moiety (Bunz and Cook, 1993, Armengaud and Timmis, 1997).
In Sphingomonas sp. RW1 and several other organisms, multiple isofunctional enzymes have been discovered for each of the steps in the degradation of dibenzofuran. It has been postulated (Armengaud and Timmis, 1997) that this may be due to the common expression of two separate pathways for dibenzofuran and biphenyl, the latter of which is also a growth source for some dibenzofuran-degrading microorganisms.
The following is a text-format dibenzofuran pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in Graphic (8k) format.
Dibenzofuran Sphingomonas sp. RW1, HH19k Brevibacterium sp. DPO 1361 Terrabacter sp. DPO360 Staphylococcus auricularis DBF63 | | | | dibenzofuran 4,4a-dioxygenase | | v 2,2',3-Trihydroxybiphenyl | | | | 2,2',3-trihydroxybiphenyl dioxygenase | | v 2-Hydroxy-6-oxo-6-(2-hydroxyphenyl)- hexa-2,4-dienoate (HOHPDA) | | | | 2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid hydrolase | | v Salicylate + 2-Oxopent-4-enoate | | | | | | | | | | V v to the Intermediary Napthalene Metabolism pathway (KEGG)
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