Ferredoxin-Mediated Reactivation of Catechol Dioxygenase Improves Aromatic Ring Cleavage in Pseudomonads
Cleavage of the aromatic ring is a critical step in the biodegradation of aromatic hydrocarbons and is generally catalyzed by dioxygenases. These enzymes incorporate each atom of molecular oxygen in diol substrates carrying two hydroxyl groups on two adjacent carbons of the aromatic ring, and eventually cause the opening of the ring. They are classified in two families depending on the mode of scission of the aromatic substrates. Intradiol dioxygenases cleave the aromatic ring between the two hydroxyls groups, whereas extradiol enzymes cleave the ring in a position adjacent to the diol. The two groups of enzyrnes share no amino acid sequence similarities, and are also structurally distinct in that the former contain a non-heme ferric ion at the catalytic site, and the latter contain a ferrous ion (Harayama and Rekik, 1989). The catechol 2,3-dioxygenase (XylE) of the TOL pathway in Pseudomonas putida mt2 is a typical extradiol dioxygenase which utilizes catechol and methyl-substituted catechols as substrates. Like many extradiol dioxygenases, it is a rather labile enzyme which tends to inactivate during catalytic turnover, or upon exposure to air oxygen. Inactivation is caused by oxidation of the ferrous iron atom at the enzyme active site. In the presence of certain substrates such as 4-methylcatechol and chlorocatechols, the enzyme rapidly loses activity (Bartels et al., 1984; Cerdan et al., 1995).
KeywordsPhenol Cysteine Lysine Arginine Biodegradation
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