title: Evidence from mechanistic probes for distinct hydroperoxide rearrangement mechanisms in the intradiol and extradiol catechol dioxygenases.
abstract: Three mechanistic probes were used to investigate whether the Criegee rearrangement step of catechol 1,2-dioxygenase (CatA) from Acinetobacter sp. proceeds via a direct 1,2-acyl migration, via homolytic O-O cleavage, or via a benzene oxide-oxepin rearrangement. Incubation of CatA with 3-chloroperoxybenzoic acid led to the formation of a 9:1 mixture of 2-chlorophenol and 3-chlorophenol, via a mechanism involving O-O homolytic cleavage. Incubation of CatA with 2-hydroperoxy-2-methylcyclohexanone led to formation of 5,6-diketoheptan-1-ol, also consistent with an O-O homolytic cleavage mechanism, and not consistent with a direct 1,2-acyl migration. No reaction product was isolated from incubation of CatA with 6-hydroxymethyl-6-methylcyclohexa-2,4-dienone, an analogue that is able to undergo the benzene oxide-oxepin rearrangement, but not able to undergo O-O homolytic cleavage. In contrast, incubation of extradiol dioxygenase MhpB from Escherichia coli with 6-hydroxymethyl-6-methylcyclohexa-2,4-dienone led to the formation of a 2-tropolone ring expansion product, consistent with a direct 1,2-alkenyl migration for extradiol cleavage. Taken together, the results imply different mechanisms for the Criegee rearrangement steps of intradiol and extradiol catechol dioxygenases: a direct 1,2-alkenyl migration for extradiol cleavage and an O-O homolytic cleavage mechanism for intradiol cleavage.
authors.affiliation: Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Meite
authors.initials: M
authors.lastname: Xin
authors.forename: Timothy D H
authors.initials: TD
authors.lastname: Bugg
mesh_terms: D000150:Acinetobacter / Q000201:enzymology; D002384:Catalysis; D050548:Catechol 1,2-Dioxygenase / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism*; D010545:Peroxides / Q000378:metabolism
chemical_list: D010545:Peroxides; D006861:Hydrogen Peroxide; D010105:Oxygenases; D050548:Catechol 1,2-Dioxygenase; C439587:extradiol dioxygenase