Evidence from Mechanistic Probes for Distinct Hydroperoxide Rearrangement Mechanisms in the Intradiol and Extradiol Catechol Dioxygenases
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  • 作者:Meite Xin ; Timothy D. H. Bugg
  • 刊名:Journal of the American Chemical Society
  • 出版年:2008
  • 出版时间:August 6, 2008
  • 年:2008
  • 卷:130
  • 期:31
  • 页码:10422-10430
  • 全文大小:252K
  • 年卷期:v.130,no.31(August 6, 2008)
  • ISSN:1520-5126
文摘
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.

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