Extradiol aromatic dioxygenases

Figure 18-22 Some possible intermediates in the action of extradiol (left) and intradiol (right) aromatic dioxygenases. Although the steps depict the flow of pairs of electrons during the formation and reaction of peroxide intermediates, the mechanisms probably involve free radicals whose formation is initiated by 02. The asterisks show how two atoms of labeled oxygen can be incorporated into final products.

Lipscomb, J. D. (2008). Mechanism of extradiol aromatic ring-cleaving dioxygenases. Current Opinion in Structural Biology, 18, 644-649. 

Dioxygenases that open the aromatic ring in the vicinal position to the o-diols are called extradiol dioxygenases. A mononuclear Fe(II) or Mn(II) complex forms their active site. This is, for instance, the case of 2,3-dihydroxybiphenyl-1,2-dioxygenase of Pseudomonas sp. Strain KKS102, the square pyramidal geometry of which is schematized in Figure 3.3... 

Dioxygenases which act on aromatic ortho-diphenols may either cleave the aromatic ring by an intradiol pathway or by an extradiol route, as shown in equation (77),... 

---