Figure 2 - Oxygen activation by Rieske cis-diol dioxygenases.

This type of reaction requires formation of a more reactive species than is found in the extradiol dioxygenase pathway of Figure 1. One electron from the Rieske cluster and one from the Fe(II) are used to form Fe(III)-OOH, which may then form Fe(V)=O-OH as the reactive species. The structure shown is of the hydroperoxo intermediate of Pseudomonas sp. strain NCIB 9816-4 NDO with the substrate analog indole bound nearby (PDB code 1O7N)⁵². Atom color code: gray, carbon (enzyme residues); yellow, carbon (substrate); blue, nitrogen; red, oxygen; cyan, iron.