Fig. 4.

Reaction mechanism for the oxidative aromatic ring-cleavage of HG by HGDO based on the five active site structures found in this study. (I) Fe²⁺ site before substrate binding. Water molecules occupy two coordination sites completing the octahedral arrangement of the iron ligands. (II) HG acts as a monodentate ligand. Bound HG is further stabilized by hydrogen bonds to H288 and Y346. (III) Oxidized HG (semiquinone state) is formed by reduction of dioxygen to the superoxo state. (IV) Alkylperoxo intermediate. (V) Ring-fission product. States IV and V are possibly connected by formation of gem-diol and lactone intermediates.