Although much attention has been focused on very reactive, high valent iron-oxo intermediates in oxygenases such as methane monooxygenase and taurine dioxygenase, recent studies show that the dominant reactive species in many other oxygenase classes are superoxo or peroxo in nature. Examples will be drawn from aromatic substrate dioxygenases from 3 different classes. Extradiol ring cleaving dioxygenases utilize Fe(II) in the active site and appear to form an Fe(II)-superoxo reactive species by coordinating electron transfer from iron to O<sub>2</sub> with a substrate-to-iron transfer. Additionally, slowly reacting Fe(III)-superoxo or Fe(III)-hydroperoxo intermediates form in second sphere mutational variants of this enzyme. Intradiol ring cleaving dioxygenases appear to form a reactive alkylperoxo intermediate in a single O<sub>2</sub> binding step facilitated by electron exchange involving the metal d-orbitals. Rieske cis-diol forming dioxygenases utilize Fe(II) in the active site and appear to react initially with the aromatic substrate using an Fe(III)-superoxo intermediate. The resulting species is subsequently stabilized by electron transfer from a reduced Rieske cluster located in the adjacent subunit of the enzyme. The structure and reactivity of the intermediates of these enzymes have been probed using transient enzyme kinetics, spectroscopy, and X-ray crystallography. Supported by NIH GM24689.

Superoxo and peroxo intermediates in oxygenase reactions

251st National Meeting (2016)

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