EPR Characterization of the Heme Oxygenase Reaction Intermediates and Its Implication for the Catalytic Mechanism

摘要

Heme oxygenase (HO) catalyzes the regiospecific degradation of heme to biliverdin by using three O_2 molecules and seven electrons. The enzyme binds one equivalent of heme to form the heme complex, and electron donation initiates the three stepwise oxygenase reactions through the two novel heme derivatives, α-hydroxyheme and verdoheme, during which CO and free Fe are also produced. EPR has been used to study electronic and coordination structures of the HO catalytic intermediates, including the ferric hydroperoxo active species generated by one-electron reduction of the ferrous oxy form. A combination of the novel characteristics of the reaction intermediates and the protein environment are responsible for the unique HO enzyme catalytic mechanism.