Enzymatic Ring Opening of an Iron Corrole by Plant-Type Heme Oxygenases: Unexpected Substrate and Protein Selectivities

Heme oxygenases are widely distributed enzymes involved in the oxidative cleavage of the heme macrocycle that yields the open-chain tetrapyrrole biliverdin IX, CO, and iron. For the first time, two regioisomeric iron corroles [alpha-CH- and gamma-CH-Fe(cor)] have been utilized as artificial substrate and cofactor analogues to mammalian, plant, cyanobacterial, and bacterial heme oxygenases. The non-natural enzymatic cleavage of gamma-CH-Fe(cor), catalyzed by plant-type heme oxygenases from Arabidopsis thaliana and Synechocystis sp., happens selectively at the unexpected bipyrrolic position and yields a biomimetic biliverdin-like product. The reaction is selective for this corrole regioisomer and for plant-type heme oxygenases and is the first report of an enzymatic corrole ring opening.