Theoretical Study on Compound I Formation in Monooxygenation Mechanism by Cytochrome P450

The intermediate structures appearing until compound I formation in the monooxygenation reaction cycle by cytochrome P450 were determined by using the density functional theory. Protons were attached to an O 2 molecule binding to the heme iron in a reduced oxy-ferrous state. When two protons were attached to the distal O atom, O-O bond cleavage occurred, and the compound I structure was formed. The structure had an energetic advantage compared to the situation in which one proton each was connected to the proximal and distal O atoms, and the structure would catalyze oxidation of a substrate. The calculated interaction energies between substrate and oxygen ligand of heme were 3-10 kcal/mol and suggests that an interaction between the substrate and the oxygen ligand of heme was maintained through the reaction process from the O 2 incorporation to the generation of the compound I and that it contributed the stability of the reaction system.