Cytochrome P450 mechanism. 1. Substrate binds to the enzyme. 2. Adrenodoxin donates an electron, reducing the heme iron. 3. Oxygen binds to Fe2+. 4. Adrenodoxin donates a second electron. 5. The bond between the oxygen atoms is cleaved, a molecule of water is released, and an Fe4+=O intermediate is formed. 6. The Fe4+=O intermediate forms the hydroxylated product and returns the iron to the Fe3+ state, ready for another reaction cycle.