Figure 1. Endogenous oxidative stress.

The adventitious transfer of electrons from redox enzymes to oxygen generates a mixture of O₂⁻ and H₂O₂. These species oxidize the solvent-exposed iron centers of mononuclear Fe²⁺ enzymes and [4Fe-4S] dehydratases, provoking iron dissociation and activity loss. The H₂O₂ also reacts with the pool of loose iron, most notably leading to DNA damage from hydroxyl-radical production.