Figure 1.

Interference of Semiquinone in the redox cycle. NADPH oxidase is involved in the generation of the Semiquinone form of Doxo. The Quinone form is regenerated by the presence of oxygen, forming superoxide, a highly reactive species. Indeed, superoxide interacts with nitric oxide to form the peroxynitrite anion, a potent free radical; in addition, superoxide is converted into peroxide by SOD. Hydrogen peroxide is responsible for the formation of hydroxyl radicals, leading to DNA, protein, and lipid damage. Abbreviations: SOD, Superoxide dismutase; NOs, nitric oxide synthetase.