Figure 1.

(a) NO redox species. NO exists as three different redox species: the NO radical (NO^•); the nitrosonium cation (NO⁺); and the NO anion (NO⁻), which reversibly transitions between species via the addition or loss of an electron. (b) NO production via l-arginine. NO production occurs endogenously by the conversion of l-arginine to l-citrulline via the intermediate N^ω-hydroxy-l-arginine. NADPH serves as an electron donor for both reactions.