The N₂O₃-forming reaction of nitrite and hemoglobin may regulate export of NO from the erythrocyte. Hemoglobin deoxygenation (purple) occurs preferentially at the submembrane of the red blood cell as it traverses the arteriole. Nitrite reacts with deoxygenated hemoglobin to make methemoglobin and NO. Methemoglobin binds nitrite to form an adduct with some Fe⁺²-NO₂ character (Hb-NO₂^•). This species reacts quickly with NO, forming N₂O₃, which can diffuse out of the red cell, later forming NO and effecting vasodilation and/or forming nitrosothiols (SNO). Low-molecular-weight nitrosothiols may contribute to exportable vasodilatory activity. The Hb abbreviation indicates ferrous deoxyhemoglobin (Fe⁺²). Figure is reproduced from Basu et al⁴⁶  with permission.