S-nitrosylated hemoglobin (SNO-Hb)

S-nitrosylated hemoglobin (SNO-Hb) is a post-translationally modified form of hemoglobin that functions as a critical regulator of the "three-gas respiratory cycle," which involves the transport of oxygen, carbon dioxide, and nitric oxide (NO) (Stamler et al., 1997; McMahon et al., 2005). It is formed by the covalent attachment of an NO group to the conserved cysteine 93 residue of the beta-globin chain (βCys93) (RCSB PDB). This process is allosterically regulated: in the lungs, high oxygen tension promotes the formation of SNO-Hb, while in hypoxic peripheral tissues, the transition of hemoglobin to its deoxygenated state triggers the release of NO bioactivity (Zhang et al., 2016; Piantadosi, 2016). The released NO induces vasodilation in the microvasculature, effectively coupling local blood flow to metabolic demand and ensuring adequate tissue oxygenation (Reynolds et al., 2013). Deficiencies in SNO-Hb levels or impaired release mechanisms are linked to the pathophysiology of several diseases, including sickle cell disease, heart failure, and pulmonary arterial hypertension (Zhang et al., 2016; NIH, 2023). Therapeutic strategies, such as the use of NO donors or S-nitrosylating agents, are being explored to restore this vital vasodilatory mechanism and protect against ischemic injury (ClinicalTrials.gov, 2023).

Other names

S-nitrosohemoglobinSNOHbNitrosylated hemoglobinS-nitroso-hemoglobin

Allosteric release of nitric oxide bioactivity during the transition of hemoglobin from the oxygenated (R) to deoxygenated (T) state, which induces microvascular vasodilation and improves tissue oxygenation (Stamler et al., 1997; Zhang et al., 2016).