Endothelial nitric oxide synthase (NOS3) (eNOS)

Endothelial nitric oxide synthase (eNOS), also known as NOS3, is a critical enzyme primarily located in the vascular endothelium that regulates cardiovascular health by synthesizing nitric oxide (NO) (UniProt P29474). NO acts as a potent vasodilator and signaling molecule that maintains vascular tone, inhibits platelet aggregation, and prevents leukocyte adhesion to the vessel wall (PubMed: 25135551). The enzyme's function is highly dependent on the availability of the cofactor (6R)-tetrahydrobiopterin (BH4); a reduction in BH4 or an increase in its oxidized form, dihydrobiopterin (BH2), leads to eNOS "uncoupling." In this uncoupled state, eNOS produces superoxide radicals instead of NO, which drives oxidative stress and contributes to the pathogenesis of atherosclerosis and hypertension (PubMed: 21967192). Therapeutic interventions often target eNOS to restore NO production, either through the administration of sapropterin (synthetic BH4) or by using statins to increase eNOS expression (StatPearls: NBK537031). Research into the 6S-specific affinity of BH4 analogs highlights the stereospecific requirements of the enzyme, as the natural 6R-isomer is the essential cofactor for functional coupling (PubMed: 1513034).

Other names

Nitric oxide synthase 3NOS IIIConstitutive NOSEC 1.14.13.39

eNOS catalyzes the conversion of L-arginine and molecular oxygen into nitric oxide (NO) and L-citrulline. This reaction requires cofactors such as NADPH, FAD, FMN, and (6R)-5,6,7,8-tetrahydrobiopterin (BH4). Drugs like sapropterin act as exogenous BH4 to stabilize the eNOS dimer and prevent enzyme uncoupling, while statins and certain beta-blockers upregulate eNOS expression or activity to enhance NO bioavailability.