Nitric oxide synthase – NOS1, NOS2, NOS3

Nitric oxide synthase

Three important varieties of nitric oxide synthase involved in the synthesis of nitric oxide can be seen in the human system. They are neuronal, inducible and endothelial varieties.

nNOS: neuronal nitric oxide synthase (NOS1): Neuronal nitric oxide synthase is involved in the production of nitric oxide in both central and peripheral nervous system.

 iNOS: inducible nitric oxide synthase (NOS2): Inducible nitric oxide synthase also generates nitric oxide from L-arginine. Nitric oxide has an important role in blood pressure regulation and is also thought to have roles in infectious and malignant processes. iNOS is thought to be a mediator of non specific host defense in the clearance of bacterial, viral and fungal infections. Excess production of nitric oxide by iNOS is thought to have a role in the pathophysiology of vascular paralysis and hypotension in septic shock.

eNOS: endothelial nitric oxide synthase (NOS3): Endothelial nitric oxide synthase is the enzyme involved in the production of vascular nitric oxide. Nitric oxide is an important molecule which is vasoprotective and helps in the protection of atherosclerosis and thrombosis. Many of the coronary risk factors like cigarette smoking, hypertension, dyslipidemia and diabetes mellitus lead to the production of superoxides which react with nitric oxide, neutralizing its vasoprotective effect.

eNOS acts by oxidizing its substrate L-arginine to L-citrulline and nitric oxide. An essential cofactor tetrahydro-L-biopterin (BH4) is needed for this.