The NOS (Nitric Oxide Synthase) family consists of three isoforms: NOS1 (neuronal), NOS2 (inducible), and NOS3 (endothelial). They are composed of an oxidative-reductase domain and a domain for binding substrates and cofactors, distributed in various cells and tissues, such as neurons, immune cells, and vascular endothelial cells. NOS catalyzes the production of nitric oxide (NO) from L-arginine, participating in the regulation of vasodilation, neurotransmitter release, and immune response. By activating the cGMP signaling pathway, NO influences cellular function and physiological responses. The expression of NOS is tissue-specific, and mutations or dysregulation in its gene expression are associated with various diseases, including cardiovascular diseases, neurodegenerative diseases, and inflammatory responses.