Nitric oxide synthase (NOS) is an enzyme responsible for producing nitric oxide (NO), a signaling molecule that plays a crucial role in various physiological processes. NOS converts the amino acid L-arginine into nitric oxide and L-citrulline, facilitating communication between cells and regulating functions such as blood flow, immune response, and neurotransmission. There are three main isoforms of NOS: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Each isoform is found in different tissues and has distinct regulatory mechanisms. The activity of NOS is essential for maintaining vascular health and modulating inflammation in the body.