Nitric oxide (NO) is a versatile signaling molecule with diverse biological functions across a wide range of species. Its synthesis is catalyzed by nitric oxide synthases (NOS), which function as homodimers. Each NOS monomer contains two fused enzymatic domains: a cytochrome reductase and a cytochrome oxygenase. NOS activity requires three cosubstrates—L-arginine, NADPH, and oxygen—as well as five cofactors or prosthetic groups: FAD, FMN, calmodulin, tetrahydrobiopterin, and heme.
