Figure 1.

Schematic illustration of NOS dimer and NO formation from l-arginine. The two monomers are combined to form a dimer. The synthesis of NO depends on the presence of the substrate l-arginine and the cofactors including: molecular oxygen (O₂), nicotinamide adenine dinucleotide phosphate (NADPH), flavin adenosine dinucleotide (FAD), flavin mononucleotide (FMN), calmodulin (CaM) and tetrahydrobiopterin (BH4). In reaction, l-arginine with oxygen N^ω-hydroxy-l-arginine is first formed before l-citrulline and NO are produced (modified after [31]).