Nitric o, Xenopus/Amphibian,ide synthases (NOS) are enzymes that catalyze the generation of nitric o, Xenopus/Amphibian,ide (NO) from L-arginine and require nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor. At least three NOS isoforms have been identified: neuronal NOS (nNOS or NOS1 or bNOS), inducible NOS (iNOS or NOSII) and endothelial NOS (eNOS or NOS III). NOS-2 produces NO which is a messenger molecule with diverse functions throughout the body. In macrophages, NO mediates tumoricidal and bactericidal actions.