<prompt> NO is synthesized fromTryptophanL - citrullineLysineL - arginine  <response>: NO nitric oxide:- Also called asEndothelium derived Relaxing Factor synthesized fromArginineby enzymeNOSNitric oxide synthase in the endothelial cells Nitric oxide relaxes the smooth muscles of blood vessels The vasodilator - nitroglycerin also enters smooth muscle cells, where its metabolism also leads to the formation of NO. Activates enzymeGuanyl cyclase, which conves GTP to cyclic GMP, which causes relaxation of smooth muscle cells 