<prompt> Nitric oxide is synthesized from which amino acid:ArginineSerineThreonineLysine  <response>: NO is also called as Endothelium Derived Relaxing Factor EDRF. NO nitric oxide is synthesized from arginine by enzyme NOS Nitric oxide synthase in the endothelial cells. It requires 5 cofactors:- NADPH FAD FMN Heme and Tetrahydrobiopterin BH4. The vasodilator - nitroglycerin also enters smooth muscle cells, where its metabolism also leads to the formation of NO. NO synthase :-There are three isoforms of NOS Nitric oxide synthase 1. nNOS - neuronal 2. iNOS- inducible 3. eNOS- endothelial EC no. 1 oxido-reductase Mono oxygenase one oxygen is added in substrate Usually belongs to EC no 4 but NO synthase is an exception. 