This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET Jan 2020, Subject name: Biochemistry
No is synthesized from: 
Select and explain. 
A. L-arginine, B. L-citrulline, C. Glycine, D. Lysine
A: L-arginine
Answer: A: L-arginine 
Explanation: Also called asEndothelium derived Relaxing Factor NO (nitric oxide): - synthesized fromArginineby enzymeNOS(Nitric 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. There are three isoforms of NOS (Nitric oxide synthase) n NOS - neuronal i NOS- inducible e NOS- endothelial