This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
NO is synthesized by 
Select and explain. 
A. Uracil, B. Aspaate, C. Guanosine, D. Arginine
D: Arginine
Answer: D: Arginine 
Explanation: Nitric oxide is formed from Arginine by the enzyme Nitric oxide synthase.The enzyme utilizes NADPH and molecular oxygen. Citrulline is also formed.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 227