This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The following amino acid is essential for synthesis of nitric oxide: 
Select and explain. 
A. Arginine., B. Aspartate., C. Alanine., D. Glycine.
A: Arginine.
Answer: A: Arginine. 
Explanation: Harper – 572
Nitric oxide is formed by the action of the enzyme NO synthase, which is cytosolic.
The endothelial and neuronal forms of NO synthase are activated by Ca. The substrate is arginine, and the products are citrulline and NO.