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: Unknown
[{'content': 'Nitric oxide is requires which of the following AA \nSelect and explain. \nA. Arginine, B. Serine, C. Threonine, D. Lysine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref. Guyton. 13th edition. Page. 208\nSynthesis of NO\nNitric oxide is produced by a group of enzymes called nitric oxide synthases.\nThese enzymes convert arginine into citrulline, producing NO in the process.\n\nOxygen and NADPH are necessary co-factors.\nThere are three isoforms of nitric oxide synthase (NOS)\nThe isoforms of NOS are neuronal NOS (or nNOS), endothelial NOS (or eNOS) and inducible NOS (or iNOS).', 'role': 'assistant'}]