This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mechanisms of Enzyme Action, Subject name: Biochemistry
[{'content': 'Nitric oxide synthase: \nSelect and explain. \nA. Is inhibited by Ca++, B. Catalyze a de oxygenase reaction, C. Accept electron from NADH., D. Requires NADPH FAD, FMN, Heme iron.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. D. Requires NADPH FAD, FMN, Heme ironNitric oxide synthase is a very complex cytosolic enzyme which requires five redox co-factors: NADPH, FAD, FMN, Heme and tetrahydrobiopterin (FH4 ). NOS activity depends on increased conc, of Ca2++ ions.', 'role': 'assistant'}]