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
[{'content': 'Which of the following is the ratelimiting enzyme in the biosynthesis of catecholamines? \nSelect and explain. \nA. Dopamine hydroxylase, B. Tyrosinase, C. DOPA decarboxylase, D. Tyrosine hydroxylase', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Tyrosine hydroxylase is the rate-limiting enzyme in the biosynthesis of catecholamines. Tyrosine is first hydroxylated to form 3,4- dihydroxyphenylalanine (DOPA) by the enzyme tyrosine hydroxylase. This enzyme is abundant in the central nervous system, the sympathetic ganglia, and the adrenal medulla Reference: Harpers illustrated biochemistry 30th edition', 'role': 'assistant'}]