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
Which of the following is the ratelimiting enzyme in the biosynthesis of catecholamines? 
Select and explain. 
A. Dopamine hydroxylase, B. Tyrosinase, C. DOPA decarboxylase, D. Tyrosine hydroxylase
D: Tyrosine hydroxylase
Answer: D: Tyrosine hydroxylase 
Explanation: 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