This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
The rate-limiting step in the biosynthesis of catecholamines is catalyzed by 
Select and explain. 
A. Tyrosine hydroxylase, B. Dopa decarboxylase, C. Dopa mine f3 hydroxylase, D. Catechol-O-methyltransferase
A: Tyrosine hydroxylase
Answer: A: Tyrosine hydroxylase 
Explanation: The rate limiting step in the synthesis of catecholamines is catalysed by tyrosine hydroxylase Ref : guyton and hall textbook of medical physiology 12 edition page number:605,606,607