This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acid Metabolism, Subject name: Biochemistry
Coenzyme for phenylalanine hydroxylase is - 
Select and explain. 
A. Tetrahydrofolate, B. Pyridoxal phosphate, C. S-adenosyl methionine, D. Tetrahydrobiopterin
D: Tetrahydrobiopterin
Answer: D: Tetrahydrobiopterin 
Explanation: Ans. is 'd' i.e., Tetrahydrobiopterino Phenylalanine metabolism is initiated by its oxidation to tyrosine which then undergoes oxidative degradation.