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
Defect in phenylketonuria 
Select and explain. 
A. Phenylanine hydroxylase, B. Homogentisate oxidase, C. Pyruvate hydroxylase, D. Fumarylacetoacetate hydroxylase
A: Phenylanine hydroxylase
Answer: A: Phenylanine hydroxylase 
Explanation: In this condition phenylalanine can&;t be conveed to tyrosine, so phenylalanine accumulates and it&;s level in blood is elevated.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 236, fig 18.1