This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
"Classical phenyl ketonuria" is caused by deficiency of 
Select and explain. 
A. Phenylalanine transaminase, B. Phenylalanine hydroxylase, C. Tyrosine transaminase, D. Tyrosine hydroxylase
B: Phenylalanine hydroxylase
Answer: B: Phenylalanine hydroxylase 
Explanation: (Phenylalanine hydroxylase) (470 - RS 7th) (366 - U.S)PHENYLKETONURIA - 5 types of hyperphenylalaminemiasHYPER PHENYLALANINEMIASTypeConditionProbable enzyme defectTreatmentIClassical phenyl ketonuriaPhenylalanine hydroxylaseLow phenylalanine dietIIPeristent hyperphenyl alaninaemiaDecreased phenylalanine hydroxylase enzymeNone but temporary dietery therapyIIITransient mild hyperphenyl alaninaemiaMaturational delay of phenyl alanine hydroxylase enzymesSame as Type IIIVDihydropteridine reductase deficiencyDeficient or absent dihydropteridine reductaseDOPA, 5- 0 H tryptophan, carbidopaVAbnormal dihydrobiopterin functionDihydrobiopterin synthesis defectSame as type IV* Alkaptonuria - homogentisate oxidase deficiency enzyme* Type I Tyrosinaemia - Fumaryl acetoacetate hydrolase enzyme deficiency* Type II Tyrosinaemia - Hepatic transaminase enzyme deficiency* Hereditary tyrosinaemia - pOH - phenyl pyruvate oxidase enzyme deficiency