This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acid Metabolic Disorder, Subject name: Biochemistry
The enzyme deficient in Phenyl Ketonuria is: 
Select and explain. 
A. Phenylalanine dehydrogenase, B. Phenylalanine hydroxylase, C. Tyrosine hydroxylase, D. Dihydrobiopted n
B: Phenylalanine hydroxylase
Answer: B: Phenylalanine hydroxylase 
Explanation: Ref: Harpers illustrated Biochemistry, 28th editionExplanation: (See figure below)Tetrahydro biopterin (H4B) dependent reaction.In case of deficiency of phenyl alanine hydroxylase, phenyl alanine is converted in to phenylpyruvate & phenylacetate. accumulation of which results in phenyl ketonuria. FeaturesMental retardationLight color skin & hairEczema & seizures| Plasma phenylalanine| Phenylacetate & phenyl pyruvate in urineTreatment consists of limiting phenylalanine intake to levels barely adequate to support growth. Tyrosine, an essential nutrient for individuals with phenylketonuria, must be supplied in the diet.