Conversion of phenylalanine to tyrosine is hampered in -

Ans. is 'a' i.e., Phenylketonuria o Phenylketonuria is characterized by inability of oxidation of phenylalanine into tyrosine.Phenylketonuriao It is an inborn metabolism of phenylalanine, in which there is inability of oxidation of phenylalanine into tyrosine. There is defective function ofphenylalanine hydroxylase, which may be due to : -i) Classical phenylketonuria (hyperphenylalanemia type I) -Deficiency of phenylalanine hydroxylase.ii) Atypical phenylketonuria (Hyperphenylalanemia type II and III) - Defect in dihydrobiopterin reductase.iii) Hyperphenylalanemia type - IV and V - Defect in dihydrobiopterin synthesis.o Phenylalanine level is raised as it can not be oxidized into tyrosine. Therefore, some minor pathways of phenylalanine metabolism become active (which does not require hydroxylase). This result in accumulation toxic metabolites of phenylalanine which include phenylpyruvate, phenylacetate, phenyllactat, and phenylacetylglutamine. Increased excretion of phenylalanine in urine gives the urine a mousy odor.o For detection of phenylalanine, following tests are used : -i) Guthrie's test: - It detect phenylalanine in the serum.ii) FeCl3: - It detects phenylalanine in urine. Phenylalanine gives green colour with FeCl3.iii) 2-4 Dinitrophenol hydrazine: - Gives yellow precipitate with old urine.o The main treatment is a phenylalanine restricted diet for life.