ANS:A - phenylalanine to tyrosine

Disease conditions in amino acid metabolism is usually due to the lack of certain enzymes, phenylketonuria is due to the lack of phenylalanine hydroxylase, which is the enzyme involved in the conversion of phenylalanine to tyrosine. While ALkaptonuria is due to the lack of homogentisate dioxygenase in the conversion of Homogentisate to Maleylacetoacetate both of which are intermediates in the total conversion of phenylalanine to acetoacetyl coA.