Medical Genetics Phenylalanine I Phenylpyruvic acid Phenylketonuria Phenylalanine block hydroxylase Tyrosine 3, 4-dihydroxyphenylalanine (DOPA) Melanin pigments Tyrosine CO?+ H2o transaminase Citric acid cycle p-hydroxyphenylpyruvic acid Fumaric r Acetoacetic acid acid p-hydroxyphenylpyruvic Fumarylacetoacetic acid acid oxidase Homogentisic acid oxidase Homogentisic acid 2, 5-dihydroxyphenylacetic acid Maleylacetoacetic acid Phenylketonuria (Klug Cummings 1997)Medical Genetics