Final answer:
Tyrosine becomes an essential amino acid for individuals with phenylketonuria (PKU) due to a deficiency in the phenylalanine hydroxylase enzyme, necessitating a diet low in phenylalanine and avoidance of aspartame.
Step-by-step explanation:
In persons with phenylketonuria (PKU), tyrosine becomes an essential amino acid due to a deficiency in the phenylalanine hydroxylase enzyme. This enzyme is responsible for converting phenylalanine into tyrosine. When this enzyme is deficient or defective, phenylalanine cannot be adequately processed and accumulates to toxic levels, causing damage to the central nervous system and brain. As a consequence, tyrosine must be obtained through the diet, making it a conditionally essential amino acid for individuals with PKU.
People with PKU must maintain a diet very low in phenylalanine to prevent brain damage and other severe symptoms. They must avoid foods and products, including aspartame, that are high in phenylalanine. Management of PKU often involves a carefully planned diet and may include treatment with the drug Kuvan for those with low phenylalanine hydroxylase activity levels.