Simplify the following text for a Grade 10 native English-speaking person.
Original: The enzyme phenylalanine hydroxylase normally converts the amino acid phenylalanine into the amino acid tyrosine .
Simplified: Normal people produce an enzyme called phenylalanine hydroxylase in their bodies . When they ingest phenylalanine , the body can not use it , so this enzyme changes phenylalanine into tyrosine , which the body can use .