Phenylalanine hydroxylase is an enzyme found in the liver that plays a crucial role in the metabolism of the amino acid phenylalanine. It converts phenylalanine into another amino acid called tyrosine, which is important for producing neurotransmitters and hormones. This process is essential for maintaining proper levels of these compounds in the body. When there is a deficiency or malfunction of phenylalanine hydroxylase, it can lead to a genetic disorder known as phenylketonuria (PKU). Individuals with PKU cannot effectively break down phenylalanine, leading to its accumulation, which can cause serious health issues, including intellectual disabilities and developmental delays if not managed through diet.