Phenylalanine hydroxylase

Definition

Phenylalanine hydroxylase is an enzyme responsible for converting the amino acid phenylalanine into tyrosine, a crucial step in the metabolic pathway of amino acid biosynthesis. This enzyme plays a vital role in the body's ability to synthesize neurotransmitters and hormones from amino acids, linking it directly to both the production of essential compounds and the regulation of nitrogen balance through the urea cycle.

5 Must Know Facts For Your Next Test

1. Phenylalanine hydroxylase requires tetrahydrobiopterin (BH4) as a cofactor for its enzymatic activity, which is crucial for the conversion process.
2. Deficiency in phenylalanine hydroxylase can lead to phenylketonuria (PKU), characterized by elevated levels of phenylalanine in the blood, which can cause severe developmental issues.
3. The enzyme's activity is influenced by various factors including pH, temperature, and substrate concentration, impacting how effectively it can convert phenylalanine to tyrosine.
4. Phenylalanine hydroxylase operates primarily in the liver, highlighting the organ's critical role in amino acid metabolism and regulation.
5. Regular screening for PKU at birth has been implemented in many countries to prevent serious health complications associated with high phenylalanine levels.

Review Questions

• What is the function of phenylalanine hydroxylase in amino acid metabolism, and what might happen if it is deficient?
  • Phenylalanine hydroxylase is essential for converting phenylalanine into tyrosine. If this enzyme is deficient, as seen in conditions like phenylketonuria (PKU), phenylalanine accumulates in the body. This buildup can lead to significant neurological impairments and developmental delays if not managed through dietary restrictions.
• How does the function of phenylalanine hydroxylase link to the urea cycle and overall nitrogen balance in the body?
  • Phenylalanine hydroxylase contributes to amino acid metabolism by facilitating the conversion of phenylalanine to tyrosine. This conversion helps manage nitrogen balance since both phenylalanine and tyrosine are part of broader metabolic pathways involving nitrogen. The urea cycle processes excess nitrogen from amino acid catabolism, helping prevent toxic buildup while utilizing resources efficiently.
• Evaluate the implications of untreated phenylketonuria (PKU) on an individual's health and development, considering the role of phenylalanine hydroxylase.
  • Untreated phenylketonuria (PKU) can have dire health consequences due to the inability of individuals to convert phenylalanine into tyrosine effectively. The accumulation of phenylalanine leads to neurotoxicity, resulting in cognitive deficits, behavioral problems, and developmental delays. Early detection through newborn screening and dietary management are critical interventions that mitigate these risks, emphasizing the importance of phenylalanine hydroxylase in preventing severe health outcomes.

Related terms

Tyrosine: An aromatic amino acid derived from phenylalanine that is a precursor for important neurotransmitters such as dopamine, norepinephrine, and epinephrine.

Phenylketonuria (PKU): A genetic disorder caused by a deficiency in phenylalanine hydroxylase, leading to the accumulation of phenylalanine in the body and potential neurological damage if untreated.

Urea Cycle: A series of biochemical reactions that convert ammonia, a toxic byproduct of amino acid metabolism, into urea for excretion from the body.