Describe Biosynthesis of Non-Essential Amino Acids of Aromatic Amino Acid Family
The aromatic amino acid family primarily includes phenylalanine, tyrosine, and tryptophan. Among them, tyrosine is considered non-essential because it can be synthesized from phenylalanine in humans. Tryptophan and phenylalanine are essential and must be obtained from the diet.
1. Tyrosine Biosynthesis
Tyrosine is synthesized through the hydroxylation of phenylalanine in a reaction catalyzed by the enzyme phenylalanine hydroxylase.
Reaction:
Phenylalanine + O₂ + tetrahydrobiopterin (BH₄) → Tyrosine + H₂O + dihydrobiopterin (BH₂)
This reaction takes place in the liver and requires molecular oxygen and the cofactor BH₄. The enzyme phenylalanine hydroxylase is crucial, and any deficiency results in phenylketonuria (PKU), a metabolic disorder.
2. Role and Significance of Tyrosine
- Precursor for neurotransmitters like dopamine, norepinephrine, and epinephrine
- Precursor for melanin pigment and thyroid hormones
- Important for protein synthesis and cellular signaling
Pathway Context
Although tyrosine is synthesized from an essential amino acid, its classification as a non-essential amino acid reflects the body’s ability to synthesize it endogenously under normal physiological conditions.
The biosynthesis of tyrosine showcases the intricate interdependence between essential and non-essential amino acids in metabolic pathways and highlights the importance of maintaining balanced levels of dietary nutrients.