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Metabolism of Phenylalanine and Tyrosine : Phenylketonuria (PKU), Alkaptonuria and Tyrosinemia

Phenylalanine and tyrosine are aromatic amino acids that play crucial roles in various biochemical pathways within the body. The metabolism of these amino acids is tightly regulated, and any disruptions can lead to metabolic disorders.

Phenylalanine Metabolism:
___________________________
Phenylalanine is an essential amino acid obtained from the diet and used for protein synthesis.
It is converted to tyrosine through the enzymatic action of phenylalanine hydroxylase (PAH), requiring the cofactor tetrahydrobiopterin (BH4).
A deficiency in PAH or BH4 leads to phenylketonuria (PKU), an inborn error of metabolism. PKU results in the accumulation of phenylalanine, leading to intellectual disabilities and other neurological problems if not managed through a restricted diet.

Tyrosine Metabolism:
______________________
Tyrosine is synthesized from phenylalanine and can also be obtained from the diet.
Tyrosine is a precursor for various important molecules, including catecholamines (e.g., dopamine, norepinephrine, epinephrine), thyroid hormones, and melanin.
Inborn Errors of Metabolism:

Phenylketonuria (PKU):
_______________________
As mentioned earlier, PKU is characterized by the inability to convert phenylalanine to tyrosine due to a deficiency in PAH or BH4.
If left untreated, elevated phenylalanine levels can lead to intellectual disabilities, developmental delays, and neurological problems. Early diagnosis and dietary intervention are critical for managing PKU.

Alkaptonuria:
______________
Alkaptonuria is a rare metabolic disorder caused by a deficiency in homogentisate 1,2-dioxygenase, an enzyme involved in the breakdown of tyrosine.
It leads to the accumulation of homogentisic acid, which can darken the urine and cause joint and connective tissue problems.

Tyrosinemia:
____________
Tyrosinemia is a group of rare genetic disorders characterized by the accumulation of tyrosine and its metabolites.
Tyrosinemia type I (HT1) is the most severe form and can lead to liver and kidney dysfunction if not treated early.

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